Method for producing an EUV mirror component, intermediate product of an EUV mirror component

Abstract

A method for producing an EUV mirror component (M1-M6, 40), in which a multilayer coating system (31) is applied to a surface of a mirror body substrate (30, 37) in order to form an optical surface that is highly reflective for EUV radiation. A temporary protective coating structure (36) is produced on the multilayer coating system (31). The protective coating structure (36) comprises a protective layer (35) and a sacrificial layer (34) arranged between the protective layer (35) and the multilayer coating system (31). The temporary protective coating structure (36) is removed before the EUV mirror component is put into operation. The invention also relates to an intermediate product of an EUV mirror component.

Description

The invention relates to a method for producing an EUV mirror component. The invention also relates to an intermediate product of an EUV mirror component.Microlithographically projected exposure apparatuses are used for the production of integrated circuits having particularly small structures. A photomask illuminated with very short-wave, extreme ultraviolet radiation (EUV radiation) is imaged onto a lithography object in order to transfer the mask structure to the lithography object.The projection exposure apparatus comprises a plurality of EUV mirrors which have an optical surface at which the EUV radiation is reflected. In order to keep the losses of EUV radiation within the projection exposure apparatus low, the EUV mirrors have an optical surface with high reflectivity for EUV radiation. The optical surface is formed by a multilayer system from which incident EUV radiation is reflected back.In addition to the projection exposure apparatus itself, there are further optical systems which are operated in conjunction with microlithographically projecting exposure apparatuses. These include, for example, measuring devices with which the reflectivity of EUV mirrors is examined, devices for examining modules and subsystems, and measuring devices with which the properties or the state of photomasks are examined. EUV mirrors are also used in such optical systems.Between the application of the multilayer system to a mirror body substrate and the subsequent startup of the relevant EUV mirror component, there is an intermediate phase in which the EUV mirror component can be exposed to various influences. For example, the EUV mirror component can be stored, packaged, transported or mounted. It is also possible for further processing steps to be carried out on the EUV mirror component.It has been found that in this intermediate phase, contaminants or damage can occur to the multilayer system. Possible adverse effects include mechanical damage caused by cutting processes (e.g. laser cutting), (chemical) layer damage caused by etching media, photoresists and / or solvents, contamination caused by environmental influences and / or inadequate removal of an applied layer (e.g. photoresist), particle contamination caused by inadequate removal of an applied layer (e.g. photoresist), change in the surface termination caused by chemical interactions of the surface within a structuring process, layer roughening caused by etching media, photoresists and / or solvents, diffusion of solvents and / or etching media caused by the EUV layer and resulting layer detachment during the later use of the EUV mirror component, and light- or particle-based radiation damage. All these influences can lead to an impairment of the multilayer system and thus to a reduced quality of the optical surface of the EUV mirror component.The object of the invention is to provide a method for producing an EUV mirror component and an intermediate product of an EUV mirror component, with which these disadvantages are avoided. The object is achieved with the features of the independent claims. Advantageous embodiments are specified in the dependent claims.In the method according to the invention for producing an EUV mirror component, a multilayer layer system is applied to a surface of a mirror body substrate in order to form an optical surface which is highly reflective for EUV radiation. A temporary protective layer structure is produced on the multilayer system. The protective layer structure comprises a protective layer and a sacrificial layer arranged between the protective layer and the multilayer system. The temporary protective layer structure is removed before the EUV mirror component is put into operation.The invention is based on the finding that, due to conflicting requirements, it is not quite simple to protect the optical surface from adverse effects in the intermediate phase. Although protective layers are fundamentally known which can be applied to the multilayer system and which offer adequate protection against environmental influences occurring. However, it has proved difficult to remove such protective layers from the multilayer system again without damaging the multilayer system. In contrast, layers which can be removed easily and without impairing the multilayer system usually do not provide sufficient protection against the loads occurring.The invention proposes a temporary protective layer structure which comprises a protective layer and a sacrificial layer arranged between the protective layer and the multilayer system. The protective layer can be composed in such a way that it offers sufficient protection against the loads occurring. The fact that process steps of higher aggressiveness are required for removing such a protective layer can be accepted because the aggressive process steps can be prevented from acting as far as into the multilayer system by the sacrificial layer below. Subsequent to the removal of the protective layer, the sacrificial layer may be removed using less aggressive processing steps. The less aggressive process steps can be selected such that the multilayer system is not impaired.The temporary protective layer structure can ensure that damage to the multilayer system does not occur in the intermediate phase between the application of the multilayer system to the mirror body substrate and the startup of the EUV mirror component. After the temporary protective layer structure has been removed, the EUV mirror component can be put into operation with a perfect optical surface.The multilayer system may comprise alternating layers of molybdenum and silicon. With such a coating, approximately 70% of the incident EUV radiation can be reflected. The multilayer system can be optimized for the reflection of EUV radiation in the extreme ultraviolet spectral range with wavelengths between 5 nm and 30 nm, in particular with a wavelength of 13.5 nm.The multilayer system can comprise a terminating layer which consists of a different material than underlying alternating layers of the multilayer structure. After removal of the temporary layer structure, the terminating layer can form the surface of the EUV mirror component. The terminating layer can assume a protective function during the later operation of the EUV mirror component in order to counteract rapid degradation of the multilayer system, for example. The termination layer may be made of an inorganic material. The termination layer may consist of ruthenium, TiO 2 or rhenium, for example. The terminating layer may have a thickness between 1 nm and 20 nm, preferably a thickness between 2 nm and 10 nm.The sacrificial layer may be a layer applied to the multilayer system. The sacrificial layer can be applied directly to the terminating layer of the multilayer system. The material for the sacrificial layer may be selected to meet one or more of the following requirements. The sacrificial layer should be removable without leaving any residue without the multilayer system being damaged or contaminated, which can be achieved in particular by a high purity of the material of the sacrificial layer. The sacrificial layer should have good adhesion to the surface of the multilayer system. The sacrificial layer should form a good adhesion base for the protective layer. The sacrificial layer should have high wetting on the surface of the multilayer system. The surface of the sacrificial layer should have a lower roughness in order to avoid adverse effects on subsequent processing steps.In one embodiment, the sacrificial layer is a carbon layer. The carbon layer preferably consists to an extent of at least 80%, more preferably to an extent of at least 90%, more preferably to an extent of at least 99.99%, of carbon. Percentages of the amounts of materials in a layer are based on the number of particles present in the layer. The surface energy of carbon is lower than that of metals. Good coverage of the multilayer system is therefore to be expected. Carbon has the advantage that it can be removed by using a hydrogen plasma. When using a hydrogen plasma, there is no risk of damage to the multilayer system, because the optical surface is exposed to a hydrogen plasma anyway during EUV operation. Other methods of removing the carbon layer are possible. The carbon layer can have a thickness of between 1 nm and 30 nm, preferably between 2 nm and 5 nm, for example.Examples of alternative materials for the construction of the sacrificial layer are: nitrides; smoothly growing, high-purity carbon compounds with a high sublimation point, such as, for example, higher acens; carbon compounds with a low sublimation point, which can be removed by heating to a temperature of less than 350° C.; metals; 2D materials, such as, for example, graphene or transition metal dichalcogenides. In the case of an organic material for the sacrificial layer, the layer thickness is preferably less than 30 nm. In the case of an inorganic sacrificial layer, the layer thickness can be, for example, between 10 nm and 300 nm.Possible methods for applying the sacrificial layer are sputtering, electron beam deposition, chemical vapor deposition, physical vapor deposition, atomic layer deposition, spin coating (spin coating), spray coating. Combinations of these methods are also possible. In general, the application of the sacrificial layer should be carried out in such a way that the multilayer system is not damaged by the application of the sacrificial layer. In particular, a temperature of 350° C. should not be exceeded.Instead of applying the sacrificial layer to the multilayer system, the sacrificial layer can also be produced by converting the terminating layer of the multilayer system. In one embodiment, the sacrificial layer is formed by oxidation of the termination layer. If the sacrificial layer is produced by oxidation, this has the advantage that the step of an additional layer application for the sacrificial layer can be omitted. A further advantage can result from the fact that an oxide of the terminating layer of the multilayer system generally has only slight effects on the reflectivity of the optical surface for EUV radiation. It can therefore be accepted if the sacrificial layer is not completely removed before the EUV mirror component is put into operation, but if residues of the oxide remain. In this case too, however, the sacrificial layer should be removed at least to a very predominant extent, in particular to an extent of at least 80%, preferably to an extent of at least 90%, more preferably to an extent of at least 95%.It is also possible to produce a sacrificial layer having a first sub-layer and a second sub-layer. The first sublayer adjoining the multilayer system can be optimized for easy removability. The second sub-layer of the sacrificial layer may be optimized to form a suitable basis for the application of the protective layer. For example, the second sub-layer of the sacrificial layer can form a surface which can be wetted well by the material of the protective layer. It is also possible for the second sublayer to form a separating layer between the protective layer and the first sublayer of the sacrificial layer, for example if the material of the protective layer would be aggressive for the first sublayer of the sacrificial layer. Additionally or alternatively, the second sub-layer of the sacrificial layer may be selected to have sufficient resistance to the deposition process with which the protective layer is applied and / or to the cleaning process with which the protective layer is removed.After the sacrificial layer is formed, the protective layer may be applied to the sacrificial layer. The material of the protective layer should be selected to meet one or more of the requirements mentioned below. Stability with respect to mechanical stress, stability with respect to etching media, stability with respect to photoresists and / or solvents, stability with respect to temperatures up to 350° C., effective diffusion barrier for oxygen and / or photoresist and / or solvent, good adhesion to the sacrificial layer, low roughness in order not to adversely affect further processing steps, residue-free removability without damage or contamination of the EUV layer. The thickness of the protective layer may be between 0.1 μm and 10 μm, for example.In one embodiment, the protective layer is applied as a protective varnish, which has corresponding properties. In particular, the protective layer can be formed by a protective lacquer in the form of a photoresist. In one embodiment, the protective varnish has a good layer relationship, such that the protective layer can be removed from the sacrificial layer in a manner similar to a film. In the case of a protective layer in the form of a protective lacquer, the layer thickness can be, for example, between 1 μm and 10 μm.In an alternative embodiment, the protective layer is formed by applying silicon dioxide SiO 2 thereon. Silicon dioxide has sufficient resistance to perform the desired protection function. For example, an HF vapor process having high selectivity for the removal of silicon dioxide can be used to remove a layer of silicon dioxide. In the case of a protective layer made of silicon dioxide, the layer thickness can be, for example, between 0.1 μm and 0.3 μm. It is also possible to form the protective layer from other suitable oxides, in particular from other suitable silicon oxides.The protective layer and the sacrificial layer can be removed from the surface of the multilayer system in two separate processes. It is also possible to remove the protective layer and the sacrificial layer from the surface of the multilayer system in a uniform process. Generally, the protective layer and the sacrificial layer should be removed to meet one or more of the requirements set forth below. Damage to the multilayer system should be avoided. The protective layer and the sacrificial layer should be removed without residue, so that no contamination remains on the surface of the multilayer system. An increased particle load or roughening of the surface of the multilayer system should be avoided. A surface temperature of 350°C should not be exceeded using suitable non-thermal methods or by using suitable cooling of the substrate.Methods which are generally suitable for removing the protective layer and / or the sacrificial layer are: dry chemical methods, such as, for example, the use of HF vapor, CF4, CHF3, etc.; plasma cleaning, for example by means of H plasma and / or O plasma; cleaning with an ion beam source; wet chemical cleaning; laser cleaning; the use of CO 2- beams; annealing at temperatures below 350° C. and / or suitable substrate cooling; peeling off the protective layer as a film. It is possible, when removing the protective layer and / or the sacrificial layer, to combine these cleaning methods with one another and / or to use them one after the other.If the protective layer is formed by a protective lacquer, it can be advantageous to use a wet chemical method for removing the protective layer. In a wet chemical process, the protective layer is treated with a liquid solvent to dissolve the structure of the protective layer. Wet chemical methods generally have the advantage that particles and contaminants are reliably removed both on the protective layer and in the interior of the protective layer. The solvent may be selected so as not to attack the sacrificial layer beneath.The use of a dry chemical method for removing the protective layer can be advantageous if the protective layer consists of silicon dioxide. In particular, the protective layer can be removed by using an HF vapor process having high selectivity for removing silicon dioxide. If the protective layer is completely dissolved in this way, particles and contaminants can be removed both on the protective layer and within the protective layer.If a contamination layer has formed on the protective layer structure or within the protective layer structure, for example by deposition of particles or by oxidation, this contamination layer can be removed before the respective underlying layer is removed. One possible method for removing the contamination layer is the use of an oxygen plasma.The removal of the protective layer can be followed by the removal of the sacrificial layer. A gentle method is suitable for this purpose in order to avoid damage to the multilayer system. A generally suitable method is, for example, the use of a hydrogen plasma (H* plasma or H' plasma). This applies in particular if the sacrificial layer is a carbon layer. In the case of a sacrificial layer produced by oxidation of the terminating layer of the multilayer system, too, the removal can be effected by means of hydrogen plasma. This can be combined with a physical etching process, such as the prior application of a noble gas plasma, if necessary. The noble gas plasma may be, for example, a neon plasma, an argon plasma or a krypton plasma.The application of the multilayer system to the mirror body substrate can be effected in a process chamber under vacuum conditions. The production of the sacrificial layer of the temporary protective layer structure according to the invention can follow this without the EUV mirror component leaving the process chamber. If the vacuum is maintained between the application of the multilayer system and the production of the sacrificial layer, the risk of contamination is reduced.The vacuum can also be maintained until the protective layer of the temporary protective layer structure is also applied. In one embodiment, the protective layer is produced in the same process chamber as the multilayer film system.The method can be carried out such that the EUV mirror component is not subjected to any further processing steps in the intermediate phase between the production of the temporary protective layer structure and the removal of the temporary protective layer structure. The function of the protective layer structure can consist primarily in protecting the optical surface during transport and storage.In another embodiment, one or more processing steps are carried out on the EUV mirror component in the intermediate phase. In particular, the EUV mirror component can be subjected to a processing step with which material is ablated from the multilayer structure and / or from the substrate of the EUV mirror component. For example, a processing step can be carried out with which a structuring is generated in the optical surface of the EUV mirror component. The structuring can be produced by a lithography method. For this purpose, a photoresist applied to the optical surface of the EUV mirror component can be locally exposed in accordance with the structuring to be generated. The processing steps can be carried out in the regions of the optical surface in which the photoresist has been locally removed.Additionally or alternatively, one or more of the processing steps mentioned below may be carried out. Mechanical processing can be carried out, for example for delimiting the optical surface and / or for processing the substrate contour. A thermal treatment may be performed, for example, to change the state of a layer or the substrate or for the purpose of soldering or gluing. In one embodiment, annealing is performed without vacuum. A chemical treatment, for example for the purpose of structuring, which can be carried out wet-chemically, from the gas phase or by ion beam etching, is also possible. In one embodiment, the chemical treatment is in combination with a lithographic process. A further variant is irradiation with ions, with electrons, with UV radiation or with X-ray radiation.The function of the protective layer structure according to the invention can be to provide protection to the optical surface during the execution of the processing steps.In the case of structuring using a photoresist, the photoresist can simultaneously be the protective layer of the temporary protective layer structure. In another embodiment, the photoresist is applied to the protective layer of the temporary protective layer assembly. The photoresist can then be removed in a common process step with the protective layer. It is also possible to remove the photoresist separately from the protective layer in a preceding method step.The structuring can serve to subdivide an area continuously covered with a multilayer layer system into a multiplicity of mirror elements. With the processing steps, parts of the mirror body substrate can be removed in order to create flexure joints within the mirror body substrate, so that each of the mirror elements is hingedly connected to a main body of the mirror body substrate via a flexure joint. The mirror body substrate can consist of silicon, in particular of monocrystalline silicon. The temporary protective layer structure according to the invention can have the function of protecting the optical surface--insofar as it is retained--during these processing steps. An EUV mirror component comprising a multiplicity of individual mirror elements can be used, for example, as a facet mirror, in particular as a MEMS facet mirror in the illumination system of a microlithographically projected exposure apparatus.It is also possible to use a sequence of method steps in which the processing steps are carried out first, with which the optical surface is divided into a plurality of mirror elements, and the temporary protective layer structure is then produced. This opens up the possibility that the temporary protective layer structure protects outer surfaces of the mirror elements which lie between the optical surface and the flexure bearings.In one embodiment, the temporary protective layer structure is produced on an optical surface which is not subjected to any further structuring, such that the EUV mirror component has a uniform and continuous optical surface during the later use. Such EUV mirrors can be used in an optical system, such as a projection objective of a microlithography projection exposure apparatus, in order to deflect and shape an EUV beam path. These mirrors frequently have high requirements for the geometric shape of the optical surface. In order to be able to meet these, the mirror body can be made of a material whose coefficient of thermal expansion has a zero crossing (zero crossing temperature). An example of such a material is a titanium silicate glass known as ULE™ (Ultra Low Expansion), or ZERO-DUR™ glass. In such an embodiment, the temporary protective layer structure may have the function primarily of protecting the optical surface during transport and storage and also in steps other than structuring the optical surface. These include, for example, adhesive steps in which the optical surface is protected from adhesive vapors by the temporary protective layer structure.Generally, materials for the substrate of the mirror body also include metallic materials, monocrystalline materials or glass. In one embodiment, the mirror substrate material is silicon, in particular single crystal silicon.The removal of the temporary protective layer structure may be performed in a separate operation before the EUV mirror component is mounted in an optical system. In this procedure, there is a risk that damage or impurities can occur on the optical surface of the EUV mirror component in the phase between the removal of the temporary protective layer structure and the mounting. In one embodiment, therefore, the sacrificial layer is not removed until the mounting of the EUV mirror component into the optical system has taken place. This is particularly appropriate if the sacrificial layer is removed by using a hydrogen plasma to which the multilayer system can be exposed anyway during later operation. The removal of the protective layer may have taken place in a preceding step before the mounting of the EUV mirror component. The possibility that both the sacrificial layer and the protective layer are removed after the mounting of the EUV mirror component is likewise included.The invention also relates to an intermediate product of an EUV mirror component. A multilayer layer system is applied to one surface of the mirror body substrate, said multilayer system forming an optical surface which is highly reflective for EUV radiation. A temporary protective layer structure is arranged on the multilayer system. The protective layer structure comprises a protective layer and a sacrificial layer arranged between the protective layer and the multilayer system.The disclosure comprises developments of the method with features which are described in connection with the EUV mirror component intermediate product according to the invention. The disclosure comprises developments of the EUV mirror component intermediate product with features which are described in connection with the method according to the invention.The invention is described below by way of example with reference to the attached drawings on the basis of advantageous embodiments. The following are shown: FIG. 1 : a microlithographically projected exposure apparatus; FIG. 2 : a section of an EUV mirror component; FIG. 3 : the view according to FIG. 2 in a second state of the EUV mirror component; FIG. 4 : the view according to FIG. 2 in a third state of the EUV mirror component; FIG. 5 : the view according to FIG. 2 in a fourth state of the EUV mirror component; FIGS. 6 to 8 : different intermediate states during the production of a facet mirror; FIG. 9 is a view according to FIG. 7 in an alternative embodiment of the invention; FIG. 10 : shows an illustration of a method sequence according to the invention; FIG. 11 is a view according to FIG. 10 in an alternative embodiment of the invention.FIG. 1 schematically illustrates a microlithographically EUV projection exposure apparatus. The projection exposure apparatus comprises an exposure beam source 14, an illumination system 10 and a projection objective 22, which are operated together in a vacuum chamber 23.The exposure beam source 14 generates electromagnetic radiation in the EUV range, i.e. in particular with a wavelength between 5 nm and 30 nm. The exposure radiation emanating from the exposure beam source 14 is focused by a collector 15 into an intermediate focal plane 16. Exposure radiation passing out of the intermediate focus plane 16 is guided by the illumination system 10 into an object plane 12, so that an object field in the object plane 12 is illuminated with uniform radiation intensity.The illumination system 10 comprises a deflection mirror 17 with which the exposure radiation is deflected onto a first facet mirror 18. A second facet mirror 19 is arranged downstream of the first facet mirror 18. The facets of the first facet mirror 18 are imaged into the object plane 12 by the second facet mirror 19.A photomask 13 is arranged in the object plane 12, which is imaged into an image plane 21 via a plurality of mirrors M 1-M 6 of the projection objective 22. A pattern formed on the photomask 13 is transferred to a radiation sensitive layer of a wafer 20 disposed in the image plane 21. The photomask 13 hangs on a first scanning device 24, the wafer 20 rests on a second scanning device 25, so that the wafer 20 can be exposed in a scanning process in which the photomask 13 and the wafer 20 are moved synchronously with one another.Each of the EUV mirrors 17, 18, 19, M 1-M 6 in FIG. 1 is provided with a multilayer system which forms an optical surface with high reflectivity for EUV radiation. This is explained in more detail below with reference to FIG. 2 using the example of the mirror M 1. Shown in FIG. 2 is an enlarged sectional illustration of a section of the mirror M 1.Mirror M1 includes a mirror body 30 made of ultra-low thermal expansion ("ultra-low expansion") mirror substrate material. Examples of such materials are a titanium silicate glass or ZERODUR™ sold under the name ULE™ which both have a so-called zero crossing temperature (="zero crossing temperature"). At this zero crossing temperature, which for example for ULE™ is approximately 30° C., the thermal expansion coefficient has a zero crossing in its temperature dependence, in the vicinity of which there is no or only negligible thermal expansion of the mirror substrate material.A multilayer system 31 with alternating layers 32 of molybdenum and silicon is applied to the mirror body 30. The layers 32 of the multilayer system 31 can each have a thickness of the order of magnitude of, for example, 5 nm. The multilayer system 31 comprises a termination layer 33, which has good resistance to influences occurring during operation of an EUV mirror. The terminating layer 33 can have a somewhat greater thickness than the remaining layers 32 of the multilayer system and can be between 1 nm and 20 nm thick, for example. The termination layer 33 can consist, for example, of ruthenium, TiO 2 or rhenium.In FIG. 2, the EUV mirror M 1 is shown in the state in which it is used in the microlithographically projected exposure apparatus. The terminating layer 33 of the multilayer system 31 forms the surface of the EUV mirror M 1 during operation of the projection exposure apparatus.The state according to FIG. 2 is also reached during production by the EUV mirror M 1 at a point in time immediately after the multilayer layer system 31 has been applied to the mirror body 30. Between this point in time and the startup of the EUV mirror M 1 in the projection exposure apparatus, there is an intermediate phase which can extend over a longer period of time. In the intermediate phase, the EUV mirror M 1 is subjected to various handling steps, such as storage, packaging, transport, unpacking and the like. In the state shown in FIG. 2, the surface of the multilayer system 31 would be exposed to a direct effect of environmental influences, which would entail a risk of contamination or damage to the multilayer system 31.The invention proposes protecting the multilayer system 31 during the intermediate phase with a protective layer structure 36, see FIGS. 3, 4. The sacrificial layer 34 is optimized in that it forms a good basis for the application of the protective layer 35 and in that it can be removed again easily and in particular without leaving any residue before the EUV mirror M 1 is put into operation, without the terminating layer 33 of the multilayer system 31 being damaged. The protective layer 35 is optimized for a good protective effect in order to ensure that influences occurring in the intermediate phase cannot cause damage to the multilayer system 31. If more aggressive steps are required to remove the protective layer 34 again before the EUV mirror M 1 is put into operation, this can be accepted because the aggressive steps are prevented from acting as far as into the multilayer system 31 by the sacrificial layer 34 lying underneath.FIG. 3 shows the EUV mirror M 1 in a state in which the sacrificial layer 34 is applied to the terminating layer 33 of the multilayer system 31. The sacrificial layer 34 is applied in the same process chamber in which the terminating layer 33 of the multilayer system 31 has also been applied beforehand. Both the application of the finishing layer 33 and the application of the sacrificial layer 34 are carried out under vacuum, wherein the vacuum is maintained continuously during the two steps and between the two steps. The sacrificial layer 34 has a surface that provides a good basis for the subsequent protective layer 35.The application of the protective layer 35 can be carried out in a separate process chamber. A state of the EUV mirror M 1 in which the complete protective layer structure 36 with the sacrificial layer 34 and the protective layer 35 is applied is shown in FIG. 4.Before the EUV mirror M 1 is put into operation, the protective layer structure 36 is removed again. FIG. 5 shows an intermediate state in which the protective layer 35 has been removed and the sacrificial layer 34 is still present in a state which it has after the action of the aggressive process steps with which the protective layer 35 has been removed. In particular, the sacrificial layer may have an uneven and / or damaged surface that is unsuitable for applying further layers.After the remaining sacrificial layer 34 has also been removed with a gentler method, the EUV mirror M 1 again has the state shown in FIG. 2. The EUV mirror M 1 is ready to be put into operation in the microlithographically projected exposure apparatus.FIGS. 6 to 8 show different stages in the production of a component for the first facet mirror 18 or the second facet mirror 19 of the microlithographically projected exposure apparatus from FIG. 1. A substrate body 37 is provided which consists of monocrystalline, polycrystalline or amorphous silicon. A multilayer system 31 corresponding to FIG. 2 is applied to a surface of the substrate body 37.A protective layer structure 36 is applied to the multilayer system 31, the protective layer 35 of which is formed by a photoresist. By suitable exposure of the photoresist, regions are defined in which material is removed by a subsequent processing step. FIG. 7 shows a state in which material is ablated between individual EUV mirror components 40, such that the EUV mirror components 40 are separated from one another as far as into the substrate body 37. Each EUV mirror component 40 has a mirror body 30, which is connected to the remaining base of the substrate body 37 via a diagrammatically illustrated solid state joint 39. The protective layer structure 36 ensures that the multilayer system 31 does not damage in the regions in which it is intended to form the optical surface of the EUV mirror components 40.Each of the facet mirrors 18, 19 is composed of a plurality of components of the type shown in FIG. 7. Before the startup of a facet mirror 18, 19 in the microlithographically projecting exposure apparatus, the protective layer structure 36 is removed, with the result that the EUV mirror components 40 obtain their final state shown in FIG. 8.FIG. 9 shows an alternative exemplary embodiment in which the multilayer system 31 is applied only after suitable structuring of the substrate body 37. A protective layer structure 36 is applied to the multilayer system 31, protecting the optical surface and the side surfaces of the EUV mirror components 40.With reference to FIG. 10, an embodiment of a protective layer structure 36 according to the invention is explained. A schematic time ray T shows the sequence in which layers on the surface of the mirror body add and are removed again. In a first step, a carbon layer having a thickness between 2 nm and 5 nm is applied to the terminating layer 33 of the multilayer system 31 by vapor deposition. The carbon layer forms a sacrificial layer 34 in the sense of the invention.The subsequent step with which the protective layer 35 is applied takes place in another process chamber. During transport thereto, the EUV mirror is exposed to an oxygen-containing atmosphere in the exemplary embodiment shown, which has the result that the sacrificial layer 34 can oxidize and that impurities are deposited. In FIG. 10, a corresponding contamination layer 41 is shown on the sacrificial layer 34. There are other embodiments without such a contamination layer.The protective layer 35 is applied to the contamination layer 41. In this embodiment, the protective layer 35 is formed by a resist applied by spin coating (spin coating). The protective varnish has a thickness of between 1 μm and 10 μm.A photoresist 42 is applied again to the protective layer 35 by way of spin coating. The photoresist 42 may be selectively exposed to define regions for subsequent patterning.Before the EUV mirror is put into operation in the projection exposure apparatus, the layers are removed again one after the other until the terminating layer of the multilayer layer system 31 is exposed. First, solvents are used to remove the photoresist 42 and the resist 35 by wet chemical methods. The sacrificial layer 34 made of carbon is not attacked by the solvents. The contamination layer 41 is removed by exposing the surface of the EUV mirror to an oxygen plasma if the sacrificial layer is insensitive thereto. The removal of the sacrificial layer 34 takes place only after the installation of the EUV mirror in the projection exposure apparatus by the surface of the EUV mirror being exposed to a hydrogen plasma. The projection exposure apparatus with the EUV mirror is then ready for use.The carbon as material of the sacrificial layer 34 has a lower surface energy than metals, so that good coverage of the multilayer system 31 by the terminating layer 33 can be expected. The residue-free removability of the sacrificial layer 34 from the end layer 33 is thus promoted. The wet chemical processes for removing the photoresist 42 and the protective layer 35 facilitate the removal of particles and contaminants on and in the layers. By using only chemical processes and not physical etching processes for removing the layers, material removal is very selective.In the exemplary embodiment according to FIG. 11, the sacrificial layer 34 is produced by oxidation of the terminating layer 33 of the multilayer system 31. An oxide layer having a thickness of a few nanometers is formed. A protective layer 35 of silicon dioxide is applied to the oxide layer 34 by means of the vapor deposition, which protective layer is between 100 nm and 300 nm thick. During a subsequent storage of the EUV mirror, a contamination layer 41 can form on the protective layer 35. The resist 42 for structuring the surface is applied to the contamination layer 41 by spin coating. The thickness of the photoresist layer is again between 1 μm and 10 μm.Before the EUV mirror is put into operation in the projection exposure apparatus, the layers are removed. The removal of the photoresist 42 is again carried out by using solvents. The contamination layer 41 is removed by application of an oxygen plasma. The protective layer of silicon dioxide can be removed by using HF vapor. For example, a hydrogen plasma may be used to remove the oxide layer forming the sacrificial layer 34. Alternatively, the removal of the sacrificial layer may be performed by physical sputtering (e.g., noble gas plasma) or by applying RF vapor.This exemplary embodiment has the advantage that no separate deposition of the sacrificial layer 34 is required. By removing the protective layer structure 36 by dry chemical methods, the multilayer system 31 is saved. By completely dissolving the protective layer 35 by applying HF vapor, contaminants and particles on and in the layer can be reliably removed. By using complementary deposition and ablation techniques, separation of functionalities is facilitated. If the sacrificial layer 34 is removed only incompletely, this can be accepted because small residues of the oxide of the termination layer 33 do not substantially impair the reflectivity of the multilayer layer system 31 for EUV radiation.

Claims

Method for producing an EUV mirror component (M1-M6, 40), in which a multilayer film system (31) is applied to a surface of a mirror body substrate (30, 37) in order to form an optical surface which is highly reflective for EUV radiation, wherein a temporary protective layer structure (36) is produced on the multilayer film system (31), wherein the protective layer structure (36) comprises a protective layer (35) and a sacrificial layer (34) arranged between the protective layer (35) and the multilayer film system (31), and wherein the temporary protective layer structure (36) is removed before the EUV mirror component is put into operation.Method according to claim 1, wherein the multilayer system (31) comprises a terminating layer (33) which consists of a different material than underlying alternating layers (32) of the multilayer structure (31).Method according to claim 1 or 2, wherein the sacrificial layer (34) is a layer which is applied to the multilayer system (31).The method of claim 3, wherein the sacrificial layer (34) is a carbon layer.The method according to claim 4, wherein the carbon layer has a thickness between 1 nm and 30 nm, preferably between 2 nm and 5 nm.Method according to claim 1 or 2, wherein the sacrificial layer (34) is a layer which is produced by oxidation of a layer of the multilayer system of layers (31).Method according to one of Claims 1 to 6, wherein the protective layer (35) is applied as a protective lacquer.The method of claim 7, wherein the resist is a photoresist.The method according to any one of claims 1 to 6, wherein the protective layer (35) is formed by silicon dioxide.Method according to one of Claims 1 to 9, wherein a temperature of 350°C is not exceeded when the protective layer structure (36) is removed.Method according to one of Claims 1 to 10, wherein the EUV mirror component (M1-M6, 40), after the production and before the removal of the temporary protective layer structure (36), is subjected to a processing step with which material is ablated from the multilayer structure (31) and / or from the mirror body substrate (37).Method according to Claim 11, wherein an area continuously covered with a multilayer system (31) is divided into a plurality of mirror elements (40).EUV mirror component intermediate product having a multilayer layer system (31) which is applied to a surface of a mirror body substrate (30, 37) and forms an optical surface which is highly reflective for EUV radiation, wherein a temporary protective layer structure (36) is arranged on the multilayer layer system (31), wherein the protective layer structure (36) comprises a protective layer (35) and a sacrificial layer (34) arranged between the protective layer (35) and the multilayer layer system (31).

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