Method for manufacturing an EUV mirror component, and intermediate product of an EUV mirror component

Abstract

The invention relates to a method for manufacturing an EUV mirror component (M1-M6, 40), in which method 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 layer structure (36) is created on the multilayer coating system (31). The protective layer structure (36) comprises a protective layer (35) and a sacrificial layer (34) located between the protective layer (35) and the multilayer coating system (31). The sacrificial layer (34) is a layer produced by oxidising a layer of the multilayer coating system (31). The temporary protective layer 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

[0001] Method for producing an EUV mirror component, intermediate product of an EUV mirror component

[0002] This patent application claims priority from German patent application DE 10 2023 212 037 . 2, filed on November 30, 2023, to which reference is made and the contents of which are incorporated herein in their entirety ( "incorporation by reference").

[0003] 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.

[0004] Microlithographic projection exposure systems are used for the production of integrated circuits with particularly small structures. A photomask illuminated with very short-wavelength, extreme ultraviolet (EUV) radiation is projected onto a lithographic object to transfer the mask structure to the object.

[0005] The projection exposure system comprises several EUV mirrors, each with an optical surface that reflects the EUV radiation. To minimize EUV radiation losses within the projection exposure system, the EUV mirrors have an optical surface with high reflectivity for EUV radiation. The optical surface is formed by a multilayer coating system, from which the incident EUV radiation is reflected.

[0006] In addition to the projection exposure system itself, there are other optical systems that are operated in conjunction with microlithographic projection exposure systems. These include, for example, measuring devices for examining the reflectivity of EUV mirrors, devices for examining modules and subsystems, and measuring devices for examining the properties or condition of photomasks. EUV mirrors are also used in such optical systems.

[0007] Between the application of the multilayer coating system to a mirror body substrate and the subsequent commissioning of the respective EUV mirror component, there is an intermediate phase in which the EUV mirror component may be exposed to various influences. For example, the EUV mirror component may be stored, packaged, transported, or assembled. It is also possible that further processing steps may be performed on the EUV mirror component.

[0008] It has been shown that contamination or damage to the multilayer coating system can occur in this intermediate phase. Possible impairments include mechanical damage due to cutting processes (e.g. laser cutting), (chemical) layer damage due to etching media, photoresists and / or solvents, contamination due to environmental influences and / or insufficient removal of an applied layer (e.g. photoresist), particle contamination due to insufficient removal of an applied layer (e.g. photoresist), change in surface termination due to chemical interactions of the surface during a structuring process, layer roughening due to etching media, photoresists and / or solvents, diffusion of solvents and / or etching media through the EUV layer and resulting layer detachment during later use of the EUV mirror component as well as light- or particle-based radiation damage.All these influences can lead to an impairment of the multilayer coating system and thus to a reduced quality of the optical surface of the EUV mirror component.

[0009] The invention is based on the object of presenting a method for producing an EUV mirror component and an intermediate product of an EUV mirror component, which avoid these disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0010] In the method according to the invention for producing an EUV mirror component, a multilayer coating system is applied to a surface of a mirror body substrate in order to form an optical surface that is highly reflective of EUV radiation. A temporary protective coating structure is created on the multilayer coating system. The protective coating structure comprises a protective layer and a sacrificial layer arranged between the protective layer and the multilayer coating system. The temporary protective coating structure is removed before the EUV mirror component is put into operation.

[0011] The invention is based on the realization that, due to conflicting requirements, it is not entirely easy to protect the optical surface in the intermediate phase from adverse effects. While protective coatings are known in principle that can be applied to the multilayer coating system and that offer adequate protection against environmental influences, it has proven difficult to remove such protective coatings from the multilayer coating system without damaging the system. In contrast, coatings that can be removed easily and without adversely affecting the multilayer coating system generally do not offer adequate protection against the resulting stresses.

[0012] 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 stresses that occur. The fact that more aggressive process steps are necessary to remove such a protective layer can be accepted because the sacrificial layer underneath can prevent the aggressive process steps from affecting the multilayer system. Following the removal of the protective layer, the sacrificial layer can be removed using less aggressive process steps. The less aggressive process steps can be selected in such a way that the multilayer system is not impaired.

[0013] The temporary protective coating ensures that no damage to the multilayer coating system occurs during the interim phase between the application of the multilayer coating system to the mirror body substrate and the commissioning of the EUV mirror component. After removing the temporary protective coating, the EUV mirror component can be commissioned with a flawless optical surface.

[0014] The multilayer coating system can comprise alternating layers of molybdenum and silicon. Such a coating can reflect approximately 70% of the incident EUV radiation. The multilayer coating system can be optimized for the reflection of EUV radiation in the extreme ultraviolet spectral range with wavelengths between 5 nm and 30 nm, particularly with a wavelength of 13.5 nm.

[0015] The multilayer system can comprise a final layer that consists of a different material than underlying alternating layers of the multilayer structure. After removal of the temporary structure, the final layer can form the surface of the EUV mirror component. The final layer can assume a protective function during later operation of the EUV mirror component, for example to counteract rapid degradation of the multilayer system. The final layer can consist of an inorganic material. The final layer can consist of ruthenium, TiCt or rhenium, for example. The final layer can have a thickness between 1 nm and 20 nm, preferably a thickness between 2 nm and 10 nm.

[0016] The sacrificial layer can be a layer that is applied to the multilayer system. The sacrificial layer can be applied directly to the final layer of the multilayer system. The material for the sacrificial layer can be selected so that it meets one or more of the following requirements. The sacrificial layer should be removable without leaving any residue and without damaging or contaminating the multilayer system. This can be achieved in particular by a high level of purity of the sacrificial layer material. 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 low roughness in order to avoid negative influences on subsequent processing steps.

[0017] In one embodiment, the sacrificial layer is a carbon layer. The carbon layer preferably consists of at least 80%, more preferably at least 90%, more preferably at least 99.99% carbon. Percentages regarding the proportions of substances in a layer refer to 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 can therefore be expected. Carbon has the advantage that it can be removed using a hydrogen plasma. When a hydrogen plasma is used, 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 for removing the carbon layer are possible.The carbon layer may, for example, have a thickness between 1 nm and 30 nm, preferably between 2 nm and 5 nm.

[0018] Alternative materials for the construction of the sacrificial layer include: nitrides; smooth-growing, high-purity carbon compounds with a high sublimation point, such as higher acenes; carbon compounds with a low sublimation point that can be removed by heating to a temperature of less than 350 °C; metals; 2D materials, such as 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 between 10 nm and 300 nm, for example.

[0019] Possible methods for applying the sacrificial layer include sputtering, electron beam deposition, chemical vapor deposition, physical vapor deposition, atomic layer deposition, spin coating, and spray coating. Combinations of these methods are also possible. In general, the sacrificial layer should be applied in such a way that the multilayer coating system is not damaged by the application of the sacrificial layer. In particular, a temperature of 350 °C should not be exceeded.

[0020] Instead of applying the sacrificial layer to the multilayer coating system, the sacrificial layer can also be created by converting the final layer of the multilayer coating system.

[0021] In one embodiment, the sacrificial layer is produced by oxidation of the final layer. If the sacrificial layer is produced by oxidation, this has the advantage that the step of applying an additional layer for the sacrificial layer can be omitted. A further advantage can arise from the fact that an oxide of the final layer of the multilayer coating system generally has only a minor effect 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, at least a vast majority of the sacrificial layer should be removed, in particular at least 80%, preferably at least 90%, more preferably at least 95%.

[0022] It is also possible to produce a sacrificial layer with a first sub-layer and a second sub-layer. The first sub-layer, which borders on the multi-layer system, can be optimized for easy removal. The second sub-layer of the sacrificial layer can be optimized to form a suitable base for applying the protective layer. For example, the second sub-layer of the sacrificial layer can form a surface that can be easily wetted by the material of the protective layer. It is also possible for the second sub-layer to form a separating layer between the protective layer and the first sub-layer of the sacrificial layer, for example if the material of the protective layer would be aggressive to the first sub-layer of the sacrificial layer.Additionally or alternatively, the second sublayer of the sacrificial layer can be selected such that it has sufficient resistance to the deposition process used to apply the protective layer and / or to the cleaning process used to remove the protective layer. After the sacrificial layer has been created, the protective layer can be applied to the sacrificial layer. The material of the protective layer should be selected such that one or more of the following requirements are met.Stability against mechanical stress, stability against etching media, stability against photoresists and / or solvents, stability against temperatures up to 350 °C, effective diffusion barrier for oxygen and / or photoresist and / or solvents, good adhesion to the sacrificial layer, low roughness to avoid negatively affecting further processing steps, residue-free removal without damaging or contaminating the EUV layer. The thickness of the protective layer can, for example, be between 0.1 pm and 10 pm.

[0023] In one embodiment, the protective layer is applied as a protective lacquer having appropriate properties. In particular, the protective layer can be formed by a protective lacquer in the form of a photoresist. In one embodiment, the protective lacquer has good layer cohesion, so that the protective layer can be peeled off the sacrificial layer similar to a film. In the case of a protective layer in the form of a protective lacquer, the layer thickness can, for example, be between 1 μm and 10 μm.

[0024] In an alternative embodiment, the protective layer is formed by applying silicon dioxide SiO2. Silicon dioxide has sufficient resistance to fulfill the desired protective function. To remove a layer of silicon dioxide, an HF vapor deposition process, which has high selectivity for the removal of silicon dioxide, can be used, for example. In the case of a protective layer made of silicon dioxide, the layer thickness can be between 0.1 pm and 0.3 pm, for example. 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 single process.In general, the protective layer and the sacrificial layer should be removed in such a way that one or more of the following requirements are met. Damage to the multilayer coating system should be avoided. The protective layer and the sacrificial layer should be removed completely so that no contamination remains on the surface of the multilayer coating system. Increased particle contamination or roughening of the surface of the multilayer coating system should be avoided. A surface temperature of 350 °C should not be exceeded by using suitable non-thermal processes or by employing suitable cooling of the substrate.

[0025] Methods that can generally be considered for removing the protective layer and / or the sacrificial layer are: dry chemical methods such as the use of HF vapor, CF4, CHF3, etc.; plasma cleaning, for example using H plasma and / or O plasma; cleaning with an ion beam source; wet chemical cleaning; laser cleaning; use of CO2 rays; annealing at temperatures below 350 °C and / or suitable substrate cooling; peeling off the protective layer as a film. It is possible to combine these cleaning methods and / or apply them one after the other when removing the protective layer and / or the sacrificial layer.

[0026] If the protective layer is formed by a protective lacquer, it may be advantageous to use a wet-chemical process to remove 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 processes generally have the advantage that particles and contaminants, both on the protective layer and inside the protective layer, are reliably removed. The solvent can be selected so that it does not attack the underlying sacrificial layer.

[0027] The use of a dry-chemical process for removing the protective layer may be appropriate if the protective layer consists of silicon dioxide. In particular, the protective layer can be removed using an HF vapor process, which exhibits high selectivity for removing silicon dioxide. If the protective layer is completely dissolved in this way, particles and contaminants both on and within the protective layer can be removed.

[0028] If a contamination layer has formed on or within the protective layer structure, for example due to particle deposition or oxidation, it can be removed before removing the underlying layer. One possible method for removing the contamination layer is the use of oxygen plasma.

[0029] The removal of the protective layer can be followed by the removal of the sacrificial layer. A gentle process is recommended for this in order to avoid damage to the multilayer system. A generally suitable process, for example, is the use of a hydrogen plasma (H* plasma or H' plasma). This is particularly true if the sacrificial layer is a carbon layer. Even if the sacrificial layer is created by oxidation of the final layer of the multilayer system, the removal can be carried out using a hydrogen plasma. If necessary, this can be combined with a physical etching process, such as the prior application of a noble gas plasma. The noble gas plasma can be, for example, a neon plasma, an argon plasma or a krypton plasma.

[0030] The application of the multilayer coating system to the mirror body substrate can take place in a process chamber under vacuum conditions. The creation of the sacrificial layer of the temporary protective layer structure according to the invention can follow this process without the EUV mirror component leaving the process chamber. Maintaining the vacuum between the application of the multilayer coating system and the creation of the sacrificial layer reduces the risk of contamination.

[0031] The vacuum can also be maintained until the protective layer of the temporary protective coating structure has been applied. In one embodiment, the protective layer is created in the same process chamber as the multilayer coating system.

[0032] The process can be carried out in such a way that the EUV mirror component is not subjected to any further processing steps in the intermediate phase between the creation of the temporary protective layer structure and its removal. The primary function of the protective layer structure can be to protect the optical surface during transport and storage.

[0033] 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 in which material is removed from the multilayer structure and / or from the substrate of the EUV mirror component. For example, a processing step can be carried out in which a structuring is created in the optical surface of the EUV mirror component. The structuring can be created using a lithography process. 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 created. The processing steps can be carried out in the regions of the optical surface in which the photoresist was locally removed.

[0034] Additionally or alternatively, one or more of the processing steps listed below can be carried out. Mechanical processing can be carried out, for example to edge the optical surface and / or to process the substrate contour. Thermal treatment can be carried out, 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 carried out without a vacuum. Chemical treatment is also possible, for example for the purpose of structuring, which can be carried out wet-chemically, from the gas phase or by ion beam etching. In one embodiment, the chemical treatment is carried out in combination with a lithographic process. Another variant is irradiation with ions, with electrons, with UV radiation or with X-rays.

[0035] The function of the protective layer structure according to the invention can be to protect the optical surface during the processing steps.

[0036] In the case of structuring using a photoresist, the photoresist can also 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 structure. The photoresist can then be removed in a single process step together with the protective layer. It is also possible to remove the photoresist separately from the protective layer in a preceding process step.

[0037] The structuring can serve to divide a surface continuously covered with a multilayer coating system into a plurality of mirror elements. The processing steps can be used to remove parts of the mirror body substrate in order to create solid-state joints within the mirror body substrate, so that each of the mirror elements is articulated to a main body of the mirror body substrate via a solid-state joint. The mirror body substrate can be made of silicon, in particular monocrystalline silicon. The function of the temporary protective layer structure according to the invention can be to offer protection to the optical surface—insofar as it remains intact—during these processing steps.An EUV mirror component comprising a plurality 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 microlithographic projection exposure system.

[0038] A sequence of process steps is also possible, in which the processing steps for dividing the optical surface into a plurality of mirror elements are carried out first, and then the temporary protective layer structure is created. This opens up the possibility of the temporary protective layer structure protecting the outer surfaces of the mirror elements that lie between the optical surface and the solid-state joints.

[0039] In one embodiment, the temporary protective layer structure is produced on an optical surface that is not subjected to any further structuring, so that the EUV mirror component has a uniform and continuous optical surface during later use. Such EUV mirrors can be used in an optical system, such as a projection objective of a microlithographic projection exposure system, to deflect and shape an EUV beam path. These mirrors often have high requirements for the geometric shape of the optical surface. In order to meet these requirements, the mirror body can be made of a material whose thermal expansion coefficient has a zero crossing temperature. An example of such a material is a titanium silicate glass known as ULE™ (Ultra Low Expansion) or ZERO-DUR™.In such an embodiment, the temporary protective layer structure can primarily serve to protect the optical surface during transport and storage, as well as during steps other than structuring the optical surface. These include, for example, bonding steps, in which the optical surface is protected from adhesive vapors by the temporary protective layer structure.

[0040] In general, metallic materials, monocrystalline materials, or glass can also be considered as materials for the substrate of the mirror body. In one embodiment, the mirror substrate material is silicon, in particular monocrystalline silicon.

[0041] The temporary protective layer structure can be removed in a separate process before the EUV mirror component is mounted in an optical system. With this procedure, there is a risk that damage or contamination could occur on the optical surface of the EUV mirror component in the phase between the removal of the temporary protective layer structure and assembly. In one embodiment, the sacrificial layer is therefore only removed after the EUV mirror component has been mounted in the optical system. This is particularly useful if the sacrificial layer is removed using a hydrogen plasma, to which the multilayer system may be exposed anyway during later operation. The protective layer can be removed in a previous step before the EUV mirror component is mounted.The possibility of removing both the sacrificial layer and the protective layer after assembly of the EUV mirror component is also included.

[0042] The invention also relates to an intermediate product of an EUV mirror component. A multilayer coating system is applied to one surface of the mirror body substrate, forming an optical surface highly reflective of EUV radiation. A temporary protective coating structure is arranged on the multilayer coating system. The protective coating structure comprises a protective layer and a sacrificial layer arranged between the protective layer and the multilayer coating system.

[0043] The disclosure includes further developments of the method with features described in connection with the EUV mirror component intermediate product according to the invention. The disclosure includes further developments of the EUV mirror component intermediate product with features described in connection with the method according to the invention.

[0044] The invention is described below by way of example with reference to the accompanying drawings using advantageous embodiments. They show:

[0045] Fig. 1: a microlithographic projection exposure system;

[0046] Fig. 2: a section of an EUV mirror component;

[0047] 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;

[0048] Fig. 5: the view according to Fig. 2 in a fourth state of the EUV mirror component;

[0049] Fig. 6-8: various intermediate stages in the production of a facet mirror;

[0050] Fig. 9: the view according to Fig. 7 in an alternative

[0051] Embodiment of the invention;

[0052] Fig. 10: a representation of a process sequence according to the invention;

[0053] Fig. 11: the view according to Fig. 10 in an alternative

[0054] Embodiment of the invention.

[0055] Fig. 1 schematically illustrates a microlithographic EUV projection exposure system. The projection exposure system comprises an exposure beam source 14, an illumination system 10, and a projection lens 22, which are operated together in a vacuum chamber 23.

[0056] 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 beam emanating from the exposure beam source 14 is focused into an intermediate focal plane 16 by a collector 15. Exposure beam emanating from the intermediate focal plane 16 is guided into an object plane 12 by the illumination system 10, so that an object field in the object plane 12 is illuminated with uniform radiation intensity.

[0057] The illumination system 10 comprises a deflecting 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 second facet mirror 19 images the facets of the first facet mirror 18 onto the object plane 12.

[0058] A photomask 13 is arranged in the object plane 12 and is imaged into an image plane 21 via a plurality of mirrors M1-M6 of the projection lens 22. A structure formed on the photomask 13 is transferred to a radiation-sensitive layer of a wafer 20 arranged in the image plane 21. The photomask 13 is suspended from a first scanning device 24, and 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.

[0059] Each of the EUV mirrors 17, 18, 19, M1-M6 in Fig. 1 is provided with a multilayer coating system that 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 mirror M1. Fig. 2 shows an enlarged sectional view of a section of mirror M1.

[0060] The mirror M1 comprises a mirror body 30 made of a mirror substrate material with ultra-low thermal expansion ("ultra-low expansion material"). Examples of such materials are a titanium silicate glass sold under the name ULE™ or ZERODUR™, both of which have a so-called zero crossing temperature (= "zero crossing temperature"). At this zero crossing temperature, which for example for ULE™ is around 30 °C, the thermal expansion coefficient has a zero crossing in its temperature dependence, in the vicinity of which no or only negligible thermal expansion of the mirror substrate material occurs. A multilayer coating system 31 with alternating layers 32 made 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 top layer 33 that exhibits good resistance to influences occurring during operation of an EUV mirror. The top layer 33 can be somewhat thicker than the remaining layers 32 of the multilayer system and can be, for example, between 1 nm and 20 nm thick. The top layer 33 can be made of, for example, ruthenium, TiCt, or rhenium.

[0061] In Fig. 2, the EUV mirror Ml is shown in the state in which it is used in the microlithographic projection exposure system. The final layer 33 of the multilayer system 31 forms the surface of the EUV mirror Ml during operation of the projection exposure system.

[0062] The EUV mirror Ml also has the state according to Fig. 2 during production at a time immediately after the multilayer coating system 31 has been applied to the mirror body 30. Between this time and the commissioning of the EUV mirror Ml in the projection exposure system there is an intermediate phase which can extend over a longer period of time. In the intermediate phase the EUV mirror Ml 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 coating system 31 would be exposed to direct environmental influences, which would be associated with a risk of contamination or damage to the multilayer coating system 31. The invention proposes protecting the multilayer coating system 31 during the intermediate phase with a protective coating structure 36, see Figs. 3, 4.The protective layer structure 36 comprises a sacrificial layer 34 and a protective layer 35, which are applied successively to the surface of the EUV mirror. The sacrificial layer 34 is optimized such that it forms a good basis for the application of the protective layer 35 and that it can be removed easily and, in particular, without leaving any residue before the EUV mirror M1 is put into operation, without damaging the final layer 33 of the multilayer system 31. The protective layer 35 is optimized for good protective action 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 before commissioning of the EUV mirror M1, this can be accepted because the underlying sacrificial layer 34 prevents the aggressive steps from having an effect on the multilayer coating system 31.

[0063] In Fig. 3, the EUV mirror Ml is shown in a state in which the sacrificial layer 34 has been applied to the final layer 33 of the multilayer system 31. The sacrificial layer 34 is applied in the same process chamber in which the final layer 33 of the multilayer system 31 was previously applied. Both the final layer 33 and the sacrificial layer 34 are applied under vacuum, with the vacuum being 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.

[0064] The application of the protective layer 35 can be carried out in a separate process chamber. A state of the EUV mirror M1 in which the complete protective layer structure 36 with the sacrificial layer 34 and the protective layer 35 has been applied is shown in Fig. 4.

[0065] Before commissioning the EUV mirror M1, 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 the state it had after exposure to the aggressive process steps used to remove the protective layer 35. In particular, the sacrificial layer may have an uneven and / or damaged surface that is unsuitable for the application of further layers.

[0066] After the remaining sacrificial layer 34 has been removed using a gentler method, the EUV mirror Ml again has the state shown in Fig. 2. The EUV mirror Ml is ready to be put into operation in the microlithographic projection exposure system.

[0067] Figs. 6-8 illustrate various stages in the manufacture of a component for the first facet mirror 18 or the second facet mirror 19 of the microlithographic projection exposure apparatus of Fig. 1. A substrate body 37 is provided, which consists of monocrystalline, polycrystalline, or amorphous silicon. A multilayer coating system 31 corresponding to Fig. 2 is applied to a surface of the substrate body 37.

[0068] A protective layer structure 36 is applied to the multilayer coating 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 in a subsequent processing step. Fig. 7 shows a state in which material has been removed between individual EUV mirror components 40, so that the EUV mirror components 40 are separated from one another right 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 schematically shown solid-state joint 39. The protective layer structure 36 ensures that the multilayer coating system 31 is not damaged in the regions in which it is intended to form the optical surface of the EUV mirror components 40.

[0069] Each of the facet mirrors 18, 19 is assembled from several components of the type shown in Fig. 7. Before commissioning a facet mirror 18, 19 in the microlithographic projection exposure system, the protective layer structure 36 is removed so that the EUV mirror components 40 obtain their final state shown in Fig. 8.

[0070] Fig. 9 shows an alternative embodiment in which the multilayer coating system 31 is applied only after suitable structuring of the substrate body 37. A protective coating structure 36 is applied to the multilayer coating system 31, which protects the optical surface and the side surfaces of the EUV mirror components 40.

[0071] An exemplary embodiment of a protective layer structure 36 according to the invention is explained with reference to Fig. 10. A schematic timeline T shows the order in which layers are added to and removed from the surface of the mirror body. In a first step, a carbon layer with a thickness of between 2 nm and 5 nm is applied to the final layer 33 of the multilayer system 31 by gas phase deposition. The carbon layer forms a sacrificial layer 34 in the sense of the invention. The subsequent step, in which the protective layer 35 is applied, takes place in a different process chamber. During transport there, the EUV mirror in the exemplary embodiment shown is exposed to an oxygen-containing atmosphere, which has the result that the sacrificial layer 34 can oxidize and that impurities are deposited. A corresponding contamination layer 41 on the sacrificial layer 34 is shown in Fig. 10.There are other embodiments without such a contamination layer.

[0072] The protective layer 35 is applied to the contamination layer 41. In this exemplary embodiment, the protective layer 35 is formed by a protective lacquer applied by spin coating. The protective lacquer has a thickness between 1 μm and 10 μm.

[0073] A photoresist 42 is again applied to the protective layer 35 by spin coating. The photoresist 42 can be selectively exposed to define areas for subsequent structuring.

[0074] Before the EUV mirror is put into operation in the projection exposure system, the layers are removed one after the other until the final layer of the multilayer system 31 is exposed. First, solvents are used to remove the photoresist 42 and the protective resist 35 using 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 to this. The sacrificial layer 34 is only removed after the EUV mirror has been installed in the projection exposure system, by exposing the surface of the EUV mirror to a hydrogen plasma. The projection exposure system with the EUV mirror is then ready for use.

[0075] Carbon, as the material of the sacrificial layer 34, has a lower surface energy than metals, so that good coverage of the multilayer coating system 31 by the final layer 33 can be expected. This promotes residue-free removability of the sacrificial layer 34 from the final layer 33. The wet-chemical processes for removing the photoresist 42 and the protective layer 35 facilitate the removal of particles and contamination both on and in the layers. By using exclusively chemical processes and no physical etching processes to remove the layers, the material removal is very selective.

[0076] In the embodiment according to Fig. 11, the sacrificial layer 34 is produced by oxidizing the final layer 33 of the multilayer system 31. An oxide layer with a thickness of a few nanometers is formed. A protective layer 35 made of silicon dioxide, which is between 100 nm and 300 nm thick, is applied to the oxide layer 34 by means of gas phase deposition. During subsequent storage of the EUV mirror, a contamination layer 41 can form on the protective layer 35. The photoresist 42 for structuring the surface is applied to the contamination layer 41 by means of spin coating. The thickness of the photoresist layer is again between 1 pm and 10 pm.

[0077] Before the EUV mirror is put into operation in the projection exposure system, the layers are removed. The photoresist 42 is again removed using solvents. The contamination layer 41 is removed using an oxygen plasma. The protective layer of silicon dioxide can be removed using RF vapor. To remove the oxide layer that forms the sacrificial layer 34, a hydrogen plasma, for example, can be used. Alternatively, the sacrificial layer can be removed by physical sputtering (e.g., noble gas plasma) or by using RF vapor.

[0078] This embodiment has the advantage that no separate deposition of the sacrificial layer 34 is required. By removing the protective layer structure 36 using dry-chemical processes, the multilayer coating system 31 is protected. By completely dissolving the protective layer 35 by applying HF vapor, contamination and particles both on and in the layer can be reliably removed. By using complementary deposition and removal processes, separation of the functionalities is facilitated. If the sacrificial layer 34 is only incompletely removed, this can be accepted because small residues of the oxide of the final layer 33 do not significantly impair the reflectivity of the multilayer coating system 31 for EUV radiation.

Claims

Patent claims 1. 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 which is highly reflective for EUV radiation, wherein a temporary protective layer structure (36) is produced on the multilayer coating 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 coating system (31), and wherein the temporary protective layer structure (36) is removed before the EUV mirror component is put into operation, wherein the sacrificial layer (34) is a layer which is produced by oxidation of a layer of the multilayer coating system (31).

2. The method according to claim 1, wherein the multilayer system (31) comprises a final layer (33) which consists of a different material than underlying alternating layers (32) of the multilayer structure (31).

3. The method according to claim 1 or 2, wherein the sacrificial layer (34) is a layer applied to the multilayer coating system (31).

4. The method of claim 3, wherein the sacrificial layer (34) is a carbon layer.

5. 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.

6. The method according to claim 1 or 2, wherein the sacrificial layer (34) is a layer produced by oxidation of a layer of the multilayer coating system (31).

7. Method according to one of claims 1 to 6, wherein the protective layer (35) is applied as a protective varnish.

8. The method of claim 7, wherein the protective resist is a photoresist.

9. Method according to one of claims 1 to 6, wherein the protective layer (35) is formed by silicon dioxide.

10. Method according to one of claims 1 to 9, wherein a temperature of 350 °C is not exceeded during removal of the protective layer structure (36).

11. The method according to any one of claims 1 to 10, wherein the EUV mirror component (M1-M6, 40) is subjected to a processing step after the production and before the removal of the temporary protective layer structure (36), with which material is removed from the multilayer structure (31) and / or from the mirror body substrate (37).

12. The method according to claim 11, wherein a surface continuously covered with a multilayer coating system (31) is divided into a plurality of mirror elements (40).

13. EUV mirror component intermediate product with a multilayer coating system (31) applied to a surface of a mirror body substrate (30, 37), which forms an optical surface that is highly reflective for EUV radiation, wherein a temporary protective layer structure (36) is arranged on the multilayer coating 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 coating system (31), and wherein the sacrificial layer (34) is a layer produced by oxidation of a layer of the multilayer coating system (31).

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