Optical arrangement, semiconductor technology system and methods for removing contamination

Abstract

The invention relates to an optical arrangement (131) comprising: an optical element (102) for reflecting EUV radiation, and a cleaning device (132) for providing a cleaning gas (133) for removing contaminants (130) present in the region of the optical element (102). To protect an optical surface (102a) of the optical element (102) from the contaminants (130) removed by the cleaning device (132), the optical arrangement (131) has at least one shield (136') spaced apart from the optical surface (102a, 103a). The invention also relates to a semiconductor technology system comprising at least one such optical arrangement (131), and to a method for removing contaminants (130) present in the region of an optical element (102) for reflecting EUV radiation (124).

Description

Background of the invention The invention relates to an optical arrangement comprising: an optical element for reflecting EUV radiation, and a cleaning device for providing a cleaning gas for removing contaminants present in the region of the optical element. The invention also relates to a semiconductor technology system, in particular an EUV lithography system, which has at least one such optical arrangement. The invention further relates to a method for removing contaminants, comprising: providing a cleaning gas for removing the contaminants. For the purposes of this application, a semiconductor technology system is understood to be an optical system for lithography, i.e., an optical system that can be used in the field of lithography. In addition to a lithography system used for the production of semiconductor devices, the system may, for example, be an inspection system for inspecting a photomask (hereinafter also referred to as a reticle) used in a lithography system, for inspecting a semiconductor substrate to be structured (hereinafter also referred to as a wafer), or a metrology system used for measuring a lithography system or parts thereof, for example, for measuring a projection system. The semiconductor technology system operates using useful radiation in the form of EUV radiation. EUV radiation is defined as radiation in a wavelength range between approximately 5 nm and 30 nm, for example, at 13.5 nm. Since EUV radiation is strongly absorbed by most known materials, it is typically guided through the semiconductor lithography system using reflective optical elements. Due to the required resolution of semiconductor technology systems, especially EUV lithography systems, it is necessary that the optical elements have as few contaminants or impurities, especially particulate contamination, as possible on their optical surfaces in order to avoid limitations in image quality caused by impurities. It has been shown that, despite the arrangement of the optical elements within housings of a projection imaging system, particle contamination cannot be completely ruled out, especially if the particles are distributed along a beam path of the EUV radiation used for imaging. The particles located inside the housings can, for example, settle on the inner walls of the housings or on or around the optical elements. Particles passing through the beam path can also block the EUV radiation and therefore result in a loss of transmission. In particular, particles in the form of tin particles, which originate within the radiation source, can enter the illumination system via an intermediate focus between the radiation source and the illumination system. The tin particles can travel along the beam path through the illumination system to the mask and deposit there. These deposited tin particles on the mask can cause serious problems with imaging onto the wafer. Since there is only a very limited direct line of sight between the intermediate focus and the dynamic gas lock of the reticle, most of the tin particles within the illumination system must "hop," i.e., undergo elastic collisions, to reach the reticle. Furthermore, it has been shown that not all tin particles present in the illumination system reach the mask; rather, a significant number of tin particles remain on the surfaces of the illumination system and are deposited, for example, on the optical surfaces of the optical elements or elsewhere, leading to a loss of transmission. Some of the tin particles in the illumination system also react with an EUV-induced hydrogen plasma present there, forming volatile tin-hydrogen compounds (stannanes), a process also known as hydrogen-induced outgassing. These volatile tin-hydrogen species reach the optical surfaces of the optical elements in the illumination system and are deposited on these surfaces as tin contamination, resulting in a significant reduction in reflectivity, which amounts to approximately [missing information] over the entire lifetime of the illumination system.This can amount to 10-20% and results in a significant loss of productivity. In addition to hydrogen-induced outgassing, another reaction occurs with tin particles, known as "cold spitting": Due to the presence of a hydrogen plasma during the operation of the semiconductor technology system, the larger tin particles become loaded with hydrogen. As a means of relaxation, these larger tin particles expel smaller tin particles, which contribute significantly to the tin contamination in the illumination system and especially on the reticle. For details on the "cold spitting" of tin particles in a hydrogen plasma environment, see the dissertation "Behaviour of nanoparticles on surfaces exposed to EUV environments" by D. Shefer, Eindhoven University of Technology, 2023. The measures proposed to prevent particle contamination do not completely suppress the flow of particles to the optical surfaces of the optical elements, such as the mirrors and reticles, as well as to other surfaces. Therefore, these measures only function satisfactorily for a limited period during the operating life of the semiconductor technology system. However, the number of particles deposited in the illumination system (on the surfaces of the housing or non-optical elements and on the surfaces of the mirrors) increases steadily with increasing operating time, and these deposited particles represent an additional source from which particles can migrate to the reticles.It has been shown that after a long operating period of the semiconductor technology system, severe contamination of the lighting system can occur in comparatively short periods of time, which in the worst case necessitates a replacement of the entire lighting system. It is therefore advantageous to remove surface contaminants, especially particulate contaminants such as tin particles, from semiconductor technology equipment. This can be achieved through cleaning using a cleaning gas or one or more cleaning gas streams. German patent application DE 10 2008 028 868 A1 describes an optical assembly for microlithography, comprising at least one optical element with an optical surface. A cleaning device is used to clean the optical surface with atomic hydrogen. A deposition device is used to apply a carbon-containing layer to the optical surface to simplify cleaning: When exposed to a cleaning medium, the carbon-containing layer generates carbon-containing gases that detach foreign particles adhering to the optical surface to be cleaned. The cleaning device can have a housing that includes a jacket section with a sealing profile which rests against the optical surface to be cleaned and seals an interior of the housing from the environment. German patent application DE 10 2009 012 091 A1 describes an optical arrangement comprising a cleaning unit for directing a cleaning gas jet containing atomic hydrogen onto the optical surface of an optical element. The optical arrangement also includes a shield arranged on the optical element with a guide surface for directing atomic hydrogen from the cleaning gas jet that does not strike the optical surface towards the optical surface. EP 4318133 A1 describes a shielding system for use in a surface treatment process of a component of a lithography system. The shielding system can be arranged between a plasma source and a support device for holding the component to be treated, in order to shield at least part of the component's surface, which typically has bumps. DE 10 2011 079 450 A1 describes an optical arrangement in which, to improve the suppression of surface degradation of an optical element, a heating device for heating the optical element and / or a cleaning head for generating a gas stream containing activated hydrogen directed at the surface are provided. At least one gaseous component can be added to a residual gas atmosphere in which the optical element is arranged in order to suppress surface degradation by forming a plasma on the surface. US Patent 8,419,862 B2 describes a method for at least partially removing a contamination layer from the optical surface of an EUV reflective optical element. In this method, a cleaning gas jet is directed at the contamination layer to remove material from it. The cleaning gas in the jet can be atomic hydrogen generated in a cleaning gas generator. The generator may include a heated filament to produce the atomic hydrogen. A similar device for generating a cleaning gas in the form of atomic hydrogen is described in DE 10 2015 219 939 A1. DE 10 2009 045 170 A1 describes the conversion of contaminants that accumulate on a reflective optical element during the operation of an EUV lithography device into volatile compounds by supplying the optical element with, among other things, atomic or molecular hydrogen. DE 10 2016 204 904 A1 describes the supply of gaseous hydrogen in the form of a gas mixture with at least one inert gas into a vacuum chamber of an optical arrangement, whereby the supply can take place during operation of the optical arrangement or during a break in operation. DE 10 2022 212 168 A1 describes an EUV optical module with a gas source that provides hydrogen, but also volatile metal oxides or metal fluorides. DE 10 2009 001 488 A1 describes the removal of contaminants from an optical surface using activated hydrogen, whereby a hydrocarbon monomer is simultaneously deposited on the optical surface to form a polymerized protective layer. DE 10 2017 213 176 A1 describes an optical element with a substrate onto which a protective layer is applied to protect the substrate from a chemical reaction with a hydrogen plasma; this layer may contain carbon in the form of diamond. Object of the invention The object of the invention is to provide an optical arrangement, a semiconductor technology system and a method for removing contamination, in which the contamination can be removed as efficiently as possible. Subject matter of the invention This problem is solved by an optical arrangement of the type mentioned above, which, in order to protect an optical surface of the optical element from the contaminations removed by means of the cleaning device, has at least one shield spaced away from the optical surface. The inventors discovered that contaminants, particularly in the form of the tin contaminants or tin particles described above, often accumulate in localized concentrations even outside the optical surface of the optical element. To remove these contaminants, a cleaning gas is provided, or the contaminants are brought into contact with the cleaning gas and thereby transferred into the gas phase. To prevent the contaminants transferred into the gas phase during cleaning from depositing on the optical surface, the optical arrangement includes at least one shield positioned away from the optical surface. This shield protects the optical surface from the contaminants transferred into the gas phase and increases cleaning efficiency by preventing cross-contamination. The shield is spaced away from the optical surface; that is, it is not in contact with the optical surface.in contact with a reflective coating provided there. In one embodiment, the cleaning device has at least one cleaning head for providing the cleaning gas in the form of a cleaning gas stream, wherein the cleaning head is directed to a position outside the optical surface of the optical element, in particular to a position adjacent to the optical surface of the optical element. In this embodiment, a cleaning gas stream is generated by means of at least one cleaning head, which is not directed towards the optical surface. As described above, the cleaning gas stream serves to remove contaminants from surfaces or surface areas located outside the optical surface of the optical element and where a high concentration of contaminants occurs. The cleaning head, more precisely a nozzle of the cleaning head, and thus the cleaning gas stream, can be directed towards a position where a heavily contaminated surface area is located. Alternatively or additionally, the cleaning gas stream can also be directed such that the contaminants transferred into the gas phase are transported in a predetermined direction, for example, towards a getter surface with a gas-binding material (su).The position towards which the cleaning gas stream is directed may also include a getter surface. In this case, the cleaning gas stream is typically guided along a contaminated surface area. The cleaning head can be configured to generate a cleaning gas stream containing atomic hydrogen and, for this purpose, may include, for example, a heating filament, as described in US 8,419,862 B2, which is incorporated by reference in its entirety into this application. It is also possible for the cleaning head to be configured to generate a cleaning gas stream forming a hydrogen plasma, i.e., containing predominantly hydrogen ions. Such a cleaning gas stream typically contains atomic hydrogen in addition to hydrogen ions. With the aid of activated hydrogen H*, i.e., hydrogen ions, hydrogen radicals, and / or hydrogen in an excited electronic state, contaminants in the form of tin contamination, e.g., by the chemical reaction Sn(S) + H* → SnH4(g), can be converted into gaseous species in the form of stannanes. In one embodiment, the shield is arranged at least partially, and in particular completely, between the cleaning head and the optical surface, with the shield preferably surrounding an interior space in which the cleaning head provides the cleaning gas flow. In this case, the shield is typically designed as a housing that is open towards the position toward which the cleaning head is directed, in order to supply the cleaning gas flow to this position where the contaminants have accumulated. The housing may be arranged at a small distance from the surface on which the contaminants have accumulated, but it is also possible for the shield to be in contact with the surface to be cleaned. In this case, the shield is brought into contact with the optical element outside the optical surface, for example, via a seal or the like.In this case, the shielding is typically located outside the beam path of the optical element, i.e., it does not usually obstruct the beam path. In a further development of this embodiment, the shield features an extraction system for removing the contaminants and cleaning gas removed by the cleaning device from the interior. This extraction system removes the contaminants from the interior, preventing them from reaching the optical surface. Alternatively or additionally, the contaminants can be bound to the inside of the shield using getter surfaces, which can be formed, for example, as a coating on the inside of the shield. In a further embodiment, the shielding at least partially, and in particular completely, covers the optical surface, wherein a gap is formed between the shielding and the optical surface, at least section by section, preferably having a maximum width of 1 cm or less, and particularly preferably 0.5 cm or less. In this case, the shielding, which is spaced from the optical surface, is arranged at least section by section at a comparatively small distance in front of the optical surface. The shielding here covers not only the optical surface but also a beam path in which EUV radiation strikes or is reflected by the optical surface, at least partially, and in particular completely. The degree of coverage can be, for example, more than 30%, more than 40%, more than 60%, or more than 80%. In this case, the shielding can be, in particular, plate-shaped. Alternatively, the shielding is arranged only in a typically outer, e.g., ring-shaped area at a small distance from the optical surface, while in the remaining area it has a greater distance to avoid contact with the optical surface during assembly. In this embodiment, the outer, ring-shaped area has a radial length preferably more than 1 cm, particularly preferably more than 2 cm, and a distance to the optical surface of 0.5 cm or less, preferably 0.3 cm or less. The outer, typically ring-shaped area usually extends along the edge of the optical surface or lies outside the optical surface, i.e., the outer area of ​​the shielding projects laterally beyond the optical surface. In this case, the shield is typically positioned in front of the optical element only during a downtime for cleaning. During normal operation of the optical system, the shield is usually removed. For this purpose, the shield can be detachably attached to a support that is permanently located near the optical element. Alternatively, the support for the shield can be positioned near the optical element during downtime for cleaning. In a further development of this embodiment, the optical arrangement includes a purge device for supplying a purge gas stream into the space between the shield and the surface. The purge gas stream serves to suppress the penetration of volatile contaminants formed during cleaning, in particular stannans, into the space between the shield and the optical surface or the supporting structure of the optical element or mirror module. In a further embodiment, the optical arrangement comprises at least one getter surface for binding the contaminants removed by the cleaning device. The getter surface is preferably formed on the inside of an enclosure that encapsulates a beam path of the optical arrangement, and / or on the inside of the shield surrounding the interior. The getter surface comprises at least one material suitable for binding the volatile contaminants, in particular stannanes. The getter material can, for example, be selected from the group consisting of: Ru, Ni, NiP, Pt, Rh, Ir, etc. The getter surface can be produced by applying the getter material as a coating to the inside of the enclosure and / or the inside of the shield.Typically, a significant portion of the volatile contaminants can be removed by the vacuum pumping system of the semiconductor technology facility. However, a considerable amount of contaminants is also usually deposited or trapped on the getter surfaces. It is advantageous for the getter surfaces to be as large as possible, ideally covering almost 100% of the inside of the enclosure or shielding, which can be achieved through a suitable coating. As described above, it is possible to direct the cleaning gas flow so that the volatile contaminants are transported towards a getter surface, but this is not strictly necessary. Another aspect of the invention relates to a semiconductor technology system, in particular an EUV lithography system, comprising: a radiation source for generating EUV radiation, and at least one optical arrangement configured as described above. The optical element of the optical arrangement can, in particular, be an optical element of the illumination system of an EUV lithography system, for example, a faceted mirror, in particular a field faceted mirror, a pupil faceted mirror, or a mirror operated under grazing incidence. However, it is also possible that the optical element is arranged in the projection system of the EUV lithography system or that the optical element is the mask.The cleaning device, more precisely the cleaning head(s), is preferably arranged in the area of ​​the optical element, for example around and / or behind the optical element. For efficient cleaning, the direction and / or flow rate of the cleaning gas can be suitably selected. In one embodiment, the semiconductor technology system is designed to remove contaminants during an operational break, with the radiation source preferably being active during this break. It is possible to use the radiation source for contaminant removal during the operational break, either in addition to or as an alternative to the cleaning heads. For example, during the operational break, the radiation source can selectively induce or accelerate "cold spitting" of particulate contaminants adhering to surfaces—that is, the emission of smaller, nanoscale particles from larger, microscale particles—thereby removing the contaminants or transferring them into the gas phase. In this way, the "cold spitting" that occurs during the operation of the semiconductor technology system can be reduced.In a cleaning operation designed for this purpose, a cleaning gas can be supplied by the cleaning device, and a hydrogen plasma can be generated by the radiation source. This plasma is more powerful, at least in areas with a high concentration of contamination, than that produced during the operation of the semiconductor technology system. For this purpose, the cleaning device can, for example, increase the pressure of the supplied cleaning gas, e.g., in the form of molecular hydrogen, and / or the flow or flow rate of the hydrogen globally and / or locally. The local increase can also be achieved, for example, by the cleaning head(s). In this way, particularly critical areas of surfaces can be cleaned where tin particles generated by "cold spitting" can directly reach the mask. The radiation source used to generate EUV radiation can also be operated to produce a stronger hydrogen plasma at the surfaces to be cleaned. This can be achieved, for example, by appropriately adjusting or modifying the tin plasma of the radiation source that generates the EUV radiation, or by changing the orientation of the radiation source, such as directing the EUV radiation away from the center of the field facet mirror and towards areas with heavy tin contamination. It is possible to monitor the amount of contaminants, such as tin particles, reaching the mask during downtime or cleaning. A specially designed cleaning mask can be used to record the number of tin particles during cleaning, or a wafer specifically designed for particle detection can be used, positioned near the mask or mask holder, for example, near a gas lock. If the inspection reveals that the contamination rate in the area of ​​the mask has been sufficiently reduced during cleaning, the cleaning process can be stopped during downtime. It is generally advantageous to protect the optical surface(s) from contaminants removed during cleaning by the cleaning equipment using the shielding described above. However, if cleaning is performed immediately before replacing an optical element or mirror, it is not strictly necessary to protect the mirror from the contaminants generated during cleaning. It is also possible to perform surface cleaning during mirror replacement or servicing, i.e., without the mirrors being present in the semiconductor equipment during cleaning. In this case, the semiconductor equipment has holes in the positions of the mirrors. These holes can be covered for cleaning using dummy mirror elements, which may, for example, have getter surfaces. Another option for removing contaminants during a downtime is to clean the optical elements, at least locally, under ambient conditions, i.e., at atmospheric pressure. In this case, the illumination system can remain in the semiconductor technology facility or be removed from the facility during servicing, or the mirrors can be replaced. Cleaning can also be achieved by generating a local plasma, typically a hydrogen plasma. For this purpose, an atmospheric pressure plasma source designed to generate an argon plasma with the addition of oxidizing or reducing gases can be used, for example, the PlasmaPen PP 1010 plasma source (see "https: / / wernerwirth.com / komponentenschutz / verarbeitungstechnik / plasmatechnologie / "). Plasma cleaning can also be combined with vacuum extraction or...a vacuum cleaner that pumps out the contaminants, for example in the form of the tin particles and / or stannans released during "cold spitting". It is also possible to perform plasma cleaning on components or structural parts of the lighting system during a repair, i.e., when the optical elements in the form of mirrors are removed from their respective structural parts and the structures or structural modules or parts thereof are placed in a plasma cleaning system provided for this purpose. In all the cases described above, the removal rate and / or the cold spitting rate of contaminants can be increased by adding reactive species to the hydrogen plasma, for example, in the form of fluorine, bromine, oxygen, etc. The rate can also be increased by thermal treatment, in particular by increasing the temperature of the contaminated surface areas and / or by alternating treatment with plasma and other reactive species (e.g., precursor-cleaning-precursor-cleaning, etc.). For cleaning, a hydrogen plasma can be used, but also a hydrogen-nitrogen plasma, a hydrogen-helium plasma, a hydrogen-argon plasma, or any combination of such plasmas. In a further embodiment, the semiconductor technology system includes a controllable faceted mirror arranged in a beam path upstream of the optical element of the optical arrangement. The semiconductor technology system is configured to direct the EUV radiation, at least partially, during the operating break by means of the controllable faceted mirror into an area outside the optical surface, in particular into an area adjacent to the optical surface of the optical element. The area to which the EUV radiation is deflected typically contains the contaminants. The controllable faceted mirror has multiple facets whose orientation can be adjusted independently. Using the controllable faceted mirror, the direction of the EUV radiation striking the respective facets can therefore be selectively changed by setting the faceted mirror to a predefined switching state. In an EUV lithography system, two faceted mirrors are typically arranged one behind the other in the beam path: a field faceted mirror and a pupil faceted mirror. By controlling the field faceted mirror, the intensity distribution on the pupil faceted mirror, which follows in the beam path, can be adjusted. Generally, an intensity distribution is specified on the pupil faceted mirror, depending, among other things, on the structure being imaged on the mask; for example, a so-called dipole or quadrupole intensity distribution.In the proposed embodiment, the field facet mirror can direct the incident EUV radiation to the position or area where the contaminants to be removed are located, this area typically being outside the optical surface of the optical element. Therefore, it is also advantageous in this case to protect the optical element of the optical arrangement from the contaminants released during cleaning by means of a shield spaced away from the optical surface. In this case, the shield is typically positioned in the beam path in front of the optical element of the optical arrangement. Alternatively, the optical element may not have a shield spaced away from the optical surface. In this case, the protection of the optical surface can be achieved in another way. A semiconductor technology system, in particular an EUV lithography system, may comprise: a radiation source for generating EUV radiation, and an optical arrangement configured according to the preamble of claim 1, i.e., comprising an optical element for reflecting EUV radiation, and a cleaning device for providing a cleaning gas to remove contaminants present in the region of the optical element. The semiconductor technology system includes a controllable faceted mirror arranged in a beam path upstream of the optical element of the optical arrangement.The semiconductor technology system is designed to direct the EUV radiation during the operating break, at least partially, into an area outside the optical surface, in particular into an area next to the optical surface of the optical element, by means of the controllable faceted mirror. The semiconductor technology system preferably includes a deposition device configured to deposit a protective layer, particularly in the form of a carbon layer, onto the optical surface of the optical element of the optical arrangement. The protective layer is temporarily deposited on the optical surface before cleaning begins and is removed from the optical surface after or during cleaning. For this purpose, the semiconductor technology system can, for example, include a deposition device configured as in DE 10 2008 028 868 A1 cited above, which is incorporated in its entirety by reference into this application. The deposition device can effect the deposition of the protective layer in different ways: The deposition device can be configured to increase the partial pressure of hydrocarbons near the optical surface in order to deposit the protective layer. For this purpose, the deposition device can have one or more supply lines for introducing the hydrocarbons. Alternatively or additionally, the deposition device can be configured to introduce hydrocarbons into the area of ​​the optical element via one or more supply lines intended for the introduction of hydrogen.The deposition device can alternatively or additionally be configured to lower the hydrogen partial pressure in the region of the optical surface in order to reduce the hydrogen purification rate, thereby depositing a carbon protective layer on the optical surface. Instead of a carbon-containing protective layer, another type of passivation layer can also be used, for example, a phosphorus-containing passivation layer as disclosed in US 20240302756 A1, which is incorporated by reference in its entirety into this application. It is also possible for the deposition device to selectively illuminate the optical surface with a radiation source, such as the EUV radiation source of the semiconductor technology system, precisely where the protective layer is to be deposited, resulting in the "writing" of a carbon protective layer. This method exploits the fact that carbon is deposited particularly in areas with high radiation intensity. During the "writing" of the carbon protective layer, the local thickness of the layer can be adjusted depending on the expected rate of carbon removal during subsequent cleaning, which may be inhomogeneous, especially when contaminants in the area of ​​the pupil facet mirror need to be removed.For "writing" the carbon protective layer, the controllable faceted mirror described above can be used, which directs the EUV radiation precisely to different positions on the optical surface. In particular, the dwell time at each position can be varied to create the desired thickness distribution of the protective layer on the optical surface. It goes without saying that such a procedure is also possible with a protective layer made of a material other than carbon. If the time required to remove the contaminants exceeds the known time required for the complete removal of the protective layer, the cleaning process can be interrupted to reapply the protective layer. It is understood that any remaining carbon protective layer can also be removed from the optical surface after the contaminants have been removed, for example, by increasing the hydrogen partial pressure in the area of ​​the optical surface. A further aspect of the invention relates to a method of the type mentioned at the outset, in which an optical surface of the optical element is protected from the contaminants removed by the cleaning device by at least one shield spaced apart from the optical surface. The shield can be designed or arranged in the manner described above in connection with the optical arrangement. In one variant, the provision of the cleaning gas involves directing a cleaning gas stream to a position outside the optical surface of the optical element, specifically to a position adjacent to the optical surface. As described above, the removal of contaminants occurs in an area outside the optical surface, which is protected from the volatile contaminants generated during cleaning by means of shielding. The cleaning gas stream can be directed to a position with a high concentration of contaminants and / or to a position where a getter surface is located, to which the contaminants are bound. In another variant, at least one shield and preferably at least one cleaning head for supplying the cleaning gas flow are attached to the optical element before the contamination is removed and removed after the contamination has been removed. The shield, which is positioned at a distance from the optical element, can be attached to a holder or detachably fastened in the semiconductor equipment before the cleaning or contamination removal process begins. The same applies to the cleaning head(s). After the cleaning, which typically takes place during a downtime, the shield or cleaning head can be removed from the semiconductor equipment. In another embodiment, the optical element is arranged in an enclosure that encapsulates a beam path of a semiconductor technology system. The enclosure has an opening, to which, in particular, a maintenance shaft is connected. In this embodiment, the shielding, and preferably the cleaning head, is attached through the opening in the area of ​​the optical element and removed after the contaminants have been removed from the area of ​​the optical element. The at least one shielding element can be brought into the area of ​​the optical element through the opening in the enclosure or attached there. The shielding element can be attached to a holder or mounting in the area of ​​the optical element. However, it is also possible for the holder for the shielding element to be arranged in or fixed in the maintenance shaft in order to hold the shielding element in a position spaced away from the optical surface. Particularly if the semiconductor technology system lacks cleaning heads to provide a cleaning gas stream, one or more cleaning heads can be inserted into the interior of the enclosure through the opening. It is understood that the cleaning head(s) should preferably be positioned close to, and / or directed towards, areas with a high concentration of contamination. In another variant, a controllable faceted mirror is arranged in a beam path upstream of the optical element. EUV radiation striking the faceted mirror is, during the removal of contaminants, at least partially directed into an area outside the optical surface of the optical element, specifically into an area adjacent to the optical surface where the contaminants to be removed are typically located. In this case, the EUV radiation is used to activate the cleaning gas provided by the cleaning device, which may be, for example, molecular hydrogen, or to generate a local hydrogen plasma.In this case, activation and cleaning are essentially localized to the area of ​​the contaminants to be removed, which may be located particularly adjacent to the optical surface, for example, on a supporting structure or similar component. The removal of the contaminants takes place during a downtime of the semiconductor technology system in which the optical element and the controllable faceted mirror are located. With this type of contaminant removal, it is possible to forgo the use of shielding (and, if applicable, a protective layer). It is also possible that in the aforementioned method for removing contaminants, where the removal is carried out by supplying a cleaning gas via a cleaning device, a protective layer is deposited on the optical surface to protect it before the contamination is removed. This protective layer could, for example, be a carbon layer. The protective layer, particularly the carbon layer, is typically removed after or during the removal of the contamination; that is, it is a temporarily deposited protective layer. The protective layer can be deposited, for example, using the deposition device described above. The deposition of the protective layer is particularly advantageous when, as described above, a controllable faceted mirror is arranged in a beam path upstream of the optical element, and EUV radiation striking the faceted mirror during the removal of contaminants is directed to an area outside the optical surface, specifically to an area adjacent to the optical surface of the optical element. In this case, the faceted mirror can be controlled to direct the EUV radiation onto the optical surface or to a specific sub-area of ​​the optical surface where the protective layer is to be deposited. By adjusting the parameters of the EUV radiation, such as its intensity, and / or the dwell time in a specific sub-area, a protective layer with a locally varying thickness can be produced.The locally varying thickness of the protective layer can be adapted, in particular, to the expected, and potentially locally varying, removal of the protective layer during the removal of contaminants. Ideally, the protective layer can be completely removed in this way during the removal of the contaminants. However, it is understood that the protective layer, or parts of it, can also be removed even after the removal of the contaminants. If the removal of contaminants takes longer than the time required to completely remove the protective layer from the entire optical surface or from one or more localized areas, the faceted mirror can be controlled to direct the EUV radiation onto the optical surface and re-deposit the protective layer, at least in the removed areas. The optical element used to remove the contaminants can be an optical element directly following the controllable faceted mirror in the beam path, such as another faceted mirror, or it can be an optical element not directly following the faceted mirror in the beam path. Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures in the drawing, which show details essential to the invention, and from the claims. The individual features can be implemented individually or in any combination in a variant of the invention. drawing Exemplary embodiments are shown in the schematic drawing and explained in the following description. Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography with an optical arrangement comprising a field facet mirror. Figs. 2a and 2b show schematic representations of an optical arrangement with the field facet mirror, a cleaning head, and a shield arranged next to an optical surface to protect the optical surface from contamination. Figs. 3a and 3b show schematic representations analogous to Figs. 2a and 2b, in which the shield is arranged in front of the optical surface, forming a gap. In the following description of the drawings, identical reference symbols are used for identical or functionally equivalent components. Fig. 1 shows a simplified representation of an EUV projection exposure system 100 for microlithography, which is hereinafter also referred to as an EUV lithography system. The EUV lithography system 100 has a housing 101 enclosing an interior space and at least one, in this case several, optical elements 102 to 112 arranged in the housing 101. In the example shown, the EUV lithography system 100 further comprises a radiation source 113 in the form of an EUV light source, an illumination system 114 for illuminating an object field 115 in an object plane 116, and a projection system 117. The illumination system 114 illuminates a reticle 118 arranged or arrangable in the object field 115, which is held by a reticle holder 119. The projection system 117 serves to map the object field 115 into an image field 120 in an image plane 121.A structure of the reticulum 118 is imaged onto a photosensitive layer of a wafer 122 located in the image plane 121 within the image field 120 and held by a wafer holder 123. The wafer 122 is made of a semiconductor material, for example silicon. The radiation source 113 emits EUV radiation 124, particularly in the range between 5 nm and 30 nm, and especially at 13.5 nm. To control the radiation path of the EUV radiation 124, preferably at least one of the optical elements 102 to 112, and in particular each of the optical elements 102 to 112, is controllable, especially for respective alignment or positioning. The EUV radiation 124 generated by the radiation source 113 is aligned by means of a collector mirror integrated in the radiation source 113 (not shown) such that the EUV radiation 124 passes through an intermediate focus 125 in the region of an intermediate focus plane before the EUV radiation 124 subsequently strikes a first of the optical elements 102, in this case a field facet mirror 102. After the field facet mirror 102, the EUV radiation 124 is directed onto a second of the optical elements, in this case a pupil facet mirror 103.The light is then guided through the further optical elements 104, 105, 106 to the object field 115. The reticle 118 arranged or arrangable in the object field 115 is, for example, a reflective photomask having reflective and non-reflective, or at least less reflective, areas for generating at least one structure to be imaged. Alternatively, the reticle 118 is formed by a plurality of micromirrors arranged in a one- or multi-dimensional configuration and preferably movable about at least one axis. The reticule 118 reflects part of the EUV radiation 124 coming from the lighting system 114 into the projection system 117 and shapes the light reflected into the projection system 117 in such a way that the information about the structure of the reticule 118 is transferred to the image plane 120 by means of the projection system 117. In the present example, the projection lens 17, without being limited to this number, has six optical elements 107 to 112. The EUV projection exposure system 100 further comprises sub-housings 126, 127, 128 arranged in the housing 101, each of which at least partially encloses one of the optical elements 102, 103, 104. The sub-housings 126, 127, 128 serve to prevent or at least reduce contamination, in particular particle contamination, of the area at least partially enclosed by the sub-housings 126, 127, 128, and especially contamination of the optical elements 102, 103, 104 and the reticle 118. The sub-housings 126, 127, 128 are at least partially connected to each other, so that the sub-housings 126, 127, 128 encapsulate the beam path of the EUV radiation 124 formed by the optical elements 102, 103, 104 within the illumination system 114, i.e. each sub-housing 126, 127, 128 forms an enclosure for encapsulating the beam path. Despite the arrangement of the optical elements 102, 103, 104 in the sub-housings 126, 127, 128, contamination with particles cannot be completely ruled out, especially if the particles are distributed along the beam path of the EUV radiation 124. For example, the contaminants could be tin particles that originate within the radiation source 113 for generating the EUV radiation 124 and spread along the beam path of the EUV radiation 124. These particles, located within the sub-housings 126, 127, 128, could, for example, settle on the inner walls of the sub-housings 126, 127, 128 or on and / or next to the optical elements 102, 103, 104. It has been shown that areas adjacent to the optical surfaces 102a, 103a, ... of the optical elements 102, 103, ... exhibit a particularly high concentration of contamination, especially in the form of tin particles. The contamination in the form of the deposited particles can be transferred into the gas phase by so-called hydrogen-induced outgassing or by so-called "cold spitting" and reach the reticle 118, which impairs the image quality of the EUV lithography system 100. This is particularly problematic when the EUV lithography system 100 has reached a comparatively long operating time and a large number of contaminants have accumulated in the illumination system 114. To remove the accumulated contaminants 130 in the form of particles in the area of ​​the field facet mirror 102 of the illumination system 114, more precisely to transfer them into the gas phase, an optical arrangement 131 is used, which is shown in Fig. 2a,b. The optical arrangement 131 comprises the field facet mirror 102 and a cleaning device 132, which serves to provide a cleaning gas 133. The cleaning device 132 has a cleaning head 134, which is designed to provide the cleaning gas in the form of a cleaning gas stream 133 (see Fig. 2b). The cleaning head 134, and thus also the cleaning gas stream 133, is directed towards a position P outside the optical surface 102a of the faceted mirror 102, which is located within an area where a particularly high concentration of deposited contaminants 130 is present. In the example shown, position P is located adjacent to the optical surface 102a, specifically on a non-optical surface 135a of a support component of the faceted mirror 102 (not shown in Fig. 2a,b). In the example shown, the cleaning gas stream 133 forms a hydrogen plasma, i.e., it contains mostly ionic hydrogen species and only a small proportion of activated, neutral hydrogen species. The hydrogen plasma enables, in particular, the transfer of contaminants 130 in the form of tin particles into the gas phase, where they react with the hydrogen to form volatile stannanes. The optical arrangement 131, more precisely the cleaning device 132, has a shield 136 to protect the optical surface 102a of the faceted mirror 102 from contaminants 130 that are removed from the surface 135a of the support component 135 during cleaning and transferred into the gas phase. The shield 136 is arranged at a distance from the optical surface 102a of the field faceted mirror 102. In the example shown, the shield 136 is a housing that surrounds an interior space 137 shown in Fig. 2b, in which position P is located, towards which the cleaning head 134, more precisely a nozzle of the cleaning head 134, is directed. The shield 136 is arranged next to the optical surface 102a at a distance from it. A side wall of the shield 136 facing the optical surface 102a is positioned between the cleaning head 134 and the optical surface 102a. This prevents contaminants 130, detached by the cleaning gas stream 133 and carried into the gas phase, from reaching and contaminating the optical surface 102a. In the example shown, the shield 136 is open only towards the surface 135a of the support component that is to be cleaned by the cleaning gas stream 133. The shield 136, or more precisely its underside, can generally be in contact with the surface 135a to be cleaned, but it is also possible for a narrow gap to remain between the shield 136 and the surface 135a. It is also possible for the shield 136 to be partially, e.g.,at one edge of its side wall facing the optical surface 102a, it rests against the surface 135a and the other edges are spaced away from the surface 135a to be cleaned on the underside of the shield 136. In the example shown, the shield 136 has an extraction port 138, which serves to extract the contaminants 130 and the cleaning gas 133 removed by the cleaning device 132 from the interior 137. An inner surface 136a of the shield 136 serves as a getter surface and is fully coated with a coating of a getter material. The getter material of the coating can, for example, be selected from the group including: Ru, Ni, NiP, Pt, Rh, Ir, etc. Figures 3a and 3b also show an optical arrangement 131, which differs from the optical arrangement 131 of Figures 2a and 2b essentially in the type and arrangement of the shielding 136'. In Figures 3a and 3b, the shielding 136' is plate-shaped and has a circular geometry adapted to the shape of the optical surface 102a. The shielding 136' is made of a metallic material and completely covers the optical surface 102a in the example shown. Between the shield 136' and the optical surface 102a there is a gap 140, which in the example shown has a maximum width b of less than 1 cm. The distance between the shield 136' and the optical surface 102a is constant in the example shown, but this is not strictly necessary. As can be seen in the sectional view shown in Fig. 3b, the optical surface 102a of the faceted mirror 102 is divided into two halves, separated by an essentially horizontal obscuration 139. As in Figs. 2a and 3b, the contaminants 130 are also deposited adjacent to the optical surface 102a in Figs. 3a and 3b and are removed from the surface 135a of the support component 135 by means of a cleaning device 132, more precisely by means of a cleaning gas stream 133. The optical arrangement 131 also includes a purge device 141 for supplying a purge gas stream 142 into the space 140 between the shield 136' and the surface 102a. The purge gas of the purge gas stream 142 can be, for example, molecular hydrogen or an inert gas. In the example shown, the purge gas stream 142 is directed towards position P, where the contaminants 130 have accumulated, in order to prevent the ingress of the contaminants 130, which are converted into the gaseous state during cleaning. The shield 136' prevents the contaminants 130, which are detached during cleaning, from adhering to the optical surface 102a. However, the purge device 141 can also – in a preferred embodiment – ​​be positioned in the central region, particularly in the center of the shield 136'. In an alternative embodiment, indicated by dashed lines in Fig. 3b, the shielding 136' is arranged only in an outer, annular region 136a' at a small distance b from the optical surface 102a. The annular region 136a' projects laterally beyond the optical surface 102a and has a radial length L of more than 1 cm, e.g., 2 cm or more. The width b of the space 140 between the annular region 136a' and the optical surface 102a is less than 1 mm, for example, 0.5 mm, 0.3 mm, or less. In a radially inner area 136b' adjoining the annular area 136a', which is indicated by a dashed line, the shielding 136' extends away from the optical surface 102a in this embodiment and has a greater distance from the optical surface 102a in order to avoid contact with the optical surface 102a during assembly.The shielding 136' can in this case be designed, for example, in the form of a pot or the like. The contaminants 130 transferred into the gas phase during cleaning can be pumped out of the EUV lithography system 101 in the optical arrangement 131 of Fig. 3a,b and / or captured or bound by getter surfaces. In the example shown, the inner surfaces 126a, 127a, 128a of the partial housings 126, 127, 128, each forming an enclosure, are at least partially designed as getter surfaces and coated with a getter material; however, they can also be designed as getter surfaces over their entire surface. In the optical arrangements 131 shown in Figs. 2a,b and 3a,b, the removal of contaminants takes place during an operational break when the radiation source 113 typically does not generate EUV radiation 124. For cleaning, in Figs. 2a,b and 3a,b, the shielding 136, 136' is attached in the area of ​​the faceted mirror 102 during the operational break before the removal of the contaminants 130 begins. In the example described in Figs. 2a,b, the entire cleaning device 132 is arranged in the area of ​​the faceted mirror 102, while in the example described in Figs. 3a,b, only the shielding 136' is attached in the area of ​​the faceted mirror 102, since the cleaning head 134 is permanently installed in the EUV lithography system 100. The shield 136' can be held above the optical surfaces 102a by means of a holder (not shown). After the removal of the contaminants 130, the cleaning device 132 is used.The shielding 136' was removed again from the area of ​​the faceted mirror 102 and from the EUV lithography system 100 in order to resume exposure operation. As can be seen in Fig. 1, the housing 126, 127, 128 for encapsulating the beam path has an opening 144, to which a maintenance shaft 145 is connected. In the example described in Fig. 2a, b, the cleaning device 132 is installed via the maintenance shaft 145 and the opening 144 in the area of ​​the faceted mirror 102. In the example shown in Fig. 3a, b, only the shielding 136' is installed in the area of ​​the faceted mirror 102. For this purpose, a bracket for the cleaning device 132 or for the shielding 136' can be arranged and fixed in the maintenance shaft 145. Alternatively, it is possible to fix the cleaning device 132 or the shielding 136' to a suitable bracket located inside the housing 126, 127, 128. It is also possible that a shield 136', designed as in Fig. 3a,b, is arranged at a distance from an optical element during cleaning, and that no cleaning gas stream 133 is used for the cleaning process. Fig. 1 shows an example of such cleaning, which is carried out on an optical element in the form of the pupil facet mirror 103, which follows the field facet mirror 102 in the beam path. In this case, the radiation source 113 is activated during the operational break when the contaminants 130 are removed. The field facet mirror 102, arranged in the beam path in front of the pupil facet mirror 103, is controlled by a control device (not shown) for the removal of the contaminants 130 in order to deflect the EUV radiation 124 reflected at the field facet mirror 102 into an area 146 adjacent to the pupil facet mirror 103 where the contaminants 130 are located, as shown in Fig.1 is indicated by a dotted beam path. In this case, the cleaning device 132 does not have a cleaning head 134, but instead supplies the cleaning gas 133 in the form of molecular hydrogen via a feed line (not shown) located in the EUV lithography system 100. The cleaning gas 133, in the form of molecular hydrogen, is activated by the deflected EUV radiation 134, and a local hydrogen plasma is formed. This plasma removes the contaminants 130 in the area 146, on which the deflected EUV radiation 134 is directed. As shown in Fig. 3a,b, the shield 136' protects the optical surface 103a from the contaminants 130 that have been transferred into the gas phase. However, it is also possible to omit the shield 136' or, if necessary, any protection of the optical surface 103a entirely with this type of cleaning. As an alternative to using the shielding 136', the optical surface 103a of the pupil facet mirror 103 can be protected from contamination 130 during this type of cleaning, or generally, by applying a protective layer 147 to the surface 103a, which in the example shown is a carbon layer. The carbon protective layer 147 can be produced in various ways. In the example shown, the protective layer 147 is produced by introducing gaseous hydrocarbons into the area of ​​the pupil facet mirror 103, or in the vicinity of its optical surface 103a, by means of a gas supply 148. The hydrocarbons are irradiated with EUV radiation 124 to form the protective layer 147.By controlling the field facet mirror 102, it is possible in principle to expose any position of the optical surface 103a of the pupil facet mirror 103 to the EUV radiation 124 and to virtually “write” the protective layer 147. In this way, the protective layer 147 on the optical surface 103a can be created with a locally variable thickness. The local thickness of the protective layer 147 can be adjusted, in particular, such that the protective layer 147 is completely removed during the removal of the contaminants 130, when cleaning gas 133 also reaches the protective layer 147. Alternatively, it is possible to remove any remaining protective layer 147 from the optical surface 103a after the removal of the contaminants 130 is complete. In principle, with the cleaning process described here, which does not require a cleaning head, it may also be possible to dispense with a shield 136' or a protective layer 147 on the optical surface 103a. It is understood that not only tin particles but also other types of contaminants 130 can be removed in the manner described above, in particular contaminants or particles that are susceptible to chemical reactions with hydrogen, e.g. Si, Pb, Zn, P, F, etc. The removal of the contaminants 130 or the cleaning can also be carried out on other optical elements of the EUV lithography system 100 besides the field facet mirror 102 or the pupil facet mirror 103. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 10 2008 028 868 A1 [0011, 0043]DE 10 2009 012 091 A1

[0012] EP 4318133 A1

[0013] DE 10 2011 079 450 A1

[0014] US 8,419,862 B2 [0015, 0023]DE 10 2015 219 939 A1

[0016] DE 10 2009 045 170 A1

[0016] DE 10 2016 204 904 A1

[0016] DE 10 2022 212 168 A1

[0016] DE 10 2009 001 488 A1

[0017] DE 10 2017 213 176 A1

[0017] US 20240302756 A1

[0043] Cited non-patent literature D. Shefer, Eindhoven University of Technology, 2023

[0008] https: / / wernerwirth.com / komponentenschutz / verarbeitungstechnik / plasmatechn ologie /

[0036]

Claims

Optical arrangement (131) comprising: an optical element (102, 103) for reflecting EUV radiation (124), and a cleaning device (132) for providing a cleaning gas (133) for removing contaminants (130) present in the area of ​​the optical element (102, 103), characterized in that the optical arrangement (131) has at least one shield (136, 136') spaced apart from the optical surface (102a, 103a) to protect an optical surface (102a, 103a) of the optical element (102, 103) from the contaminants (130) removed by means of the cleaning device (132). Optical arrangement according to claim 1, wherein the cleaning device (132) has at least one cleaning head (134) for providing the cleaning gas in the form of a cleaning gas stream (133), wherein the cleaning head (134) is aligned or alignable to a position (P) outside the optical surface (102a) of the optical element (102), in particular to a position (P) adjacent to the optical surface (102a) of the optical element (102). Optical arrangement according to claim 2, wherein the shielding (136) is arranged at least partially between the cleaning head (134) and the optical surface (102a), wherein the shielding (136) preferably surrounds an interior (137) in which the cleaning head (134) provides the cleaning gas stream (133). Optical arrangement according to claim 3, wherein the shield (134) has a suction (138) for suctioning the contaminants (130) removed by means of the cleaning device (132) and the cleaning gas (133) from the interior (137). Optical arrangement according to one of the preceding claims, wherein the shielding (136') at least partially, in particular completely, covers the optical surface (102a), wherein a gap (140) is formed at least sectionally between the shielding (136') and the optical surface (102a), which preferably has a maximum width (b) of 1 cm or less, particularly preferably of 0.5 cm or less. Optical arrangement according to claim 5, further comprising: a rinsing device (141) for supplying a rinsing gas stream (142) into the space (140) between the shield (136') and the surface (102a). Optical arrangement according to one of the preceding claims, further comprising: at least one getter surface (136a, 126a, 127a, 128a) for binding the contaminants (130) removed by means of the cleaning device (132), wherein the getter surface (126a, 127a, 128a) is preferably formed on an inside of an enclosure (126, 127, 128) which encapsulates a beam path of the optical arrangement (131), and / or on an inside (136a) of the shield (136) which surrounds the interior (137). Semiconductor technology system, in particular EUV lithography system (1), comprising: a radiation source (113) for generating EUV radiation (124), and at least one optical arrangement (131) according to one of the preceding claims. Semiconductor technology system according to claim 8, which is designed to remove the contaminations (130) during an operating break, wherein the radiation source (113) is preferably activated during the operating break. Semiconductor technology system according to claim 9, which has a controllable faceted mirror (102) which is arranged in the beam path in front of the optical element (103) of the optical arrangement (131), wherein the semiconductor technology system (100) is configured to direct the EUV radiation (124) at least partially into an area (146) outside the optical surface (103a) during the operating break by means of the controllable faceted mirror (102), in particular into an area (146) next to the optical surface (103a) of the optical element (103). Method for removing contaminants (130) present in the area of ​​an optical element (102, 103) for the reflection of EUV radiation (124), comprising: removing the contaminants (130) by providing a cleaning gas (133) by means of a cleaning device (132), characterized in that an optical surface (102a, 103a) of the optical element (102, 103) is protected from the contaminants (130) removed by means of the cleaning device (132) by at least one shield (136, 136') spaced apart from the optical surface (102a, 103a). The method of claim 9, wherein the provision of the cleaning gas comprises directing a cleaning gas stream (133) to a position (P) outside the optical surface (102a, 103a) of the optical element (102, 103), in particular to a position (P) next to the optical surface (102a, 103a) of the optical element (102, 103). Method according to claim 9 or 10, wherein the at least one shield (136, 136') and preferably at least one cleaning head (134) for providing the cleaning gas flow (133) are attached before the removal of the contaminants (130) in the area of ​​the optical element (102, 103) and are removed after the removal of the contaminants (130) from the area of ​​the optical element (102, 103). Method according to claim 13, wherein the optical element (102, 103) is arranged in an enclosure (126, 127, 128) which encapsulates a beam path of a semiconductor technology system (100), wherein the enclosure (126, 127, 128) has an opening (144) to which, in particular, a maintenance shaft (145) is connected, and wherein the shielding (136, 136') and preferably the cleaning head (134) are attached via the opening (144) in the area of ​​the optical element (102, 103) and are removed after the removal of the contaminants (130) from the area of ​​the optical element (102, 103). Method according to one of claims 11 to 14, in which a controllable faceted mirror (102) is arranged in the beam path in front of the optical element (103) and EUV radiation (124) incident on the controllable faceted mirror (102) is directed at least partially into an area (146) outside the optical surface (103a) when removing the contaminants (130) by means of the controllable faceted mirror (102), in particular into an area (146) next to the optical surface (103a) of the optical element (103).

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