Optical assembly with porous particle capture structure and semiconductor system

Abstract

The invention relates to an optical assembly (4) for a semiconductor lithography system, in particular for a projection exposure system, comprising: at least one housing (32, 32') having an interior (33, 33'), and at least one optical component (19, 20, 21), which has a surface (19a, 20a, 21a) facing the interior (33, 33'). The optical assembly (3) has at least one porous particle capture structure (29, 29'), which is arranged on an inner face (34a, 34a') of a wall (34, 34') of the housing (32, 32') or is accommodated in the wall of the housing, for capturing contaminating particles (24a, 24b) present in the interior (33, 33'). The invention also relates to a semiconductor lithography system, in particular a projection exposure system, which has at least one such optical assembly (4).

Description

[0001] Optical assembly with porous particle trapping structure and semiconductor technology system

[0002] Reference to related registration

[0003] This application claims priority over German patent application DE102024207260.5 dated July 31, 2024, the entire disclosure content of which is incorporated by reference into this application.

[0004] Background of the invention

[0005] The invention relates to an optical assembly for a semiconductor technology system, in particular for a projection exposure system, comprising: at least one housing with an interior space, and at least one optical component with a surface facing the interior space. The invention also relates to a semiconductor technology system comprising at least one such optical assembly.

[0006] Contamination occurring in semiconductor technology equipment, particularly in projection exposure systems, can lead to a reduction in the optical performance and transmission of the system, and thus in the throughput, i.e., the number of wafers per hour. This problem is especially prevalent with tin contamination, which in projection exposure systems for EUV lithography can occur in the form of liquid particles, solid particles, and gaseous molecular components, e.g., SnH₂. x, and which lead to a loss of reflectivity in the optical components present, such as mirror elements. In an EUV projection exposure system, the tin contamination is typically generated by an LPP (laser-produced plasma) radiation source and can penetrate the illumination system of the EUV projection exposure system via an intermediate focus. The majority of the tin contamination strikes the mirror elements and contaminates them. A smaller portion can strike mechanical components at grazing incidence, be reflected there, and may reach the mask. To capture the contamination in the form of tin particles and prevent their deposition on the surfaces of optical components, shielding is used that mechanically blocks the tin particles. For example, this can prevent the ingress of contamination into the interior of a housing or...The tin particles are prevented from entering an environment where optical components are located. However, they may still rebound off the shielding and, despite the shielding, reach the vicinity of the optical components and contaminate them.

[0007] DE102005017265A1 describes a device for cleaning a gas mixture containing particles. The device is designed as a filter, in particular as a diesel particulate filter, which has a porous surface exposed to the gas mixture made of a filter base material, onto which a layer of ceramic fibers is applied, which may contain aluminum dioxide, an aluminosilicate and / or zirconium dioxide.

[0008] EP 1743221 B1 proposes removing particles generated by a radiation source using a first gas that is guided transversely to the direction of radiation propagation between the radiation source and a particle trap located in the wall of a mirror chamber. A second gas is introduced into the mirror chamber, its pressure being adjusted to be at least as high as that of the first gas to prevent the first gas from entering the mirror chamber. EP 2465012 B1 describes a lithography system comprising a chamber with at least one optical component for reflecting radiation, wherein a membrane defines a portion of the chamber and is configured to prevent the passage of contaminant particles through the membrane.The lithography system also includes a particle trapping structure configured to allow gas to flow along an indirect path from inside to outside the chamber. This indirect path is configured to prevent the passage of contaminant particles from inside to outside the chamber. The particle trapping structure may be made of a sponge-like material that is impermeable to contaminant particles while allowing gas to flow through it. This porous, sponge-like material may be constructed from a metal that is non-reactive to the atmosphere in which the particle trapping structure is used. In the case of a hydrogen-containing atmosphere, suitable non-reactive metals include aluminum, tungsten, ruthenium, and molybdenum.

[0009] Object of the invention

[0010] The object of the invention is to provide an optical assembly and a semiconductor technology system in which the number of contaminating particles present in the interior that can reach the surface of the optical component is reduced.

[0011] Subject matter of the invention

[0012] This problem is solved by an optical assembly of the type mentioned above, which has at least one porous particle trapping structure arranged on an inner side of a housing wall or embedded in the housing wall for trapping contaminating particles present in the interior. The porous particle trapping structure is typically located outside the beam path of the semiconductor technology arrangement into which the optical assembly is integrated. For the purposes of this application, the term "particles" includes solid, liquid, or gaseous particles, as well as particles in the form of gaseous, in particular hydrogen-volatile, compounds, e.g., in the form of SnH₂. x , understood.

[0013] According to the invention, a porous particle trapping structure is used to capture contaminating particles, particularly tin particles. This structure is arranged on or formed on a wall of the housing, or is incorporated into or integrated into the wall of the housing. Unlike a shield, where particles are arranged on or formed on a wall of the housing, the porous particle trapping structure, which is generally designed in the form of a sponge, does not reflect incident particles by an elastic collision. Instead, they penetrate the porous particle trapping structure, gradually transferring their energy to it and being decelerated until they come to a standstill. This principle was used, for example, in NASA's Stardust Detector to capture dust from meteorites. In contrast to the description in EP2465012B1, the porous particle trapping structure on or formed on the wall of the housing serves a different purpose.in the wall of the housing not to allow a gas to flow along an indirect path from inside the chamber to outside the chamber.

[0014] The housing can completely or partially enclose the optical component(s). In particular, the housing can be the housing of a lighting system or a projection system of a projection exposure unit. In this case, the optical component is located inside the housing. It is also possible that the housing is an enclosure or a housing located within another housing to encapsulate the beam path of the semiconductor technology system, as described, for example, in DE102021210101A1, which is incorporated in its entirety by reference into this application. In this case, the optical component may be located adjacent to or adjacent to the enclosure or form part of the enclosure. Again, in this case, a surface of the optical component, which may be, for example, a mirror, faces the interior of the housing in the form of the enclosure.

[0015] In one embodiment, the porous particle trapping structure is attached to a gas-tight component, preferably to the wall of the housing, the housing being designed, in particular, to encapsulate a beam path. In the simplest case, the gas-tight component can be the wall of the housing to which the porous particle trapping structure is arranged or attached; however, it is also possible for the gas-tight component to form a substrate onto which the porous particle trapping structure is applied. In this case, the porous particle trapping structure, together with the substrate, forms a single unit that is attached to the inside of the housing wall. In the embodiment described here, the porous particle trapping structure cannot be completely permeated by a gas, since the porous particle trapping structure is attached to the gas-tight component at its rear side, which faces away from the interior.

[0016] The housing can be configured, in particular, to encapsulate a beam path of the semiconductor technology system, especially the projection exposure system. In this case, the wall of the housing is located a short distance from the edge of the beam path, and the housing, or rather its wall, essentially follows the geometry of the beam path. The housing encapsulating the beam path is typically located within a further, outer housing. The arrangement of the porous particle trapping structure on an inner wall of a housing encapsulating the beam path is advantageous because certain contaminating particles, such as tin particles, are more prevalent in the interior of such a housing.

[0017] In another embodiment, the porous particle trapping structure is detachably connected to the inside of the housing wall. In this case, the particle trapping structure(s) can, for example, be designed as tiles or similar materials lining the inside of the housing wall. Alternatively, the particle trapping structure(s) can be fixed inside the housing using a device, allowing for free positioning. This interchangeability makes it possible to replace the porous particle trapping structure and, if necessary, reprocess it by removing the trapped particles.

[0018] In another embodiment, the porous particle trapping structure is formed from an aerogel. Aerogels are highly porous materials with a solids content typically of 2 vol% or less. Aerogels were used, for example, in NASA's Stardust Detector described above to capture dust from meteorites. This involved an array of 30 mm thick SiO₂ aerogel blocks, which had a volume density of 2% of SiO₂ and a pore size of a few nanometers. The largest captured particles were 100 pm in size. The density of the aerogel was chosen to be so low that the impacting particles remained unchanged and could be analyzed in their original form and composition. The longest stopping distances were 200 times the particle size, which is why a thickness of slightly more than 20 mm for the aerogel blocks was sufficient for this purpose.

[0019] In a further embodiment of this design, the aerogel is configured as a metal oxide aerogel or as a metallic aerogel, wherein the metal oxide of the metal oxide aerogel is preferably selected from the group comprising: aluminum oxide, chromium oxide, titanium oxide, zirconium oxide, tungsten oxide, molybdenum oxide, hafnium oxide, and iron oxide. For an overview of metal oxide aerogels, reference is made to the article “Metal oxide aerogels for high-temperature applications”, Wu, Y., Wang, X. & Shen, J., J Sol-Gel Sei Technol 106, 360-380 (2023), which is incorporated in its entirety by reference into this application. The aerogel should be formed from a material resistant to the atmosphere in the interior of the housing. In the event that hydrogen is present in the interior, the SiO2 aerogel described above, for example, cannot be used. A metallic aerogel, such as an aluminum aerogel, can also be used as a particle trapping structure.

[0020] In a further development, the aerogel is designed as a gas-binding aerogel, preferably as a ruthenium aerogel, a nickel aerogel, or a NiP aerogel. Gas-binding materials enable the chemical binding of contaminating substances or particles. For details on gas-binding materials, especially those used to bind hydrogen-induced outgassing (HIO) substances or compounds, please refer to DE102021210101A1 described above.

[0021] Aerogels, as gas-binding materials, offer the advantage of having a very large specific surface area, which, for example, in the case of carbon aerogels is 3000 m². 2 can exceed / g, see below.

[0022] “https: / / faszinationchemie.de / makromolekulare-chemie / news / aerogele-polymere-mit-besonderen-eigenschaften / ”. Aerogels therefore offer an enormous surface area for the adhesion of contaminants. Alternatively or additionally to the arrangement of gas-binding aerogels on the inside of a housing wall or within the housing wall, they can also be attached to components located inside the housing or designed as components within the housing, for example, on shields, e.g., in the form of shielding plates, to increase the service life of optical components, especially mirrors.

[0023] Nickel, ruthenium, or NiP, for example, can be used as gas-binding materials, particularly for hydrogen-volatile particles or compounds. The production of a NiP / SiCh aerogel is described, for instance, in the article "Amorphous NiP / SiCh aerogel: Its preparation, its high thermal stability and its activity during the selective hydrogenation of cyclopentadiene to cyclopentene," Wei-Jiang Wang et al., Applied Catalysis A: General, Vol. 166, Issue 2, L243-L247, 1998. A purely metallic nickel aerogel can also be used for this purpose; see, for example, the article "A Highly Compressible, Elastic, and Air-Dryable Metallic Aerogels via Magnetic Field-Assisted Synthesis," W. Pan et al., Advanced Functional Materials, Vol. 32, Issue 43, 2022.

[0024] In an alternative embodiment, the porous particle trapping structure is formed from a metal foam, in particular an open-cell metal foam. In this embodiment, the entire structure, i.e., the entire porous particle trapping structure, can be formed as a macroscopic metal foam, meaning that it does not need to be applied to a support substrate. Metal foams can also trap particles by slowing them down; however, the pores of metal foams have a comparatively small minimum diameter on the order of approximately 300–500 pm (see, for example, the link).

[0025] "https: / / www.ifam.fraunhofer.de / content / dam / ifam / de / documents / dd / lnfoblätter / o ffenzellige_metallische_schaeume_fraunhofer_ifam_dresden.pdf." The porosity of open-cell metal foams is on the order of approximately 75% to 96%, and the relative density can range from approximately 5% to approximately 30%. Open-cell metal foams are used, among other things, as substrates for catalysts. In a further development of this embodiment, the metal foam is formed from and / or coated with a gas-binding material, preferably selected from the group comprising: Ru, Ni, Rh, Pd, Pt. Metal foams have the advantage that they can consist of a material that binds volatile hydrogen (HlO) species, e.g., nickel or, optionally, rhodium. In the event that the metal foam material is not gas-binding, the metal foam can easily be treated with a chemically active material, e.g.The metal foam can be coated with nickel or palladium to selectively modify or enhance its gas-binding effect on volatile gaseous particles or species. It is understood that the metal foam can also be composed of and / or coated with multiple gas-binding materials. The coating with the gas-binding material can, for example, have a thickness between approximately 1 nm and 10 pm. Metallic sheets, plates, or similar components used as shielding can also be manufactured from or coated with a gas-binding material.

[0026] In another embodiment, the optical assembly includes a heating device for heating the porous particle trapping structure, in particular the metal foam, to a temperature higher than the melting point of tin. The melting point of tin is approximately 231 °C at normal pressure; in a vacuum environment, such as that found inside the housing, this temperature may deviate slightly (< 10 K). It is advantageous to maintain the porous particle trapping structure at a temperature higher than the melting point of tin, as any tin particles that strike it will then remain liquid or become liquid and can be bound by alloying and subsequent solidification. The heating device can, for example, be designed as a resistance heater.In a further development of this embodiment, the metal foam is formed from a material and / or coated with a material that forms an alloy with tin. When the porous particle trapping structure is heated to a temperature higher than the melting point of tin using the heating device, the porous particle trapping structure preferably comprises metals and / or coatings that readily form near-surface, intermetallic alloys with tin. Materials whose solderability with tin is considered good are preferably used, for example, silver, gold, palladium, rhodium, or nickel.It has been shown that in a vacuum environment, particularly in a semiconductor technology system in the form of a projection exposure system for the EUV wavelength range, where reactive hydrogen species are also present, the basic conditions for alloy formation according to the principle of fluxless vacuum soldering are surprisingly well met, see the link “https: / / bondpulse.com / en / vacuum-soldering”.

[0027] It is additionally or alternatively possible to apply an electrical potential to the porous particle trapping structure in order to attract electrically charged contaminating particles. For this purpose, the optical assembly can include a voltage source that maintains the particle trapping structure at a suitable electrical potential.

[0028] In another embodiment, the porous particle trapping structure has a thickness between 1 mm and 20 mm, preferably between 5 mm and 10 mm. It is sufficient to design the porous particle trapping structure with a thickness sufficient to stop the largest particles just below the surface of the porous particle trapping structure facing the interior, even if they are reflected at the rear of the structure or at the gas-tight component. The thickness of the porous particle trapping structure is typically chosen to be slightly greater than half the stopping distance of the particles with the lowest stopping power. The particle size of the tin particles to be trapped is typically on the order of approximately 0.1 pm to approximately 100 pm. Typical velocities of the tin particles are on the order of approximately 1 m / s to 100 m / s.

[0029] The porous particle trapping structure described above, e.g. in the form of an aerogel or in the form of a particularly open-cell metal foam, can also be produced using a 3D printing process.

[0030] In another embodiment, the porous particle trap structure is embedded in the wall of the housing, and an intake device, particularly a Venturi nozzle, is attached to a side of the porous particle trap structure facing away from the interior, specifically within the wall of the housing, for drawing gas from the interior. In this case, the gas flows through the porous particle trap structure, which then acts as a filter that captures the contaminating particles contained in the gas. If the semiconductor technology arrangement is an EUV projection system, the interior is evacuated, and a residual gas, typically containing hydrogen, remains in the interior.

[0031] In a further development of this embodiment, the intake device is integrated into a supply device for introducing a gas into the interior. The supply device can, for example, supply hydrogen to the interior and be designed as a fluid line, which may be integrated into the wall of the housing, but need not be. Through the intake device, particularly in the form of a Venturi nozzle, a portion of the gas supplied to the interior is drawn in and, after filtration by the porous particle trapping structure, is reintroduced into the interior. In the solution described here, a gas flow is generated in the interior between an outlet opening of the supply device and the porous particle trapping structure or the intake device, which the contaminating particles follow.

[0032] Another aspect of the invention relates to a semiconductor technology system, preferably a projection exposure system, particularly for EUV lithography, comprising: at least one optical assembly configured as described above. The semiconductor technology system may be a projection exposure system for exposing a wafer or another semiconductor technology system, for example, an inspection system, e.g., for inspecting masks, wafers, or the like used in lithography. In the case of a projection exposure system for EUV lithography, it is designed for useful radiation at a working wavelength in the extreme ultraviolet (EUV) wavelength range, i.e., in a range of approximately 5 nm to approximately 30 nm.Since wavelengths in this range are strongly absorbed by almost all materials, transmissive optical elements cannot typically be used. Reflective optical elements are therefore necessary. Such EUV radiation-reflecting optical elements can be, for example, mirrors, reflective monochromators, collimators, or photomasks. Because EUV radiation is also strongly absorbed by air molecules, the EUV radiation path occurs in a vacuum environment. Therefore, a vacuum also prevails inside the housing of the optical assembly during the operation of such a projection exposure system.

[0033] In one embodiment, the semiconductor technology system includes a shield for blocking contaminating particles, which is located outside the system's beam path. The shield serves to mechanically block the contaminating particles and can, for example, prevent them from entering the interior of the housing described above and reaching the optical component(s). Such a shield is typically made of a material resistant to hydrogen-volatile species. This material could be, for example, stainless steel or coated aluminum. The shield should be located outside the beam path to avoid obstructing it. However, the shield can limit the beam path at its edges and, for example, be designed in the form of an aperture.It is also possible to manufacture the shielding from a gas-binding material or to coat it with a gas-binding material. Such a coating can be omitted if the particle trapping structure or corresponding getter surfaces already fulfill the getter functionality.

[0034] In general, it is advantageous to combine all three measures described here to reduce the concentration of contaminating particles, especially tin particles; that is, to carry out mechanical blocking to prevent the penetration of tin particles or tin compounds into the environment of EUV mirrors, the above-described trapping of the particles to immobilize them, and the binding of the particles by a chemical reaction ("gettering") together.

[0035] It is also possible to trap the particles using particle trapping structures, for example, in the form of metallic plates, metal grids, or the like, or to combine such particle trapping structures with the porous particle trapping structures described above, for example, in the form of metal foams or aerogels. Non-porous particle trapping structures, if appropriately designed, can also lead to particle scattering and deceleration. Plastic and elastic deformation of the particle trapping structures, which are usually metallic but not necessarily porous, can reduce the particle velocity to zero; that is, the momentum of each impacting particle is completely absorbed by the particle trapping structure. Therefore, a suitably designed non-porous particle trapping structure can also absorb the particles and prevent their further propagation in the vacuum environment.

[0036] The combination of blocking, trapping, and gettering particles, particularly tin particles, can be adapted to the specific industrial process in which it is used. These three measures can be tailored to the size and shape of the particles, their velocity, and their specific angle of entry. The combination of these three measures can also be adapted to the operation of the system under specific vacuum conditions, flow rates, and / or source capacities of the respective process. The components used—i.e., the shields, particle trap structures, and getter surfaces or components—can be modularly mounted and disposable, or, depending on the degree of contamination, regenerable, meaning they can be reused as replacement parts that can be reprocessed. By replacing saturated particle trap structures or...By using remanufactured or replaced parts, the functionality of getter surfaces can be extended over the entire lifespan of the system. It may also be possible to achieve an integrated design using 3D printing technology.

[0037] The combination of the three vacuum technology concepts described above—namely, blocking, trapping, and gettering particles—is particularly advantageous because combining only two different concepts may not achieve the desired result. Even initially blocked and / or trapped particles can subsequently be reactivated by gases, such as hydrogen, or by mechanical action, leading to degradation of functional surfaces, especially mirror surfaces. However, by appropriately combining all three concepts, tin-induced contamination can be significantly reduced. This, in turn, reduces production losses caused by contamination. Specifically, the replacement of degraded mirrors, submodules, or systems can be reduced or avoided by preventing or delaying degradation as described above.Furthermore, the effort and costs of service measures can be reduced if the corresponding detachable components need to be remanufactured, upgraded, or replaced, for example, due to getter saturation. In addition, effort, time, and costs can be saved compared to solutions that require greater effort in the design and connection of more complex or thicker plate-shaped shields and / or getter plates. Other vacuum technology concepts, such as cryogenic pumps or getter pumps, can also be used to further reduce the concentration of contaminating particles.

[0038] 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.

[0039] drawing

[0040] Exemplary embodiments are shown in the schematic drawing and explained in the following description. Fig. 1 schematically shows a projection exposure system for EUV projection lithography in a meridional section.

[0041] Fig. 2a-c schematic representations of the blocking, trapping and binding of contaminating tin particles,

[0042] Fig. 3 shows a schematic representation of a detail of the projection exposure system of Fig. 1 with a housing in which porous particle trapping structures are attached to an inner side of a wall of the housing, as well as

[0043] Fig. 4 shows a schematic representation of a detail of a housing in the form of an enclosure, which encapsulates the beam path, in which a porous particle trapping structure is incorporated in a wall of the housing, through which a gas flows.

[0044] In the following description of the drawings, identical reference symbols are used for identical or functionally equivalent components.

[0045] The following section describes, with reference to Fig. 1, the essential components of an optical arrangement for EUV lithography in the form of a projection exposure system 1 for microlithography. The description of the basic structure of the projection exposure system 1 and its components is not intended to be restrictive.

[0046] One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, a lighting optic 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the lighting system. In this case, the lighting system does not include the light source 3.

[0047] A reticule 7 located in the object field 5 is illuminated. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in one scanning direction, via a reticule displacement drive 9.

[0048] Figure 1 shows a Cartesian xyz coordinate system for illustrative purposes. The x-direction runs perpendicular to the plane of the drawing. The y-direction runs horizontally, and the z-direction runs vertically. In Figure 1, the scan direction runs along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0049] The projection exposure system 1 comprises a projection system 10. The projection system 10 serves to image the object field 5 onto an image field 11 in an image plane 12. A structure on the reticulum 7 is imaged onto a light-sensitive layer of a wafer 13 located in the image plane 12 within the area of ​​the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, particularly along the y-direction, via a wafer transfer drive 15. The displacement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized with each other.

[0050] Radiation source 3 is an EUV radiation source. Specifically, radiation source 3 emits EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation has a wavelength in the range between 5 nm and 30 nm. Radiation source 3 can be a plasma source, for example, an LPP source (laser-produced plasma) or a DPP source (gas-discharged produced plasma). It can also be a synchrotron-based radiation source. Radiation source 3 can be a free-electron laser (FEL).

[0051] The illumination radiation 16 emanating from the radiation source 3 is focused by a collector mirror 17. The collector mirror 17 can be a collector mirror with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector mirror 17 can be illuminated by the illumination radiation 16 at grazing incidence (Gl), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector mirror 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0052] After the collector mirror 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the radiation source 3 and the collector mirror 17, and the illumination optics 4.

[0053] The illumination optics 4 comprise a deflecting mirror 19 and, downstream of this in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with an effect that influences the beam beyond the mere deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. The first faceted mirror 20 comprises a plurality of individual first facets 21, which are also referred to as field facets in the following. Only a few of these facets 21 are shown by way of example in Fig. 1. Downstream of the first faceted mirror 20 in the beam path of the illumination optics 4 is a second faceted mirror 22. The second faceted mirror 22 comprises a plurality of second facets 23.

[0054] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (fly's eye integrator). With the aid of the second faceted mirror 22, the individual first facets 21 are imaged into the object field 5. The second faceted mirror 22 is the last beam-shaping, or indeed the last, mirror for the illumination radiation 16 in the beam path before the object field 5.

[0055] The projection system 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0056] In the example shown in Fig. 1, the projection system 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have an aperture for the illumination radiation 16. The projection system 10 is a double-obscured optical system. The projection optics 10 have an image-side numerical aperture greater than 0.4 or 0.5, and which can also be greater than 0.6, for example, 0.7 or 0.75.

[0057] The mirrors Mi, like the mirrors of the illumination optics 4, can have a highly reflective coating for the illumination radiation 16. During operation of the projection exposure system 1 shown in Fig. 1, the problem arises that, among other things, tin particles 24a in solid, liquid, and / or gaseous form are generated by the radiation source 3, which is an LPP source. These particles penetrate the illumination optics 4 of the EUV projection exposure system 1 through an intermediate focus ZF, as indicated in Fig. 2a, where the collector mirror 17 has been omitted for clarity. The tin particles 24a can reach the optical components in the form of the deflecting mirror 19 and the two faceted mirrors 20, 21 of the illumination optics 4 and contaminate them, resulting in a reduction of their reflectivity.

[0058] To remove the tin particles 24a in solid, liquid and / or gaseous form as well as tin particles 24b in the form of gaseous tin compounds, in particular tin hydrides SnH x To prevent the formation of the hydrogen present in the environment from the optical components 19, 20, 21 of the illumination optics 4 and from the optical components of the projection optics 10 in the form of mirrors M1 to M6, three different measures can be carried out individually or in combination, which are described below in connection with Fig. 2a-c.

[0059] Fig. 2a shows a beam path 25 of the illumination radiation 16 before and after the intermediate focus ZF. In Fig. 2a, the tin particles 24a are mechanically blocked by means of a shield 26 in the form of a shielding plate, which is arranged outside the beam path 25 and surrounds it in a ring-like manner or limits it laterally. With the aid of the shield 25, tin particles 24a located within the beam path 25 cannot be prevented from passing into the illumination optics 4, as can be seen in Fig. 2a. Fig. 2b shows another possibility for reducing the number of tin particles 24a in the form of particle trapping structures 27, 29. In Fig. 2b above, a particle trapping structure 27 is shown, which consists of an arrangement of metal sheets or...consisting of a metal grid with a plurality of metal sheets 28 arranged in a labyrinth-like pattern to scatter and decelerate the tin particles 24a, 24b, ideally reducing the momentum of the tin particles 24a, 24b to zero.

[0060] Such deceleration of the particles 24a, 24b can be achieved particularly advantageously with the aid of the porous particle trapping structure 29, which is shown below in Fig. 2b. The porous particle trapping structure 29 is formed in Fig. 2b in the form of a metal foam, more precisely an open-cell metal foam, which makes it possible to reduce the velocity of the tin particles 24a, 24b to zero over a comparatively short deceleration distance.

[0061] As shown in Fig. 2c, it is also possible, in particular tin particles 24b, which are in the form of tin compounds, e.g. in the form of gaseous tin hydrides, SnH xThe gas-binding material 30 is to be chemically bound to a gas-binding material 30. The gas-binding material 30 can be formed on the surface of a gas-binding component made of a gas-binding material, but it is also possible that the gas-binding material 30 is applied as a coating to a surface 31a of a component 31 that is not itself made of a gas-binding material. In particular, ruthenium, rhodium, nickel, palladium, or compounds of these materials can be used as gas-binding materials for tin particles 24a, 24b. The component 31 can, for example, be one of the metal sheets 28 of the particle trapping structure 27 or the porous particle trapping structure 29. The porous particle trapping structure 29 can be made of a gas-binding material, e.g., nickel, ruthenium, or possibly rhodium, or be coated with a gas-binding material, e.g.,with nickel or with palladium to enhance the gas-binding effect on the tin particles 24a, 24b.

[0062] Instead of an open-cell metal foam, the porous

[0063] The particle trapping structure 29 of Fig. 2b can also be configured as an aerogel, in particular as a metal oxide aerogel or a metallic aerogel. The metal oxide of the metal oxide aerogel can, for example, be selected from the group comprising: aluminum oxide, chromium oxide, titanium oxide, zirconium oxide, tungsten oxide, and iron oxide and their combinations. The metallic aerogel can be configured as a gas-binding aerogel, for example as a ruthenium aerogel, a nickel aerogel, or a NiP aerogel, to bind the tin particles 24a, 24b.

[0064] Fig. 3 shows an optical assembly in the form of the illumination system 4, which comprises the three optical components 19, 20, 21 in the form of the deflecting mirror 19 and the two faceted mirrors 20, 21, arranged in a common housing 32, more precisely in an interior space 33 of the housing 32. The three optical components 19, 20, 21 each have a surface 19a, 20a, 21a facing the interior space 33, which is designed to reflect the illumination radiation 16. The porous particle trapping structure 29, which was described in more detail above in connection with Figs. 2b, c, is attached in the example shown to an inner surface 34a of a wall 34 of the housing 32. In the example shown, the porous particle trapping structure 29 consists of an open-cell metal foam which is detachably attached to the inside 34a of the wall 34 of the housing 32.The detachable fastening can be achieved by a screw connection, by attaching the porous particle trap structure 29 to a bracket, or in some other way. The detachable fastening allows the porous particle trap structure 29 to be replaced, for example, when its capacity for trapping tin particles 24a, 24b is exhausted. It is understood that the porous particle trap structure 29 can also be permanently connected to the inner surface 34a of the wall 34 of the housing 32. Furthermore, unlike what is shown in Fig. 3, the porous particle trap structure 29 does not have to cover only a portion of the inner surface 34a of the wall 34 of the housing 32. Rather, the porous particle trap structure 29, or several porous particle trap structures 29, for example in the form of mats or the like, can extend over the entire inner surface 34a of the wall 34 of the housing 32.

[0065] To ensure that as many tin particles 24a, 24b as possible are completely decelerated, the porous particle trapping structure 29 has a thickness d that is slightly greater than half the deceleration distance of the tin particles 24a, 24b. The thickness d of the porous particle trapping structure 29 can be, for example, between 1 mm and 20 mm, and in particular between 5 mm and 10 mm. In the example shown in Fig. 3, the back side of the porous particle trapping structure 29 abuts the gas-tight inner surface 34a of the wall 34 of the housing 32. If the porous particle trapping structure 29 is made of an aerogel, it is generally applied to a substrate made of a gas-tight material and forms a structural unit with it, which is attached to or fastened to the inner surface 34a of the wall 34 of the housing 32.

[0066] The optical assembly 4 shown in Fig. 3 includes a heating device 35 for heating the porous particle trapping structure 29. The heating device 35 is designed to heat the porous particle trapping structure 29 to a temperature T that is higher than the melting point Ts of tin. This allows the tin particles 24a, 24b impacting the porous particle trapping structure 29 to remain liquid or to liquefy and be bound to the porous particle trapping structure 29 by alloying and subsequent solidification. To achieve this, it is advantageous if the typically open-cell metal foam of the porous particle trapping structure 29 is made of, or coated with, a material that alloys with tin or whose solderability with tin is considered good. The material could be, for example, silver, gold, palladium, rhodium, or nickel.

[0067] As can also be seen in Fig. 3, the housing 32 is a first, outer housing 32 in which a second, inner housing 32' is arranged, which serves to encapsulate the beam path 25 of the illumination radiation 16. The inner housing 32' encapsulates the entire beam path 25 within the outer housing 32 and has a surrounding wall 34'. For the sake of simplicity, only a section of the inner housing 32' is shown in Fig. 3, which runs between the intermediate focus ZF and the deflecting mirror 19.

[0068] A porous particle trapping structure 29' is also attached to the inner wall 34' of the inner housing 32', which is designed like the porous particle trapping structure 29 on the wall 34 of the outer housing 32, or as shown in Fig. 2b, c. The particle trapping structure 29' on the inner wall 34' of the inner housing 32' can also be heated by means of a heating device. It is understood that, as an alternative to the representation in Fig. 3, only one of the two particle trapping structures 29, 29' can be provided in the optical assembly 4.

[0069] Fig. 4 shows an optical assembly 4' comprising the deflecting mirror 19, the inner housing 32' with an interior space 33' formed therein, and a porous particle trapping structure 29' in the form of an aerogel, e.g., made of NiP. Unlike in Fig. 3, the porous particle trapping structure 29' in Fig. 4 is embedded in the wall 34' of the inner housing 32'. A first side 29a' of the porous particle trapping structure 29' faces the interior space 33' of the inner housing 32'. On a second side 29b' of the porous particle trapping structure 29', facing away from the interior space 33', there is a suction device in the form of a Venturi nozzle 36. The Venturi nozzle 36 draws gas, for example, in the form of molecular hydrogen H₂, from the interior space 33' of the inner housing 32'.The Venturi nozzle 36 is part of a supply device 37 in the form of a gas line for supplying molecular hydrogen H₂ to the interior 33' of the inner housing 32', which exits at an outlet opening 38 on the wall 34' of the inner housing 32'. A gas flow is generated in the interior 33' between the outlet opening 38 and the porous particle trapping structure 29' or the intake device in the form of the Venturi nozzle 36. The tin particles 24a, 24b are carried along in the gas flow and transported to the porous particle trapping structure 29', through which the hydrogen gas from the interior 33' flows. Here, the tin particles 24a, 24b are trapped in the material of the porous particle trapping structure 29, which acts like a filter.

[0070] Alternatively or additionally, the porous particle trapping structure 29' described in connection with Fig. 4 can be incorporated into the wall 34 of the outer housing 32 of Fig. 3. The suction device 36 and the feed device 37 can also be integrated into the wall 34 of the outer housing 32. When the porous particle trapping structure 29' is incorporated into the wall 34 of the outer housing 32, the feed device 37 can generally be implemented more easily than when the porous particle trapping structure 29' is incorporated into the wall 34' of the inner housing 32'.

[0071] Although the above examples describe contaminating particles in the form of tin particles 24a, 24b, which are kept away from the surfaces 19a, 20a, 21a of the optical components 19, 20, 21 of the illumination system 4, it is also possible to capture other types of contaminating particles using the porous particle trapping structures 29 described above. In particular, the type of gas-binding material used can also be adapted to the type of particles.

Claims

Patent claims 1. Optical assembly (4, 4') for a semiconductor lithography system, in particular for a projection exposure system (1), comprising: at least one housing (32, 32') with an interior (33, 33'), and at least one optical component (19, 20, 21) having a surface (19a, 20a, 21a) facing the interior (33, 33'), characterized in that the optical assembly (4, 4') has at least one porous particle trapping structure (29, 29') arranged on an inner surface (34a, 34a') of a wall (34, 34') of the housing (32, 32') or incorporated in the wall (34') of the housing (32') for trapping contaminating particles (24a, 24b) present in the interior (33, 33').

2. Optical assembly according to claim 1, wherein the porous particle trapping structure (29, 29') is attached to a gas-tight component, preferably to the wall (34, 34') of the housing (32, 32'), wherein the housing (32') is designed in particular to encapsulate a beam path (25).

3. Optical assembly according to claim 1 or 2, wherein the porous particle trapping structure (29, 29') is detachably connected to the inside (34a, 34a') of the wall (34, 34') of the housing (32, 32').

4. Optical assembly according to one of the preceding claims, wherein the porous particle trapping structure (29, 29') is formed from an aerogel.

5. Optical assembly according to claim 4, wherein the aerogel is configured as a metal oxide aerogel or as a metallic aerogel, wherein the metal oxide of the metal oxide aerogel is preferably selected from the group comprehensive: aluminum oxide, chromium oxide, titanium oxide, zirconium oxide, tungsten oxide, molybdenum oxide, hafnium oxide and iron oxide.

6. Optical assembly according to claim 4 or 5, wherein the aerogel is designed as a gas-binding aerogel, preferably as a ruthenium aerogel, as a nickel aerogel or as a NiP aerogel.

7. Optical assembly according to one of claims 1 to 3, wherein the porous particle trapping structure (29, 29') is formed from a metal foam, in particular from an open-cell metal foam.

8. Optical assembly according to claim 7, wherein the metal foam is formed from a gas-binding material and / or coated with a gas-binding material, wherein the gas-binding material is preferably selected from the group comprising: Ru, Ni, Rh, Pd, Pt.

9. Optical assembly according to one of the preceding claims, further comprising: a heating device (35) for heating the porous particle trapping structure (29), in particular the metal foam, to a temperature (T) that is greater than the melting temperature (Ts) of tin.

10. Optical assembly according to claim 9, wherein the metal foam is formed from a material and / or coated with a material that forms an alloy with tin.

11. Optical assembly according to one of the preceding claims, wherein the porous particle trapping structure (29, 29') has a thickness (d) between 1 mm and 20 mm, preferably between 5 mm and 10 mm.

12. Optical assembly according to one of claims 1 or 3 to 11, wherein the porous particle trapping structure (29') is located in the wall (34') of the housing (32') is included and an intake device (36), in particular a Venturi nozzle, for drawing gas (H2) from the interior (33') is attached to a side (29b') of the porous particle trapping structure (29') facing away from the interior (33'), in particular in the wall (34') of the housing (32').

13. Optical assembly according to claim 12, wherein the intake device (36) is integrated into a supply device (37) for supplying a gas (H2) to the interior space (33').

14. Semiconductor technology system, preferably projection exposure system (1), in particular for EUV lithography, comprising: at least one optical assembly (4, 4') according to one of the preceding claims.

15. Semiconductor technology system according to claim 14, further comprising: a shield (26) for blocking contaminating particles (24a, 24b) arranged outside a beam path (25) of the semiconductor technology system (1 ).

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