Conversion layers to block outgassing in hydrogen plasma

Abstract

A component for EUV lithographic apparatus comprises: a) a component core made of a material comprising i) at least a first metal Me or a Me-alloy core and ii) a contaminant X which is susceptible to form volatile compounds that outgas within an EUV lithographic apparatus environment, and b) a capping layer provided on the top of the core and forming an outer surface arranged to be in contact with the environment within the lithographic apparatus, wherein the capping layer comprises an oxide YO of a second metal Y, and wherein the second metal Y is selected such as at working temperature to chemically react with the X' contaminant atoms which diffuse from the core to the capping layer and towards the outer surface of the components, forming thereby an alloy X'Y within the capping layer such that substantially all the diffusing X' contaminant is bound in the capping layer.

Description

CONVERSION LAYERS TO BLOCK OUTGASSING IN HYDROGEN PLASMACROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23220121.0 which was filed on 22 December 2023, and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to conversion layers to block outgassing in a EUV induced H plasma in materials, especially for a lithographic apparatus. The invention yet also relates to a method for preventing deposition of contaminants on an lithographic component and / or refurbishing of the lithographic component.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] A disadvantage of using EUV radiation is that EUV radiation is easily absorbed by other materials. These materials may be gases in the optical path of the EUV radiation or contamination of optical components in the optical path of the EUV radiation, which can also deposit as a layer on various surfaces including optical components such as EUV mirrors and on other optical surfaces. Hence, to reduce EUV absorption, the lithographic apparatus is preferably operated at a pressure well below atmospheric pressure, e.g. (near) vacuum conditions, to reduce absorption by gases in the optical path of the EUV radiation, and deposition of undesired species on the optical components is preferably prevented or at least minimized. In order to prevent, or at least minimize, deposition of undesired species, a gas may be added such as hydrogen gas. The EUV radiation will form a plasma by ionizing and / or dissociating the hydrogen gas. The resulting hydrogen radicals and ions are then able to etch various materials, e.g. silicon (Si) and phosphor (P), by forming volatile hydrides. However, some materials used in optical components are active catalytic materials meaning that volatile hydrides preferably decompose on the surfaces of the optical components, thereby reducing EUV reflectivity, and may also subsequently oxidize, thereby further reducing EUV reflectivity.

[0006] In a lithographic apparatus there may be many components and for each there may be several materials used for manufacturing the components. Such components may further be subjected to various gases such as H2, 02, water vapours or N2. Due to EUV induced plasma there are H, O and N plasma species created with result in various degradation mechanisms, for example etching and outgassing, contamination with volatile species, blistering and delamination, or embrittlement. Contaminants such as volatile species and hydrogen induced outgassing is also called HIO .

[0007] Hence, despite the presence of hydrogen gas, the layer of contaminants may grow until there is a dynamic balance between deposition and etching resulting for example in a saturation of the reflectivity loss. Diffusion of radicals, chemical etching and formation of volatile species are undesirable and there is a need to find robust construction materials and surface treatments to plasma. Such materials provide no EUV radiation transmission losses and implicitly high yield and throughput.SUMMARY

[0008] Considering the above, it is an object of the invention to provide robust construction materials and surface treatments for manufacturing lithographic components which are resistant to EUV plasma.

[0009] According to an aspect, there is provided a component for EUV lithographic apparatus comprising: a) a component core made of a material comprising i) at least a first metal Me or a Me- alloy core; and ii) a contaminant X which is susceptible to form volatile compounds that outgas within an EUV lithographic apparatus environment; and b) a capping layer provided on the top of the core and forming an outer surface arranged to be in contact with the environment within the lithographic apparatus, wherein the capping layer comprises an oxide YO of a second metal Y, and wherein the second metal Y is selected such as at working temperature to chemically react with the X’ contaminant atoms which diffuse from the component core to the capping layer and towards the outer surface of the component, forming thereby an alloy X’Y within the capping layer such that substantially all the diffusing X’ contaminant is bound in the capping layer. By substantially all the diffusing contaminant X’ herein is mean at least 95wt%, preferably at least 98% wt% of the diffused amount of X in the capping layer.

[0010] Herein by contaminant X in the component core is to be understood to include traces of undesired contamination atoms, but it may also be a constituent element that is part of the Me-alloy itself (i.e. one of the alloy constituents which is not the first metal Me). Herein contaminant X’ is meant to be atoms of contaminant X which diffuse from the component core to the capping layer and towards the outer surface of the component (i.e. X and X’ are the same type of atoms).

[0011] Between the component core and the capping layer also an intermediate layer may be present, for example to ensure better adhesion between the core component and the capping layer. In such case the contamination X atoms will first diffuse from the component core through the intermediate layer and then towards the capping layer. This is the same as to say that the capping layer may be formed by multiple layers, wherein at least one layer contains the second metal Y that forms an alloy withcontaminant X’ atoms that diffuse through that layer. Therefore the capping layer may be also covered with an additional layer if needed for a specific functionality such as protection.

[0012] The first metal Me may be prone to chemically alloy with “contaminant” X at working temperature in the scanner.

[0013] The second metal Y may be any metal which chemically alloys, at the working temperature to the HIO outgassing contaminant X’ diffused into the capping layer. Examples are Ni, Cu, Cs but any other suitable metal is envisaged herein.

[0014] The second metal alloy may be in contact with the component surface, or alternatively, with an intermediate layer through which X’ can diffuse to reach the capping layer YO. An example of such intermediate layer is NiP, which layer ensures the adhesion of the YO (e.g. NiO) coating to the component core.

[0015] The capping layer may also include therefore an intermediate layer added for example for improved adhesion.

[0016] The EUV lithographic apparatus environment may be a Hydrogen plasma environment. However, other gases may be used. The plasma is induced by the EUV radiation passing through the gas.

[0017] The material of the component core may comprise as first metal Me for example a metal selected from Al, Mg, Zn, Pb, Cu, or alloys therefrom. For example, the first metal Me may be aluminium Al, whereas the first metal alloy is an aluminium alloy such as A15083.

[0018] The capping layer is also called herein a (HlO)-barrier coating. The capping layer comprises for example NiO, CuO, CsO2 or alloys thereof.

[0019] The X contaminant in the component core or the X’ contaminant diffused from the component core into the intermediate layer of the capping layer is for example Magnesium Mg or Zinc Zn.

[0020] The second metal Y is selected from the list of Ni, Cu, Cs which form as oxides NiO, CuO, CsOi.. The outer surface of the capping layer may become under the effect of the EUV induced plasma a reduced metallic layer Y. Such a reduced metallic layer Y formed in the lithographic plasma environment substantially comprises the second metal Y devoid of oxygen (or with trace amounts).

[0021] The capping layer has a total thickness for example from 1 nm to 10 microns.

[0022] In another embodiment there is provided a method to reduce outgassing of a contaminant X from a lithographic component, the method comprising: 1) providing a metal oxide YO capping layer on the core surface of a component, the capping layer YO having an inner and an outer surface, wherein the inner surface is in contact with the component core surface and the outer surface of the capping layer is in contact with a lithographic environment; 2) reducing the surface of the metal oxide YO capping layer in H plasma environment to a metallic compound Y, such that outgassing atom or molecular species X’ passing from the component core through the capping layer will alloy with compound Y reduced in the plasma environment to form an X’Y alloy, thereby X’ becoming chemically bonded within the capping layer before reaching the outer surface of the capping layer.

[0023] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2 depicts the coating principle according to the invention: a) in conditions of no EUV plasma, b) in the presence of EUV plasma;Figure 3 depicts a histogram showing the magnesium (Mg) outgassing rate, as measured with x- ray photoemission spectroscopy (XPS) in atomic % and on a logarithmic scale, for: (i) bare aluminium; (ii) aluminum coated with nickel oxide (NiO) as example of YO coating and with a nickel phosphorous (NiP) as intermediate layer between NiO (YO) and the Me or Me-alloy, through which Mg diffuses (i.e. the X’ contaminant atoms).DETAILED DESCRIPTION

[0025] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0026] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0027] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning deviceMA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13, 14 in Figure 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0028] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0029] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS.

[0030] The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source that is capable of generating EUV radiation.

[0031] The present disclosure relates to improvements to a lithographic system, especially to components of lithographic apparatus such as EUV lithographic apparatus. The lithographic system may, for example, be an extreme ultraviolet (EUV) lithographic system that comprises an EUV radiation source SO and a lithographic apparatus LA or an inspection or metrology tool which uses EUV radiation.

[0032] Some parts or components of EUV lithographic systems are formed from metals and metal alloys, such as aluminium and aluminium alloys, since such alloys are suitable for easy machinability of large parts. For example, the mirror frames, parts or components of a lithographic system, or even the vessel walls within a lithographic system may be formed from such metal or metal alloy materials.

[0033] EUV lithographic systems are typically operated under near-vacuum conditions (i.e. at pressures well below atmospheric pressure). In addition, it is common to provide hydrogen gas within EUV lithographic systems, particularly in the vicinity of optical components (for example the illumination and projection optics). Such components may further be subjected to various gases such as H2, 02, water vapours or N2. Due to EUV induced plasma there are H, O and N plasma species created which result in various degradation mechanisms, for example etching and outgassing, contamination with volatile species, blistering and delamination, or embrittlement. Contamination with volatile species and outgassing form a HIO type outgassing. HIO type outgassing elements may be eliminated in a plasma environment from such parts inside the lithographic EUV machine. Hydrogen plasma induced outgassing can then induce contamination of critical parts like mirrors, reticles, sensors etc.

[0034] It has been found that it is beneficial to coat parts or components of EUV lithographic systems formed from metals and metal alloys with a range of materials that, coated on the alloy-based surfaces, may not only provide protection as a mechanical or anti-diffusion barrier, but it may also chemically bind contaminant atoms and keep them stored inside as a chemical barrier. It has also been found that such contamination binding coatings may result from activating a chemical reaction between the metal(oxide) of the parts or components and the outgassing (contaminating) element, which only works (i.e. it gets activated) under (EUV-induced) plasma conditions.

[0035] For example, a portion of the interior walls of the lithographic system proximate the EUV optics may be coated with (HlO)-barrier coating as a capping layer to prevent hydrogen-induced outgassing from those portions. The HlO-barrier coating may comprise for example NiO. In such case the interior walls are an example of what is herein referred to as component core.

[0036] Referring to FIG. 2, a portion of a vacuum chamber forming the EUV optics environment (e.g. one or more walls of the vacuum chamber) and that faces the same gas environment as the EUV mirrors (e.g. active species of hydrogen during cleaning) may be made of, or coated with a hydrogen- induced outgassing (HlO)-barrier material. Such HlO-barrier coating may not contain at all contamination elements X’ or it may have a concentration less than a threshold (e.g. less than 1%, preferably less than 0.1%) of any of contamination elements X’ that form volatile species with hydrogen ions or radicals or have a low sputtering threshold. In some embodiments, the material for the capping layer which forms a HlO-barrier coating may include NiO. In some embodiments, a significant portion of the EUV optics environment (e.g., >50% of all surfaces facing the same environment as EUV optics environment) may be coated with a HlO-barrier coating.

[0037] Critical areas may include any areas within 30 cm from or with a line of sight to any of the reflecting surfaces, or any alloyed parts containing elements with lower sputtering threshold than that of the material of the protective coating for the EUV gas environment or cleaning environment (e.g., Al, Mg, Zn, Pb, Cu, or other elements) are also coated with the above coating.

[0038] A surface of a part or component comprising a metal or metal alloy may be treated therefore with a coating configured to chemically bind the atoms or molecules of a contaminant inside the coating.

[0039] By promoting the binding of a contaminant to a coating on the surface of the part, it is possible to reduce the likelihood of contaminant species to diffuse outside the layer, becoming volatile and drift away, in order to avoid such contaminant species to become incident on other critical surfaces where they may cause damage and reduction of EUV reflection / transmission.

[0040] The coating material forming the capping layer may comprise one or more metals in an oxidized form or as an alloy, such as NiO, CuO, CsO2 or alloys thereof.

[0041] The coating may have a thickness of between Inm and 10pm. In particular, the coating may preferably have a thickness of between lOnm and 1 m. The thickness of the coating may be selected to minimize the possibility of the coating peeling away from the surface of the component. In this way, generation of contaminant species originating from the coating is minimized.

[0042] It will be appreciated that various parts and components may be provided with coatings having different properties, depending on their material composition. For example, a first component may be provided with a first coating which is, for example, a coating comprising a first HlO-barrier material. A second component may be provided with a second coating which is, for example, a coating comprising a second HlO-barrier material that is different from the first HlO-barrier material.

[0043] It has been found that contaminant particles may be inhibited from drifting around the vessel by providing a suitable HlO-barrier coating. For example, after the coating has been applied to a part, the coating may be further treated (e.g. subjected to a plasma) in order to promote reaction between materials. The coating may be provided in multiple layers.

[0044] In particular, the thickness of the coating may be chosen to minimize the possibility of the coating peeling away from the part surface. The coating may have a substantially uniform thickness along the length of the part or component. Alternatively, the coating may have a thickness which varies along the length of the part or component.

[0045] The coatings described above promote chemical binding of contaminant atoms inside the HlO-barrier layer. This binding prevents the contamination species from becoming airborne and / or drifting around the environment surrounding the parts. In a lithographic apparatus, this is particularly desirable since drifting particles may end up settling on and / or damaging sensitive components, such as optical components, of the apparatus.

[0046] The HlO-barrier coating material of the capping layer is a metal oxide, YO (wherein Y is a metal), chosen such that:- Is chemically reduced under EUV radiation (under H plasma), and- It chemically alloys with a potentially contaminant outgassing element X (or X’) at the room / working temperature.

[0047] Figure 2 (left side) shows a part of a component core as a base layer made of a Me alloy and a capping layer YO on the top in the absence of the EUV radiation and H plasma. Figure 2 (right side) shows that in the presence of H plasma (EUV lithography tool) the metal oxide YO becomes reduced to its metallic form Y close to the surface due to the interaction of the metal oxide YO with the hydrogen plasma, and element X from the Me-alloy diffuses towards the surface. When X (for example Mg) from the underlying (Al) alloy diffuses through the metal oxide coating, and reaches the surface, it will interact with the reduced metal (e.g.. Ni), and will then alloy with it (at room temperature), and not diffuse further towards the surface due to this alloying effect of the Mg-metal (at room temperature).

[0048] This chemical conversion HlO-barrier layer suitable to prevent for example the outgassing of Mg works for metals which alloy with Mg at room temperature (RT), like Ni, Cu, Sn, or at any other working temperature specific in the lithographic apparatus during use. Examples of such coatings are: NiO, CuO, CsCh and alike where Mg would be “stored” by chemically binding (alloying) inside the coating and prevented from outgassing.

[0049] This principle is generally valid for any outgassing element (like Mg, Zn,etc) which alloys with the metal (from the oxide coating) at RT or at any other working temperature. It is therefore envisaged to coat the part made of an alloy containing element X with a metal (Y) oxide, YO, and the element Y should be chosen such that it alloys with the element X. Under H plasma environment (in a functioning EUV lithography system) two processes will occur:1) The surface of the metal oxide interacting with the H plasma will become metallic (metal oxide reduced by the H).2) The element X in the alloy will diffuse towards the surface of the metal oxide YO (from the inside, the diffused X element being noted as X’).

[0050] As a consequence of process 1) the reduction of the oxide to a metal (Y) and process 2) the diffusion of the element X’ towards the surface, the element X’ diffusing to the surface will react with Y to form and alloy X’ Y. This alloying will immobilize the further diffusion of X’ towards the surface and therefore will prevent the outgassing of element X (and the contamination of lithographic components). The coating YO acts as like a “sponge” of outgassing elements in the sense that it accumulates and binds the element X’ selectively inside it, only under a H plasma environment, blocking the outgassing.

[0051] For example, it has been found that such first metals may also contain magnesium Mg which can outgas, resulting in contamination in the lithographic system. It has been found that coating of such components / materials with NiO or another suitable metal oxide on the top of a component core material will provide diffusion of Mg through the (NiO) coating, such that Mg atoms will alloy with Ni from the inside surface (i.e. before reaching the outer NiO coating surface). Ni in a metal oxide coating NiO becomes under H plasma conditions a metallic material Ni and favours alloying with Mg before the Mg reaches the surface and outgasses. As a consequence, Mg cannot gas out since it is chemically bound (alloyed) to the Ni-based coating. With other words, alloying happens at the NiO coating, which gets activated to Ni (metallic) in the presence of the H plasma.

[0052] State of art NiO coatings are not prone in itself to form such an alloy, the action of H plasma is also needed to induce the alloying reaction with Mg. Similarly to the option of using contamination getters for HIO contamination near sensitive optical components with scope to bind molecules, the present invention provides that binding is happening from inside of the coated component rather than (reacting) from outside (e.g. by chemical or Van de Waals adhesion to a surface).

[0053] It is envisaged herein a method to reduce (Mg) outgassing by: 1) providing a metal oxide coating having an inner and an outer surface, the inner surface in contact with the component surface; 2) reducing the metal oxide coating in H plasma environment to a metallic compound, such that outgassing molecules will alloy with the material reduced in the H plasma from the inner surface side and become chemically bonded before reaching the outer surface side.

[0054] The method provides to reduce outgassing of a contaminant X from a lithographic component, the method comprising: 1) providing a metal oxide YO capping layer on the core surface of a component, the capping layer YO having an inner and an outer surface, wherein the inner surface is in contact with the component core surface and the outer surface of the capping layer is in contact with a lithographic environment; 2) reducing the surface of the metal oxide YO capping layer in H plasma environment to a metallic compound Y, such that outgassing atom or molecular species X’ passing from the component core through the capping layer will alloy with compound Y reduced in the plasmaenvironment to form an X’Y alloy, thereby X’ becoming chemically bonded within the capping layer before reaching the outer surface of the capping layer.

[0055] The blocking effect of a potentially outgassing element (eg. Mg in A15083) in a hydrogen plasma environment by a metal oxide is provided herein as an example. The blocking mechanism relies in using the alloying properties between the outgassing element and the metal coating, inhibiting the outgassing element to reach the surface and therefore outgas.

[0056] It is known that the aluminium or other suitable materials used for the wall and frames of the scanners components are sources of Si- and Mg- based HIO in form of volatile compounds. The proposed improvement is to overcoat all of the parts of the component core. This will have a double effect: it will remove a major HIO source and secondly the getter surface area will increase.

[0057] However, when applying a (galvanic) Ru / Ni coating on aluminium the coating may have a poor adhesion due to the presence of the native oxide skin on the aluminium. This skin needs to be removed first and then the surface needs to be stabilized. This is done for example by a applying a very thin Zink layer promoting the adhesion of the subsequent Ru and / or Ni coating. However, the zinc is in itself a HIO material. In case of scratch etc of the Ru / / Ni overcoating the zinc adhesion layer will be exposed to plasma and the HIO risk is increased instead of decreased. The invention discussed herein provides a coating method without the need for a zinc adhesion layer.

[0058] Under H plasma conditions the metal oxide close to the surface region is partially reduced to its metallic oxidation state due to the interaction with the hydrogen plasma. As a consequence of the plasma exposure (and H diffusion), the outgassing element diffuses towards the surface of the metal oxide coating. The outgassing element and the reduced metal close to the surface, will form an alloy, which will then prevent the element to further diffuse towards the surface. Since the potentially outgassing element is alloyed (chemically bonded) with the metal, it won’t reach the surface nor outgas (nor contaminate mirrors or other sensitive optical components).

[0059] The present disclosure relates to coatings for components formed from aluminium alloys and components formed from aluminium alloys that are provided with such coatings. In particular, the present disclosure relates to components for use in an EUV lithographic apparatus (or any environment in which an EUV-induced hydrogen plasma may be present).

[0060] The magnesium outgassing rate for aluminium coated with zirconium oxide was of two orders of magnitude lower than that of the bare aluminium. Furthermore, the magnesium outgassing rate for the aluminium coated with chromium oxide was below the detection limit of the XPS.

[0061] In another embodiment, it is proposed to coat components formed from an aluminium alloy with a metal nitride or a metal phosphide, for example nickel oxide (NiO) to prevent or decrease significantly the outgassing of HIO elements from aluminium alloys. This modified coating alloys with elements from the aluminium alloy (such as magnesium) before they reach the surface. The magnesium diffuses through the NiO coating but, before it reaches the surface, it alloys with the (chemically reduced) nickel in the coating (as a result of interaction with H plasma). Furthermore, under thehydrogen plasma conditions this alloy of magnesium and nickel is metallic in the surface region in contact with H plasma. As a consequence, magnesium cannot reach the surface of the sample since it is chemically bound to the coating.

[0062] Furthermore, a coating of Ni (in its metallic form) or its oxide NiO is a good getter for elements like magnesium, which may have been outgassed from other sources within the lithographic apparatus. Such outgassed volatiles comprising magnesium will stick on the surface of the NiO coated component.

[0063] Figure 3 is a histogram showing the magnesium (Mg) outgassing rate, as measured with x-ray photoemission spectroscopy (XPS) in atomic % and on a logarithmic scale, for: (i) bare aluminium; (ii) aluminum coated with nickel phosphorous (NiP) and NiO on the top. As can be seen from Figure 3, the magnesium outgassing rate for aluminium coated with nickel phosphorous (NiO) is at least two orders of magnitude lower than that of the bare aluminium. Figure 3 shows how the use of a NiO / NiP coating improves the outgassing rate by a factor of xlOO with NiO coating. The Mg still detected is within the background contamination level of the experimental equipment.

[0064] It has been proved experimentally that a sample of aluminium alloy coated on the top with NiO and NiP intermediate layer, after exposure to the plasma, shows that magnesium accumulates close to the surface of the sample but does not reach the surface of the sample.

[0065] Further experimental results shown in figure 3 proved that the percentage of magnesium outgassed as a function of exposure time is significantly reduced for aluminium coated with nickel oxide (NiO / NiP / Al) relative to a sample of bare aluminium (bare Al).

[0066] Other type of coatings may also be viable for suppressing the magnesium outgassed from aluminium alloys. However, some other materials may be prone to delamination when exposed to the EUV-induced plasma existing in the lithographic apparatus. In contrast, conversion coatings that form part of the chemistry of the surface of the alloy are less eligible for delamination and are therefore particularly suitable for use as coatings for components formed from aluminium alloys that are for use in an EUV lithographic apparatus (or any environment in which an EUV-induced hydrogen plasma may be present).

[0067] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin film magnetic heads, etc.

[0068] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (orother patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non- vacuum) conditions.

[0069] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A component for EUV lithographic apparatus comprising: a) a component core made of a material comprising i) at least a first metal Me or a Me-alloy core and ii) a contaminant X which is susceptible to form volatile compounds that outgas within an EUV lithographic apparatus environment, b) a capping layer provided on the top of the core and forming an outer surface arranged to be in contact with the environment within the lithographic apparatus, wherein the capping layer comprises an oxide YO of a second metal Y, and wherein the second metal Y is selected such as at working temperature to chemically react with the X’ contaminant atoms which diffuse from the component core to the capping layer and towards the outer surface of the component, forming thereby an alloy X’Y within the capping layer such that substantially all the diffusing X’ contaminant is bound in the capping layer.

2. A component according to claim 1 , wherein the EUV lithographic apparatus environment is a Hydrogen plasma environment.

3. A component according to claim 1 or 2, wherein the material of the component core comprises as first metal Me selected from Al, Mg, Zn, Pb, Cu, or alloys therefrom.

4. A component according to claim 3, wherein the first metal Me is aluminium Al or the first metal alloy is an aluminium alloys such as A15083.

5. A component according to any preceding claims, wherein the capping layer is (HlO)-barrier coating.

6. A component according to any preceding claims, wherein the capping layer comprises NiO, CuO, CsO2 or alloys thereof.

7. A component according to any preceding claims, wherein the X or X’ contaminant is selected from Magnesium (Mg) or Zinc (Zn) or mixtures thereof.

8. A component according to any preceding claims, wherein the second metal Y is selected from the list of Ni, Cu, Cs which form as oxides NiO, CuO, CsOz.

9. A component according to any preceding claims, wherein the outer surface of the capping layer is a reduced metallic layer formed in plasma environment substantially comprising the second metal Y substantially devoid of oxygen.

10. A component according to any preceding claims, wherein the capping layer has a total thickness from 1 nm to 10 microns.

11. A method to reduce outgassing of a contaminant X from a lithographic component, the method comprising: 1) providing a metal oxide YO capping layer on the core surface of a component, the capping layer YO having an inner and an outer surface, wherein the inner surface is in contact with the component core surface and the outer surface of the capping layer is in contact with a lithographic environment; 2) reducing the surface of the metal oxide YO capping layer in H plasma environment to a metallic compound Y, such that outgassing atom or molecular species X’ passing from the component core through the capping layer will alloy with compound Y reduced in the plasma environment to form an X’Y alloy, thereby X’ becoming chemically bonded within the capping layer before reaching the outer surface of the capping layer.

12. A lithographic apparatus or a lithographic tool comprising a component according of claims1 to 10.

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