Method for applying a getter material to a surface of a component and lithography system

Abstract

The invention relates to a method for applying at least one getter material (31, 32) to a surface (30) of a component (29) for a lithography system, in particular for an EUV lithography system, comprising: applying the at least one getter material (31, 32) to the surface (30) of the component (29) by laser cladding. The invention also relates to a lithography system, in particular an EUV lithography system, comprising: at least one component (29) having a surface (30) onto which at least one getter material (31, 32) is applied by laser cladding.

Description

Background of the invention

[0001] The invention relates to a method for applying at least one getter material to a surface of a component for a lithography system, in particular for an EUV lithography system. The invention also relates to a lithography system comprising at least one such component.

[0002] For the purposes of this application, an (EUV) lithography system is understood to mean an optical system that can be used in the field of (EUV) lithography. In addition to a projection exposure system for (EUV) lithography, which serves to manufacture semiconductor components, the lithography system can, for example, be an inspection system for inspecting a photomask used in such a projection exposure system (hereinafter also referred to as a reticle), for inspecting a semiconductor substrate to be structured (hereinafter also referred to as a wafer), or a metrology system used to measure a projection exposure system for (EUV) lithography or parts thereof, for example, for measuring projection optics.

[0003] In particular, optics of EUV lithography systems suffer from so-called hydrogen-induced outgassing products, also known as HIO (hydrogen-induced outgassing) products. HIO products are formed as products of a reaction between HIO-forming materials, e.g. in the form of Sn, Si, Zn, P, Mg, Pb, S, etc., with hydrogen excited by EUV radiation, which can be present, for example, in the form of hydrogen ions or hydrogen radicals. The HIO products can reach the surfaces of the optics via gas-phase transport, e.g. in the form of volatile hydrides, for example in the form of stannane, SnH4, or in the form of silane, SiH4, and deposit there, which leads to the formation of a contamination layer on the surface of the respective optic. This contamination layer leads to a reduction in the reflection of the optics of the lithography system, which are usually designed as reflective elements.

[0004] In addition to avoiding HIO-forming materials in the components of a lithography system and shielding components that contain HIO-forming materials, the introduction of HIO-binding surfaces, so-called getter surfaces, is a third pillar in HIO contamination prevention. One or more getter materials are applied to the getter surfaces to bind the HIO products. Getter surfaces can be formed, for example, on additional components, which are preferably arranged in the spatial proximity of HIO-forming materials and mirror surfaces within the lithography system. Getter materials are usually applied to a component surface in the form of getter coatings or individual layers of such a getter coating. The surface material to which such a getter coating is applied is often stainless steel.The getter coating is typically applied by electrochemical deposition.

[0005] Electrochemical deposition, however, generally requires pretreatment of the surface onto which the getter material is to be deposited. While this is generally possible without any problems with stainless steel surfaces, surfaces made of other materials, e.g., aluminum, require an additional pickling process to remove the surface oxide. The pickling process is generally based on a zinc pickling agent. However, since zinc itself is one of the HIO-forming materials, the use of getter materials on aluminum surfaces is currently not practiced. This is disadvantageous because the largest surfaces in the EUV optics of an EUV lithography system, both in the illumination optics and the projection optics, are formed on mechanical frame structures that contain aluminum or are made of aluminum.Thus, valuable getter surfaces are lost and with them a very large potential for further reducing the HIO-induced transmission loss.

[0006] A further disadvantage of electrodeposited layers is that large components require very large bath volumes, which results in high costs, especially for coatings with precious metals. Furthermore, housing components of EUV lithography systems, in particular, usually have a very complex three-dimensional geometry, which can lead to very different local layer thicknesses during electrodeposition processes.

[0007] In addition, coatings generally pose an increased risk of particle formation and the associated particle transport to the EUV mask: Hydrogen can penetrate the coatings, e.g., through diffusion, and the penetrated hydrogen can lead to reaction with foreign atoms and molecules at interfaces. The reaction products generally occupy a larger volume than the starting material, causing the layers to spall, resulting in the particle formation described above. Every particle deposited on the mask, measuring just a few nanometers, leads to imaging errors and thus to the loss of processed wafers. Object of the invention

[0008] An object of the invention is to improve the application of a getter material to a surface of a component for a lithography system. Subject of the invention

[0009] This object is achieved by a method of the type mentioned above, comprising: applying the at least one getter material to the surface of the component by laser deposition welding.

[0010] The inventors propose applying getter materials to the surfaces of components for lithography systems, specifically EUV lithography systems, using a laser cladding process. As can be seen from the Wikipedia article "Laser cladding," laser cladding is a type of cladding, in which a surface is deposited on a workpiece by melting and simultaneously applying almost any material. This can be done in powder form, such as metal powder, or with a welding wire or ribbon. In laser cladding, a high-power laser serves as the heat source, primarily a diode laser or fiber laser, but previously also CO2 and Nd:YAG lasers. The process can be used both to create layers and free-form 2.5D structures (laser generation). In the latter case, it can be classified as a 3D printing process.

[0011] Laser cladding thus makes it possible – as is common with welding processes – to permanently join two or more materials. This allows for efficient application of getter materials, particularly to the surfaces of large components, such as the supporting structures of optics or similar devices, even when these components may have complex geometries.

[0012] In one variant of the process, the component is made of stainless steel, aluminum, or an aluminum alloy, at least on its surface. In contrast to the electroplating process described above, the application of getter materials to an aluminum surface is readily possible using laser cladding. Laser cladding can therefore also be used to create getter surfaces on housing components or support frames made of aluminum or aluminum alloys.

[0013] In another variant, a mixture of two or more getter materials is applied to the surface of the component during laser material deposition. In this variant, the powder introduced into the welding fixture is not a single getter material, but rather a powder mixture of several getter materials. This allows for optimized getter surfaces to be created for a wide variety of different contaminants or HIO products.

[0014] In a further development of this variant, the composition of the mixture of getter materials deposited during laser cladding is changed depending on a position on the surface. In this case, the powder composition during laser cladding is changed depending on the position on the surface in order to specifically address or combat various contaminations or contamination effects - depending on the type and location of their occurrence. For example, a different mixture of getter materials can be used in sub-areas of the surface that are close to an optical system, such as a mirror, than in sub-areas that are farther away from the optical system and that are located, for example, in the area of ​​the beam path between two optical systems.

[0015] In a further variant, the at least one getter material is only applied to at least one predefined partial area of ​​the surface during laser material deposition. In this case, the getter material is only applied to selected partial areas of the component's surface and other partial areas are left out, i.e. no getter material is applied to these. The predefined partial area of ​​the surface to which the getter material is applied can, for example, be an optically close partial area. Partial areas that are not relevant with regard to HIO, e.g. on the back of the component, on hidden interface surfaces, etc. can be specifically left out, i.e. the application of the getter material can be omitted in these partial areas.

[0016] In another variant, the at least one getter material applied to the surface is a metal, particularly a precious metal. As described above, the electroplating of getter materials for large components requires very large bath volumes, which results in very high costs, especially for the deposition of precious metals. The costs of applying the getter material(s) by laser deposition are significantly lower in comparison.

[0017] In another variant, the getter material is selected from the group comprising: Ru, Rh, Ir, Pd, Pt, Ni, NiP, and combinations thereof. As described above, not all getter materials are equally suitable for binding a specific HIO product. It is therefore advantageous to combine several getter materials on one and the same surface (possibly in different areas), which is particularly easily achieved when applying the getter materials using laser cladding by using a powder mixture (see above).

[0018] In another variant, laser cladding is performed using a laser beam with a wavelength in the visible wavelength range, i.e., wavelengths between 400 nm and 780 nm. In principle, laser cladding can also be performed using other laser wavelengths, e.g., in the IR wavelength range. The use of a laser wavelength in the visible wavelength range, e.g., in the green wavelength range between 500 nm and 560 nm, has proven particularly advantageous when the getter materials are precious metals, since the absorption of precious metals is greater in this wavelength range than in the IR wavelength range.

[0019] In another variant, laser cladding is performed during a machining process for producing the component. The machining process can, for example, be a material-removing process in which material is removed from the component, e.g., a milling process on a component in the form of a supporting structure or a supporting frame made of aluminum. In this variant, for example, the at least one getter material can be applied by laser cladding in a surface area where material was removed by the milling process.

[0020] The invention also relates to a lithography system, in particular an EUV lithography system, comprising: at least one component having a surface to which at least one getter material is applied by laser deposition welding. The component can be, for example, a structural component, e.g., in the form of a support frame, a housing component, or any other component of the lithography system. The getter material is deposited onto the surface using the method described above.

[0021] 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 of the drawing, which illustrate details essential to the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention. drawing

[0022] Examples of embodiments are shown in the schematic drawing and are explained in the following description. Fig. 1 schematically shows in meridional section a projection exposure system for EUV projection lithography, Fig. 2 a schematic representation of steps of a deposition process of HIO products on a surface of a mirror of the projection exposure apparatus of Fig. 1, and Fig. 3 a schematic representation of a surface of a component during laser deposition welding of getter materials.

[0023] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0024] In the following, with reference to Fig. 1 describes, by way of example, 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 limiting.

[0025] One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optics 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 illumination system. In this case, the illumination system does not include the light source 3.

[0026] A reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced, in particular in a scanning direction, via a reticle displacement drive 9.

[0027] In Fig. 1 shows a Cartesian xyz coordinate system for explanation. The x-direction is perpendicular to the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scanning direction is in the Fig. 1 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0028] The projection exposure system 1 comprises a projection system 10. The projection system 10 is used to image the object field 5 into an image field 11 in an image plane 12. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular along the y-direction, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0029] The radiation source 3 is an EUV radiation source. The radiation source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation has, in particular, a wavelength in the range between 5 nm and 30 nm. The 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. The radiation source 3 can be a free-electron laser (FEL).

[0030] 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 hyperboloidal reflection surfaces. The at least one reflection surface of the collector mirror 17 can be exposed to the illumination radiation 16 at grazing incidence (Gl), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector mirror 17 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0031] 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.

[0032] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. The first facet mirror 20 comprises a plurality of individual first facets 21, which are also referred to below as field facets. Of these facets 21, Fig. 1 shows only a few examples. A second facet mirror 22 is arranged downstream of the first facet mirror 20 in the beam path of the illumination optics 4. The second facet mirror 22 comprises a plurality of second facets 23.

[0033] The illumination optics 4 thus form a double-faceted system. This basic principle is also referred to as a fly's-eye integrator. With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror, or actually the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0034] 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.

[0035] In the Fig. In the example shown in Figure 1, the projection system 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection system 10 is a doubly obscured optical system. The projection optical system 10 has an image-side numerical aperture that is greater than 0.4 or 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0036] The mirrors Mi, just like the mirrors of the illumination optics 4, can have a highly reflective coating for the illumination radiation 16.

[0037] Fig. 2 shows a detail of the projection exposure system 1 of Fig. 1 with one of the mirrors Mi of the projection optics 10 and with a mechanical component 25 that is arranged near the mirror Mi. The mechanical component 25 can be, for example, an actuator, a sensor, a support and / or holding structure, a housing part, etc. A surface 26 of the component 25 is located near the illumination radiation 16 that impinges on the mirror Mi. Hydrogen-volatile contaminants 27 or HIO-forming materials, which can be, for example, phosphorus compounds, silicon compounds, zinc compounds, etc., are deposited on the surface 26 of the component. The hydrogen-volatile contaminants 27 can be deposited on the mirror Mi and form a contamination layer 28 on the surface of the mirror Mi, which leads to a transmission loss of the mirror Mi.

[0038] The deposition of the contamination layer 28 on the mirror Mi can be carried out in four steps (see also Fig. 2): In a first step, the illumination radiation 16 reacts with molecular hydrogen H2, which is present in the environment of the mirror Mi or in the entire projection optics 10, to form hydrogen ions H + or to hydrogen radicals H*, ie a hydrogen plasma is formed. In a second step, the hydrogen plasma, ie H + or H*, with the hydrogen-volatile contaminants 27 to form a volatile compound, typically a volatile hydride, which in Fig. 2 is referred to as the HIO product. In a third step, the HIO product moves from the surface 26 of the component 25 to the surface of the mirror Mi. In a fourth step, the contamination layer 28 is formed there by the HIO product reacting with the material of a cover layer on the surface of the mirror Mi to form a low-volatility compound.

[0039] The formation of the contamination layer 28 on the mirror Mi or on all mirrors Mi (i = 1, ..., 6) of the projection optics 10 as well as on the optical elements 19, 20, 22 of the illumination optics 4 during operation of the projection exposure system 1 leads to a loss of transmission of the projection exposure system 1.

[0040] In order to reduce this transmission loss of the projection exposure system 1 and ideally to avoid it as much as possible, the surfaces of components in the vicinity of the mirrors Mi or the optical elements 19, 20, 22 can be provided with getter materials to which the HIO-forming materials are deposited so that they do not reach the surfaces of the mirrors Mi or the optical elements 19, 20, 22.

[0041] In Fig. 3 shows an example of a detail of such a component 29, which has a flat surface 30 in the example shown. The component 29 is a frame structure, which consists of aluminum at least on its surface 30. In Fig. Figure 3 illustrates the application of two getter materials 31, 32 to the surface 30 of the component 29 by laser cladding. In the example shown, during laser cladding, a laser beam 33 is directed onto the surface 30 of the component 29 and focused there, locally heating and melting the aluminum material of the surface 30. At the same time, the two getter materials 31, 32 are sprayed in the form of fine powder onto the surface 30 of the component 29, or more precisely, onto the molten pool, from a nozzle 34 through which the laser beam 33 also passes. For spraying, the getter materials 31, 32 are guided through an annular gap formed in the nozzle 34, which surrounds the opening through which the laser beam 33 passes.

[0042] The getter materials 31, 32 melt in the molten bath and combine with the molten aluminum material, which forms the base material of the component 29, forming a welded bead 35. For the formation of the weld bead 35, in the example shown, the nozzle 34 is moved in a feed direction over the surface 30, as in Fig. 3 is indicated by an arrow.

[0043] In the example shown, the two getter materials 31 and 32 are each a precious metal, more specifically Pt and Ru. However, other getter materials can also be used, for example, Rh, Ir, Pd, Ni, NiP, etc.

[0044] In the example shown, the laser beam 33 has a laser wavelength λ Lwhich lies in the visible wavelength range, more precisely in the green wavelength range. This is advantageous because the getter materials 31, 32 in the form of precious metals have a high absorption in this wavelength range and are therefore easier to melt than when using a laser wavelength λ L in the IR wavelength range.

[0045] The two getter materials 31, 32 are applied to the surface 30 of the component 29 in the form of a powder mixture containing Pt and Ru powder grains. The combined application of two or more getter materials 31, 32, ... in the form of a mixture to the surface 30 is advantageous for addressing different HIO products and binding them to the surface 30. It is understood that, alternatively, a single getter material can also be applied to the surface 30 of the component 29 by laser deposition welding.

[0046] In the example shown, the composition of the mixture of getter materials 31, 32 deposited during laser cladding is locally modified or varied depending on a position P on the surface 30 in order to address or bind specific HIO products according to their location. A mixing device can be used to vary the composition, which enables the provision of a powder mixture with the desired mixing ratio of the getter materials 31, 32.

[0047] In the example shown, the two getter materials 31, 32 are applied only in a predefined partial area T1 of the surface 30. In the Fig. 3, the end of the welding bead 35 forms the edge of the predefined partial area T1, ie on a Fig.3 No getter materials 31, 32 are applied to the partial area T2 located to the right of the weld bead 35. The predefined partial area T1 is located near an optical system, i.e., near one of the mirrors Mi or one of the optical elements 19, 20, 22. The partial area T2, to which no getter material 31 is applied, may, for example, be a partial area that is shielded by another component, so that the application of getter materials 31, 32 there is not advisable.

[0048] The laser cladding process described above can be performed on a component after its manufacture. However, it is also possible to combine laser cladding with a machining or manufacturing step during the component's production. For example, a milling process in the manufacture of an aluminum support structure can be directly combined with a laser cladding process.

Claims

[1] Method for applying at least one getter material (31, 32) to a surface (30) of a component (29) for a lithography system, in particular for an EUV lithography system (1), comprising: Applying the at least one getter material (31, 32) to the surface (30) of the component (29) by laser deposition welding. [2] Method according to claim 1, wherein the component (29) is formed at least on the surface (30) from stainless steel, from aluminum or from an aluminum alloy. [3] Method according to one of the preceding claims, in which a mixture of two or more getter materials (31, 32) is applied to the surface (30) of the component (29) during laser deposition welding. [4] Method according to claim 3, wherein a composition of the mixture of the getter materials (31, 32) deposited during laser deposition welding is changed depending on a position (P) on the surface (30). [5] Method according to one of the preceding claims, in which, during laser deposition welding, the at least one getter material (31, 32) is applied only in at least one predefined partial area (T1) of the surface (30). [6] Method according to one of the preceding claims, wherein the at least one getter material is a metal, in particular a noble metal. [7] A method according to any one of the preceding claims, wherein the getter material is selected from the group comprising: Ru, Rh, Ir, Pd, Pt, Ni, NiP and combinations thereof. [8] Method according to one of the preceding claims, in which the laser deposition welding is carried out with a laser beam (33) whose laser wavelength (λ L ) is in the visible wavelength range. [9] Method according to one of the preceding claims, in which the laser deposition welding is carried out during a machining process for producing the component (29). [10] Lithography system, in particular EUV lithography system (1), comprising: at least one component (29) having a surface (30) to which at least one getter material (31, 32) is applied by laser deposition welding.

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