Method for atomic layer processing with high lateral resolution

Abstract

The invention relates to a method for atomic layer processing of a surface (25a) of an optical element for lithography, in particular for EUV lithography, comprising: atomic layer processing of the surface (25a) by means of a processing head (26). During atomic layer processing, the surface (25a) is exposed to at least one gas (29) which exits from an outlet opening (28) of a micronozzle (27) of the processing head (26), which has an opening diameter (d) of less than 900 µm. In this way, a high lateral resolution can be achieved during atomic layer processing.

Description

Background of the invention

[0001] The invention relates to a method for atomic layer processing of a surface of an optical element for lithography, in particular for EUV lithography, comprising: atomic layer processing of the surface by means of a processing head.

[0002] The processing, especially the coating, of surfaces with high lateral resolution is a challenge in many applications in the field of optics for lithography, especially for EUV lithography. Examples of such applications include the application of multilayer coatings on MEMS mirrors or on collectors with diffraction gratings, the application or repair of absorber patterns on lithography masks / reticles, and coatings to protect surfaces from silicon etching, e.g., on the sidewalls of EUV mirrors. All of these applications have in common that the application of the coatings should be controlled at small dimensions (typical layer thickness resolution of approximately 2 monolayers, i.e., approximately 0.2 nm, and typical spatial resolution on the order of 1 µm). 2 up to a few µm 2 ).

[0003] The current processes used for this purpose essentially rely on apertures that must be designed, positioned, and manufactured with great precision. The risk of diffusion of specific elements (e.g., Mo, Si, etc.) from the surface or from active Bragg reflector coatings to undesired areas, which can lead to surface roughening, is always present.

[0004] EP3933882A1 describes a device and a method for atomic layer processing of an optical surface of an optical element preferably designed to reflect EUV radiation. The term "atomic layer processing" encompasses atomic layer deposition (ALD) and atomic layer etching (ALE). The device comprises a processing head for atomic layer processing of a curved optical surface, which may have a front end with a width on the order of 5 mm.

[0005] However, with the device described in EP3933882A1, a lateral resolution in the order of magnitude of micrometers cannot be achieved. Object of the invention

[0006] The object of the invention is to enable the atomic layer processing of an optical element for lithography, in particular for EUV lithography, with a high lateral resolution. Subject of the invention

[0007] This problem is solved by a method of the type mentioned above, in which the surface is exposed to a gas during atomic layer processing, which gas emerges from an outlet opening of a micro nozzle of the processing head, which has an opening diameter of less than 900 µm.

[0008] US2022 / 0307133A1, the contents of which are incorporated in its entirety by reference into this application, describes an atomic layer processing printer having a processing head configured for the deposition of material, etching, and / or cleaning on an atomic scale within a selected region. The processing head enables atomic layer processing or atomic layer deposition on a microscale, i.e., with a lateral resolution in the micrometer range. For this purpose, the processing head has at least one exit aperture with an aperture diameter of less than 900 µm. The aperture diameter of the exit aperture can, for example, be between 0.005 µm and 850 µm. The lateral resolution during atomic layer processing depends on the diameter of the exit aperture and the distance between the surface to be processed or the sample and the exit aperture; see also Table 1 of US2022 / 0307133A1.For example, with an exit aperture diameter of approximately 8 µm, a lateral resolution of approximately 10 µm can be achieved in atomic layer processing.

[0009] The processing head is moved at a short distance relative to the surface to be processed. The surface to be processed can be flat or curved and have a complex three-dimensional geometry. For example, the surface can have a relatively high surface roughness, be wavy, etc. The processing head or atomic layer processing printer described above is distributed by Atlant 3D Nanosysteme, see their website "https: / / www.atlant3d.com / technology." As stated there, multilayer patterns with a size of approximately 1 µm can be created using atomic layer deposition. 2with a lateral (x,y) linewidth resolution of approximately 1 µm in the x-direction and approximately 1 µm in the y-direction as well as with an individual resolution of the layer thickness in the vertical direction (z-direction) of approximately 0.2 nm, which corresponds to approximately two atomic monolayers.

[0010] The inventors have recognized that with the aid of the processing head described in US2022 / 0307133A1 or the corresponding method, atomic layer processing with high lateral resolution can also be carried out in a simple manner on optical elements for lithography, especially for EUV lithography.

[0011] In one variant, atomic layer processing involves atomic layer deposition, in which material is deposited on the surface in at least one atomic layer deposition step. Atomic layer deposition can involve the conformal deposition of two- or three-dimensional layers or structures. Atomic layer deposition with the high lateral resolution described above can, for example, be used to apply a multilayer coating for reflecting EUV radiation to MEMS mirrors or MEMS mirror modules, which are used as facet elements of facet mirrors in an illumination system of an EUV lithography system. A conformal, EUV radiation-reflecting coating can also be applied to a collector mirror of an EUV lithography system, which is typically equipped with a diffraction grating. The repair of local defects on masks or mask structures, as well as protective layers, e.g.on the side surfaces of EUV mirrors, is possible due to the high lateral resolution. The atomic layer deposition described here can also be used to correct the local layer thickness of top layers of multilayer coatings.

[0012] In an atomic layer deposition step, two or more self-terminating surface reactions are carried out cyclically. Two or more precursors or reactants are used for atomic layer deposition, which are selected depending on the material to be deposited.

[0013] In one variant, the material deposited on the surface during the atomic layer deposition step is selected from the group comprising: Ru, Si, Mo, C, Cr, Ni, P, Rh, Pd, Pt, Zr, Ti, Nb, Cu, and Ce. For the possibilities for atomic layer deposition of specific chemical elements, please refer to the database of ALD processes available at "https: / / www.atomiclimits.com / alddatabase / ".

[0014] Ru, for example, can be deposited by alternately exposing the surface to a metal-organic precursor (e.g., Ru(ipmp)(chd)) and O2 at a temperature of approximately 220°C, see the article “Low Temperature Atomic Layer Deposition of Ruthenium Thin Films Using Isopropylmethylbenzene-Cyclohexadiene-Ruthenium and O2”, T.-K. Eom et al., Electrochem. Solid-State Lett. 12 (2009) D85. The metal-organic precursor is Ru(ipmp)(chd), i.e. (η 6 -1-isopropyl-4-methylbenzene) (η 4-cyclohexa-1,3-diene)ruthenium(0) (C 16 H 22 Ru). The use of Ru(chd)2, ie Ru(η 5 -cycloheptadienyl)2 and O2 at temperatures between approximately 200°C and approximately 300°C is possible, see the article "Atomic layer deposition of a ruthenium thin film using a precursor with enhanced reactivity", J.M. Hwang et al., J. Mater. Chem. C, 9 (2021) 3820-3825.

[0015] It is also possible to deposit Ru using Ru(CO)2(mhdk)2 as a reactant with H2 as a co-reactant at a temperature of 250°C, see the article “Plasma-free atomic layer deposition of Ru thin films using H2 molecules as a nonoxidizing reactant”, S.-Y. Lee et al., Journal of Vacuum Science & Technology A 34, (2016) 031509. Ru(CO)2(mhdk)2 is dicarbonyl-bis(5-methyl-2,4-hexanediketonato) Ru(II) (C 16 H 22O6Ru). Ru(CO)2(mhdk)2 can also be used as a reactant for the deposition of Ru with NH3 plasma at temperatures from 175°C to 310°C, see the article "Atomic Layer Deposition of Ru Thin Films Using a New Beta-Diketonate Ru Precursor and NH3 Plasma as a Reactant", J.-H. Jung et al., Journal of Nanoscience and Nanotechnology, Vol. 15, No. 11, November 2015, pp. 8472-8477(6).

[0016] The deposition of Si by atomic layer deposition can also be achieved in different ways. For example, deposition can be carried out using disilane (Si2H6) in an electron-assisted ALD process at approximately 20°C, see the article "Electron-enhanced atomic layer deposition of silicon thin films at room temperature", J.K. Sprenger et al., Journal of Vacuum Science & Technology A 36, (2018) 01A118. To deposit Si, the surface can also be exposed to Si2H6 alternating with SiCl4 at temperatures between 355°C and 385°C, see the article "Self-limiting atomic-layer deposition of Si on SiO2 by alternate supply of Si2H6 and SiCl4", S. Yokoyama et al., Appl. Phys. Lett. 70 (2001) 617. The deposition of Si can also be achieved by exposing the surface alternately to Si2Cl6 and atomic hydrogen at temperatures below 500°C, e.g. at 400°C, cf.den Artikel „Atomic layer epitaxy of Si on Ge(100) using Si2Cl6 and atomic hydrogen“, D. D. Koleske et al., J. Appl. Phys. 76, (1994) 1615.

[0017] For the deposition of Mo in the atomic layer deposition step, MoF6 and SiH6, for example, can be used as reactants; see the article "Molybdenum Atomic Layer Deposition Using MoF6 and Si2H6 as the Reactants," D. Seghete et al., Chem. Mater., 23, (2011), pages 1668-1678. Mo deposition is also possible using Mo(CO)6 and a hydrogen plasma at a temperature of approximately 300°C; see the article "Electrical Properties of Molybdenum Metal Deposited by Plasma Enhanced - Atomic Layer Deposition of Variation Condition," T. Lim et al., Korean J. of Materials Research, Vol. 29, No. 11 (2019), pages 715-719. It is also possible to deposit Mo using MoCl5 and Zn as reducing co-reactant at temperatures between 400°C and 500°C, see the article “Deposition of molybdenum thin films by an alternate supply of MoCl5 and Zn”, M. Juppo et al., Journal of Vacuum Science & Technology A 16, (1998) 2845-2850.

[0018] The deposition of C can be carried out, for example, using CCl3 and atomic hydrogen, see the article “Novel method for chemical vapor deposition and atomic layer epitaxy using radical chemistry”, TI Hukka et al., Thin Solid Films, Vol. 225, Issues 1-2 (1993), pages 212-218, or using CF x and atomic hydrogen, see the article “Self-limiting diamond growth from alternating CF x and H fluxes“, SF Komarov et al., Diamond and Related Materials, Vol. 7, Issue 8 (1998), pages 1087-1094, each at temperatures between approximately 200°C and 300°C.

[0019] Cr can also be deposited using metal complexes, see the article “Volatile and Thermally Stable Mid to Late Transition Metal Complexes Containing α-Imino Alkoxide Ligands, a New Strongly Reducing Coreagent, and Thermal Atomic Layer Deposition of Ni, Co, Fe, and Cr Metal Films”, LC Kalutarage et al., J. Am. Chem. Soc. 135, 34 (2013), pages 12588-12591.

[0020] Si and Mo are materials typically used as layer materials in multilayer coatings designed to reflect EUV radiation at an electromagnetic wavelength of approximately 13.5 nm, acting as Bragg reflectors. Ru can be used as a top layer in such multilayer coatings and other coatings. Depending on the wavelength of the radiation to be reflected by the coating, other materials or material combinations can also be used in a multilayer coating that acts like a Bragg reflector, e.g. Cr or B4C, as described, for example, in US2011 / 0080573 A1, or material combinations such as La / B4C or Cr / Sc, see the presentation "Adaptation of the reflectance of Bragg mirrors to wide source spectra", R. Meisels and F. Kuchar, Institute of Physics, Montanuniversität Leoben, Austria, "https: / / www.euvlitho.com / 2019 / P57.pdf".

[0021] In another variant, a layer of the material is deposited on the surface using atomic layer deposition. As described above, the material can be deposited locally using atomic layer deposition, for example, to correct defects in masks or the like. However, it is also possible to apply the material to the surface in the form of a continuous layer. The layer can be, for example, a layer of a multilayer coating for reflecting EUV radiation, e.g., a layer of Si or Mo, or a cover layer of Ru.

[0022] In a further development of this variant, the layer is deposited in at least one macrocycle, which comprises at least one atomic layer deposition step and at least one etching-back step for partially etching back the layer, wherein the etching-back step is preferably carried out as an atomic layer etching step. The term macrocycle refers to the two method steps described here, which are carried out one after the other, i.e. the deposition of material by means of atomic layer deposition in at least a first step, which is referred to as the atomic layer deposition step, and the subsequent partial etching back in a second step, which is referred to as the etching back step. The deposition of the layer takes place in one or more macrocycles, in which the material of the layer deposited in the selective, conformal 2D / 3D atomic layer deposition is partially etched back by selective 2D / 3D atomic layer etching. In this way, the deposited layer orTheir surface can be smoothed. Repeated application of the macrocycles can also further smooth the interfaces between adjacent layers of a multilayer coating. The macrocycles can also be used to deposit a cover layer on an optical element, as described, for example, in WO2022 / 263061A1.

[0023] In another variant, a plurality of layers are applied to the surface during atomic layer deposition, forming a coating for reflecting EUV radiation. As described above, alternating layers of Si and Mo can be applied to form a Bragg reflector. The coating can also comprise additional functional layers, such as a cover layer of Ru. During atomic layer deposition of the respective layers, the partial etching back described above can be used, in particular, to smooth the interfaces between the individual layers. Smoothing by partial etching back can be carried out, in particular, on the Si layers.

[0024] In a further variant, a layer, particularly in the form of a protective layer, is deposited on a surface of the optical element that forms a side surface of a substrate of the optical element. As described above, it is also possible for a protective layer, for example made of Ru, to be deposited on a side surface of the substrate that is not covered by the reflective coating. The protective layer can serve, for example, to protect the surface from etching by a hydrogen plasma.

[0025] The atomic layer etching process—like the atomic layer deposition process—can be performed thermally, plasma-assisted, or electron beam-assisted. Plasma-assisted etching, in particular, allows process temperatures to be reduced to room temperature, if necessary. The atomic layer etching process—like the atomic layer deposition process—can be performed at atmospheric pressure using a suitable device that incorporates the processing head described above. "Dry" chemistry can be used in atomic layer deposition to deposit Mo (e.g., plasma-assisted), Si (e.g., plasma-assisted, electron beam-assisted, etc.), or other materials.

[0026] In another variant, the atomic layer processing comprises at least one cleaning step for cleaning the surface by atomic layer etching.

[0027] It is not mandatory that atomic layer etching be performed to partially etch back deposited material; rather, atomic layer etching can also be used to perform etch-based (pre-)cleaning to remove contaminants such as Sn, C, etc. using "dry" etch chemistry that generates volatile etch products such as SnH4, CH4, etc. In the intermittently performed back etch steps, "dry" chemistry can also be used to generate volatile etch products such as SiH4, etc.

[0028] As described above, a material deposited during atomic layer deposition can be partially etched back by an etchback step, particularly an atomic layer etch. The latter requires the use of an atomic layer etching process suitable for etching back the respective material. For information on the possibilities for atomic layer etching of specific chemical elements, please refer to the ALE process database, available at "https: / / www.atomiclimits.com / aledatabase / ."

[0029] For atomic layer etching of silicon, for example, O2, HF, and Al(CH3)3 can be used as reactants at temperatures between approximately 225°C and 290°C, see the article “Thermal Atomic Layer Etching of Silicon Using O2, HF, and Al(CH3)3 as the Reactants,” AI Abdulagatov et al., Chem. Mater. 30, 23 (2018), pages 8465-8475.

[0030] For the etching back or atomic layer etching of Ru, for example, ozone gas can be used at temperatures between 25°C and 60°C, as described in the article "Etching technique for ruthenium with a high etch rate and high selectivity using ozone gas", M. Nakahara, J. Vac. Sc. Technol. B:19 (2001) 2133. The process described therein does not involve atomic layer etching, but is indicative of the possibility of performing etching back by atomic layer etching. The etching back of Ru is also described in the article "Etching of ruthenium coatings in O2- and Cl2-containing plasmas" by CC Hsu et al., J. Vac. Sc. Technol. A, 24 (2006), pages 1-8.

[0031] For Mo back etching, inductively coupled O2, C12, or Ar plasmas at temperatures between 40°C and 60°C can also be used; see the article "Dry etching characteristics of Mo and Al2O3 films in O2 / Cl2 / Ar inductively coupled plasmas," KH Kwon et al., Thin Solid Films, 552 (2014), pages 105-110. The process described therein does not involve atomic layer etching, but is indicative or serves as a prediction for the possibility of performing back etching by atomic layer etching.

[0032] The etching back of C by atomic layer etching can be carried out, for example, in the manner described in US 4,756,794, ie by a sequence in which the carbon material is repeatedly exposed to NO2 and bombarded with a mixture of noble gas ions and hydrogen ions.

[0033] The process temperatures at which a respective atomic layer deposition step and an atomic layer etching step, for example in the form of an etch-back step, are performed can differ from one another. The difference in process temperatures requires rapid heating and cooling of the optical element, more precisely its surface, which can be achieved, for example, using so-called "rapid thermal processing." It is also possible to preheat the gas supply lines integrated into the processing head with the micronozzle or microinjector in order to achieve the target temperature at the location of the object to be processed for the respective processing operation (cleaning, deposition, etching, etc.).Alternatively, the rapid and local heating of the surface of the optical element can also be achieved by integrating a micro-laser into the processing head with the micro-injector, which is precisely aligned with respect to the exit direction of the gas from the processing head and is arranged sufficiently close to the nozzle that forms the gas outlet in order to generate the optimal temperature on the surface of the optical element or the substrate of the optical element.

[0034] 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

[0035] 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 an atomic layer processing printer for atomic layer processing of a surface of an optical element, which has a processing head with a micro nozzle, and Fig. 3 a schematic representation of a reflective coating produced with the atomic layer processing printer of Fig. 2 was separated.

[0036] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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 (GI), 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.

[0044] 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.

[0045] 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 flat 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The mirrors Mi, just like the mirrors of the illumination optics 4, can have a highly reflective coating for the illumination radiation 16.

[0050] Fig. Figure 2 shows a device in the form of an atomic layer processing printer 24, which in the example shown serves to deposit a highly reflective coating on a surface 25a of a substrate 25. The atomic layer processing printer 24 is designed as shown in US2022 / 0307133A1 and has a processing head 26 with a micronozzle 27, which has an outlet opening 28 with an opening diameter d of less than 900 µm. The opening diameter d in the example shown is approximately 2 µm. A gas 29 emerges from the micronozzle 27, which serves as a reactant or co-reactant in the atomic layer processing of the surface 25a. As shown in Fig. 2, the substrate 25 is held on a holding plate 30 of the atomic layer processing printer 24 during atomic layer processing.

[0051] During atomic layer processing, the processing head 26 is arranged at a small distance from the surface 25a, which is in the order of magnitude of approximately 2 µm. In this way, a lateral resolution can be achieved during atomic layer processing which is in the order of magnitude of approximately 1 µm in the x-direction and approximately 1 µm in the y-direction of a Fig. 2. For processing at different locations on the surface 25a, the substrate 25 can be moved, or more precisely, displaced, relative to the processing head 26. The resolution in the Z direction, ie, perpendicular to the surface 25a, is typically on the order of a few nanometers, e.g., 2 nanometers.

[0052] In the Fig. 2, the reflective coating is applied to the surface 25a of a substrate 25 of an optical element in the form of a micromirror module of a facet 21 of the first facet mirror 20 of the illumination optics 4 of Fig. 1 separated. Fig. 3 shows a cross-section through the uppermost layers of this reflective coating 31. It is understood that the atomic layer deposition of the reflective coating 31 can also be carried out on another mirror of the EUV lithography system 1 or on another reflective optical element, for example on a photomask.

[0053] In atomic layer deposition, the Fig. 3, the reflective coating 31 is applied in the form of a multilayer coating or layer stack. The layer stack typically comprises between 50 and 100 double layers 32, each double layer 32 comprising a first layer 33 consisting of a first layer material and a second layer 33' consisting of a second layer material. In the case shown, the first layer material is silicon, while the second layer material is molybdenum, but other materials can also be used as layer materials, for example La and B4C or Cr and Sc. In the case shown of a reflective coating 31 in the form of a layer stack, the reflection of the EUV radiation is based on interference effects. Alternatively, the reflective coating 31 can also have only a few layers and serve to reflect EUV radiation 16 at grazing incidence.

[0054] The reflective coating 31 also has a cover layer 34, which in the example shown is made of ruthenium and serves to protect the underlying layers 33, 33' from oxidation. The cover layer 34 is also applied by atomic layer deposition in the example shown.

[0055] During the application of the reflective multilayer coating 31, the Mo layers 33' are deposited by atomic layer deposition, performing several self-terminating atomic layer deposition steps one after the other until the desired layer thickness is achieved. The atomic layer deposition of Mo can be realized using different reactants or precursors, for example, using MoF6 and Si2H6 as reactants at temperatures of approximately 90-150°C.

[0056] The deposition of each Si layer 33 takes place in at least one macrocycle, which comprises at least one atomic layer deposition step and at least one etch-back step for partially etching back the layer 33. In the example shown, the etch-back step is carried out as an atomic layer etching step. The atomic layer deposition step of Si can, for example, be carried out using disilane (Si2H6) as a reactant in an electron-assisted ALD process for electron-induced hydrogen desorption, which is carried out at room temperature. The etch-back step for partially etching back the Si layer 33 is realized by atomic layer etching, using O2, HF, and Al(CH3)3 as reactants for thermal atomic layer etching at temperatures in the range of approximately 225°C to 290°C. The macrocycles are carried out until the layer 33 has the desired layer thickness.The combination of atomic layer deposition, usually in several atomic layer deposition steps, and a partial etching back in one or more macrocycles makes it possible to realize a smooth interface to a subsequently deposited layer 33' of Mo.

[0057] In order to reach the temperature required for the subsequent atomic layer etching step as quickly as possible after the respective atomic layer deposition step, which is carried out at room temperature, which in the example shown is more than 225°C, the gas 29 can be preheated in supply lines of the processing head 26 before exiting the micro nozzle 27. Local preheating or heating of the surface 25a of the substrate 25 is also possible, for example by irradiating a laser beam generated by a micro laser onto the area of ​​the substrate 25 to be processed or adjacent to the area of ​​the substrate 25 to be processed.

[0058] As described above, in the example shown the cover layer 34 made of Ru is also deposited by atomic layer deposition using the method described in Fig. 2, using Ru(chd)2 and O2 as reactants at temperatures between approximately 200°C and 300°C.

[0059] The atomic layer processing may also include a cleaning step for cleaning the surface 25a or the surfaces of a respective deposited layer 33, 33' before a further layer 33, 33' is deposited thereon.

[0060] The deposition of other materials, e.g., Cr or C, can also be performed using the atomic layer processing printer 24 to deposit reflective coatings designed to reflect radiation at wavelengths other than 13.5 nm. The reflective coating 31 described here can also be applied to a surface 25a that is structured, as is the case with the collector mirror 17 described above.

[0061] It is understood that local atomic layer processing using the atomic layer processing printer 24 can also be used for other purposes, for example, to correct local defects in structures on a mask or to apply structures to a mask for EUV lithography. Local defects can also be corrected by atomic layer processing on protective layers, which are applied, for example, to the side surfaces of optical elements for lithography, or such protective layers can be deposited there. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 3933882A1 [0004, 0005] US 2022 / 0307133A1 [0008, 0010, 0050] US 2011 / 0080573 A1

[0020] WO 2022 / 263061A1

[0022] US 4,756,794

[0032] Zitierte Nicht-Patentliteratur

[0000] T.-K. Eom et al., Electrochem. Solid-State Lett. 12 (2009)

[0014] Atomic layer deposition of a ruthenium thin film using a precursor with enhanced reactivity“, J-M. Hwang et al., J. Mater. Chem. C, 9 (2021) 3820-3825

[0014] Plasma-free atomic layer deposition of Ru thin films using H2 molecules as a nonoxidizing reactant“, S.-Y. Lee et al., Journal of Vacuum Science & Technology A 34, (2016) 031509

[0015] Atomic Layer Deposition of Ru Thin Films Using a New Beta-Diketonate Ru Precursor and NH3 Plasma as a Reactant“, J.-H. Jung et al., Journal of Nanoscience and Nanotechnology, Vol. 15, No. 11, November 2015, pp. 8472-8477(6)

[0015] Electron-enhanced atomic layer deposition of silicon thin films at room temperature“, J.K. Sprenger et al., Journal of Vacuum Science & Technology A 36, (2018) 01A118

[0016] Self-limiting atomic-layer deposition of Si on SiO2 by alternate supply of Si2H6 and SiCl4“, S. Yokoyama et al., Appl. Phys. Lett. 70 (2001) 617

[0016] Atomic layer epitaxy of Si on Ge(100) using Si2Cl6 and atomic hydrogen“, D. D. Koleske et al., J. Appl. Phys. 76, (1994) 1615

[0016] Molybdenum Atomic Layer Deposition Using MoF6 and Si2H6 as the Reactants“, D. Seghete et al., Chem. Mater., 23, (2011), Seiten 1668-1678

[0017] Electrical Properties of Molybdenum Metal Deposited by Plasma Enhanced - Atomic Layer Deposition of Variation Condition", T. Lim et al., Korean J. of Materials Research Vol. 29 No. 11 (2019), Seiten 715-719

[0017] Deposition of molybdenum thin films by an alternate supply of MoCl5 and Zn“, M. Juppo et al., Journal of Vacuum Science & Technology A 16, (1998) 2845-2850

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[0031]

Claims

[1] Method for atomic layer processing of a surface (25a) of an optical element (21) for lithography, in particular for EUV lithography, comprising: Atomic layer processing of the surface (25a) by means of a processing head (26), characterized by that the surface (25a) is exposed during atomic layer processing to at least one gas (29) which emerges from an outlet opening (28) of a micro nozzle (27) of the processing head (26) which has an opening diameter (d) of less than 900 µm. [2] The method of claim 1, wherein the atomic layer processing comprises atomic layer deposition in which material is deposited on the surface (25a) in at least one atomic layer deposition step. [3] The method according to claim 2, wherein the material deposited on the surface (25a) in the atomic layer deposition step is selected from the group comprising: Ru, Si, Mo, C, Cr, Ni, P, Rh, Pd, Pt, Zr, Ti, Nb, Cu, Ce. [4] Method according to claim 2 or 3, wherein during atomic layer deposition at least one layer (33, 33', 34) of the material is deposited onto the surface (25a). [5] Method according to claim 4, wherein the at least one layer (33) is deposited in at least one macrocycle comprising at least one atomic layer deposition step and at least one etching back step for partially etching back the layer (33), wherein the etching back step is preferably carried out as an atomic layer etching step. [6] Method according to claim 4 or 5, wherein during atomic layer deposition a plurality of layers (33, 33', 34) are applied to the surface (25a), which form a coating (31) for reflecting EUV radiation (16). [7] Method according to one of claims 4 or 5, wherein the at least one layer, in particular in the form of a protective layer, is deposited on a surface (25a) of the optical element (21) which forms a side surface of a substrate (25) of the optical element (21). [8] Method according to one of the preceding claims, wherein the atomic layer processing comprises at least one cleaning step for cleaning the surface (25a) by atomic layer etching.

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