Method and apparatus for atomic layer deposition of fluoride layer, optical element and optical arrangement

Abstract

To provide a method and an apparatus for atomic layer deposition of a fluoride layer, an optical element and an optical arrangement.SOLUTION: This invention relates to a method of depositing at least one fluoride layer (2), comprising depositing the fluoride layer (2) on a substrate (3) by photo-assisted atomic layer deposition, ALD, in a multitude of ALD cycles. The method comprises irradiating the fluoride layer (2) with UV / VIS light (10a) in at least some of the multitude of ALD cycles, in particular in all of the ALD cycles, in order to anneal at least one potential crystal defect in the fluoride layer (2). The invention also relates to an apparatus (1) for atomic layer deposition of at least one fluoride layer (2), to an optical element comprising a substrate (3) coated with such a fluoride layer (2), and to an optical arrangement comprising at least one such optical element.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from German Patent Application No. 102024201149.5, filed February 8, 2024, the disclosure of which is hereby incorporated by reference in its entirety into the disclosure of this application.

[0002] The present invention relates to a method for depositing a fluoride layer by atomic layer deposition (ALD), comprising depositing a fluoride layer on a substrate over multiple ALD cycles. The present invention also relates to an apparatus for atomic layer deposition of at least one fluoride layer, comprising an ALD chamber having a holder for a substrate and a gas supply device for supplying a fluorinated active material to the ALD chamber. The present invention further relates to an optical element for reflection and / or transmission of radiation in the VUV wavelength range having a substrate coated with a fluoride layer, and an optical setup for the VUV wavelength range having at least one such optical element. [Background technology]

[0003] In the present application, the VUV wavelength range is understood to mean the wavelength range of electromagnetic radiation between 115 nm and 190 nm. The VUV wavelength range is particularly important for microlithography. For example, radiation in the VUV wavelength range is used in projection exposure apparatus and wafer or mask inspection apparatus, for example.

[0004] In such systems, optical elements with at least one fluoride layer are often used. Highly reflective optical elements for the VUV wavelength range typically have a fluoride layer, for example to protect the underlying metal layer from oxidation, through which the radiation is reflected. For reflective or anti-reflective coatings of optical elements, additional layers of different fluorides or fluorides with optional oxides can be used. However, the high radiation intensities required for wafer or mask inspection and projection exposure systems can cause degradation of the fluoride and the entire optical element, thereby shortening its lifetime.

[0005] DE 102021201477 A1 describes a method for operating an optical system comprising at least one optical element containing a fluoride, the optical system comprising a regenerative radiation system providing electromagnetic regenerative radiation having a UV wavelength for irradiating the optical element and for causing annealing of defects in the fluoride.

[0006] Degradation can also be suppressed using high-density fluoride layers, which can in principle be deposited by physical vapor deposition (PVD), for example by sputtering deposition. Chemical vapor deposition (CVD), in particular atomic layer deposition (ALD), is a particularly promising method for the deposition of fluoride layers, or layers of optical elements in general.

[0007] In atomic layer deposition, several ALD cycles are performed sequentially, each depositing one or more stacks of layers. An ALD cycle includes two or more reaction steps, each of which results in a self-terminating surface reaction. Typically, an ALD cycle involves a first partial reaction with a first precursor in a first reaction step, followed by a second partial reaction with a second precursor, also called a co-reactant, in a second reaction step to reactivate the surface for the first reaction step. A purge step is generally performed between each two reaction steps.

[0008] Atomic layer deposition for the deposition of layers of optical devices has been described in the literature, including the following references:

[0009] US Patent Application Publication No. 2023 / 0123796 describes an optical component made of crystalline calcium fluoride with a conformal coating deposited by atomic layer deposition. DE Patent Publication No. 102018211499 describes a process for producing optical elements for the VUV wavelength range, in which at least two layers are applied to a substrate by atomic layer deposition.

[0010] WO 2021 / 021436 describes an atomic layer deposition method for coating optical lenses with a magnesium fluoride layer, in which a magnesium oxide layer is first formed and then converted into a magnesium fluoride layer.

[0011] International Application No. 2023 / 101862 describes a protective coating for an aluminum mirror. To produce it, an aluminum layer is deposited on a glass substrate by a physical deposition process, first and second fluorine-containing layers, such as MgF2 or AlF3, are deposited on the aluminum layer by a physical deposition process, and a third fluorine-containing layer is deposited on the second fluorine-containing layer by an atomic layer deposition process. Prior to the deposition of the first fluorine-containing layer, a native aluminum oxide layer can be removed from the surface of the aluminum layer by an atomic layer etching process.

[0012] Although thermal ALD processes are generally unattractive due to the elevated temperatures involved in coating optical components, ALD processes, particularly those photoassisted or based on the use of plasma, are promising.

[0013] U.S. Patent No. 7,798,096 describes the use of UV light to assist the deposition of high-k dielectrics using chemical vapor deposition or atomic layer deposition, where UV light is used to excite or ionize process gases and thereby initiate or enhance surface reactions during deposition.

[0014] U.S. Patent Application Publication No. 2005 / 0148206 describes an ALD process in which electromagnetic radiation is supplied to a layer during or after exposure of the layer to a second reactant to destabilize undesired bonds, particularly metal-metal bonds, by excitation and convert them to a desired bond form.

[0015] U.S. Patent Application Publication No. 2017 / 0058401 describes a light-assisted ALD process for metals in which light is used to dissociate precursors. Various wavelengths can be provided to maximize the efficiency of dissociating the precursors.

[0016] The paper "Photo-Assisted ALD: Process Development and Application Perspectives," by V. Miikkulainen, 2017 ECS Trans. 80 49, states that photo-assisted ALD can simplify what is called selective area ALD, and specifically describes a photo-assisted ALD process for metal oxides and metals using D2 lamps.

[0017] The paper "Atomic layer deposition of aluminum fluoride using Al(CH3)3 and SF6 plasma," MFJ Vos et al., Applied Physics Letters 111, 113105 (2017), describes the deposition of dense layers of AlF3 using trimethylaluminum (Al(CH3)3) as a precursor and SF6 as a co-reactant at temperatures between 50 and 300 °C. This paper and its supplementary material report the absorption coefficients of deposited AlF3 layers. The absorption coefficients reported in this paper for the VUV wavelength range are relatively high and increase as the deposition temperature decreases, resulting in poorer optical performance of the deposited AlF3 layers. The paper attributes the relatively large absorption coefficient at a deposition temperature of 50 °C to a higher proportion of sulfur in the environment. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] German Patent Publication No. 102021201477 [Patent Document 2] U.S. Patent Application Publication No. 2023 / 0123796 [Patent Document 3] German Patent Publication No. 102018211499 [Patent Document 4] International Application No. 2021 / 021436 [Patent Document 5] International Application No. 2023 / 101862 [Patent Document 6] U.S. Patent No. 7,798,096 [Patent Document 7] U.S. Patent Application Publication No. 2005 / 0148206 [Patent Document 8] U.S. Patent Application Publication No. 2017 / 0058401 [Non-patent literature]

[0019] [Non-Patent Document 1] “Photo-Assisted ALD: Process Development and Application Perspectives”, V. Miikkulainen, 2017 ECS Trans. 80 49 [Non-patent document 2] “Atomic layer deposition of aluminum fluoride using Al(CH3)3 and SF6 plasma”, MFJ Vos et al., Applied Physics Letters 111, 113105 (2017) Summary of the Invention [Problem to be solved by the invention]

[0020] It is an object of the present invention to define a method and apparatus for atomic layer deposition of fluoride layers with high optical performance, as well as optical elements and optical setups including such optical elements. [Means for solving the problem]

[0021] According to a first aspect, this object is achieved with a method of the kind specified in the introduction, which method comprises the additional step of irradiating the fluoride layer with UV / VIS light in at least some, in particular all, of the ALD cycles in order to anneal at least one latent crystalline defect in the fluoride layer, the fluoride layer typically being a metal fluoride layer.

[0022] The inventors have recognized that a drawback of photo-assisted and plasma-assisted ALD processes is that the deposited fluoride layer is exposed to high-energy photons in the UV and VUV wavelength range during the coating process. This high-energy light typically has the effect of forming defects (e.g., color centers) in the fluoride layer. These defects, especially those occurring in the bulk of the grown layer, adversely affect both the optical performance, i.e., absorption in the useful wavelength range—in this case, the VUV wavelength range—and the lifetime of the optical component. These defects, especially at relatively low deposition temperatures, are the actual cause of the larger extinction coefficients described in the above-cited paper by MFJ Vos.

[0023] To resolve the technical conflict between, on the one hand, the desired low deposition temperature in an ALD process and, on the other hand, solid, defect-free growth, the inventors propose providing additional light to anneal crystalline defects typically or potentially formed during an ALD process, particularly during a photo-assisted or plasma-enhanced ALD process. Irradiation with UV / VIS radiation to anneal crystalline defects typically or potentially formed in the deposition of a fluoride layer can be performed during any ALD cycle, but it is also possible for irradiation to occur only in some of the ALD cycles, e.g., once every 2, 3, 4, ... ALD cycles, provided that irradiation is sufficient to anneal potential crystalline defects in the volume of the fluoride layer.

[0024] In the context of the present application, UV light is understood to mean electromagnetic radiation in the wavelength range of 100 nm to 380 nm. In the context of the present application, VIS light is understood to mean radiation in the wavelength range of 380 nm to 830 nm. In the context of the present application, UV / VIS light is understood to mean radiation in the wavelength range of 100 nm to 380 nm (UV light) and / or 380 nm to 830 nm (VIS light). The UV / VIS wavelength range can be further limited, for example, in the range of 170 nm to 730 nm. Irradiation with UV / VIS light is generally not carried out over the entire UV / VIS wavelength range, but rather in one or more selected spectral regions that are adapted in each case to the crystalline defects to be annealed, in particular defects in the form of color centers, e.g., F-centers. Each spectral region can optionally include only a single wavelength, for example, if the UV / VIS light is generated by a laser source, e.g., an excimer laser.

[0025] Suitable wavelengths can be selected, for example, as described in DE 102021203505 A1, which is incorporated herein by reference in its entirety, which describes depositing a layer of ionically bonded solid material on a substrate by converting a coating material into a gas phase and depositing the gas phase converted coating material on the substrate, wherein the layer is irradiated with UV / VIS light in a first spectral region that at least partially overlaps with the absorption region of at least one (potential) crystalline defect during deposition in order to immediately anneal (potential) crystalline defects formed during deposition of the coating material.

[0026] In one variation of the method according to the invention, a fluoride layer is exposed to a metal precursor in the first reaction step of each ALD cycle, and the fluoride layer is preferably not irradiated with UV / VIS light in the first reaction step to anneal at least one potential crystalline defect. The deposited fluoride layer is typically a metal fluoride layer deposited using a metal precursor. Irradiation with UV / VIS light to anneal potential crystalline defects during the first reaction step is generally not preferred, in part because UV / VIS light can undesirably excite or dissociate the metal precursor, which can adversely affect layer formation.

[0027] In a further development of this variant, the metal precursor is selected from the group including Al(CH3)3, AlCl3, (C2H5)3Al, Mg(thd)2, Mg(EtCp)2, Ca(thd)2, La(thd)2, and LiHMDS. The metal precursor is selected depending on the nature of the fluoride layer deposited in the ALD process. For an AlF3 layer, for example, Al(CH3)3, i.e., trimethylaluminum (TMA), AlCl3, i.e., trichloroaluminum, or (C2H5)3Al, i.e., triethylaluminum, can be used. For an MgF2 layer, for example, Mg(thd)2 or Mg(EtCp)2 can be used, where "thd" is 2,2,6,6-tetramethyl-3,5-heptanedionate and "EtCp" is ethylcyclopentadienyl. The metal precursor used in the case of a CaF2 layer may be, for example, Ca(thd)2, in the case of a LaF3 layer, for example, La(thd)2, and in the case of a LiF layer, for example, LiHMDS, i.e., lithium hexamethyldisilazide.

[0028] In a further variation, the fluoride layer is irradiated with UV / VIS light to anneal at least one potential crystalline defect during and / or after the second reaction step of each ALD cycle in which the fluoride layer is exposed to a reactive fluorine precursor. In this variation, the reactive fluorine precursor is typically generated by exciting a fluorinated active material, which can be excited using a plasma or electromagnetic radiation, i.e., light. The inventors have recognized that irradiation with UV / VIS light is preferably performed in a dedicated bleaching step during or after the second reaction step to anneal at least one potential crystalline defect, also referred to as "bleaching." If bleaching is performed in a dedicated bleaching step, it may be preferable to also expose the fluoride layer to a fluorinated active material during this additional bleaching step.

[0029] In a further development of this variant, the reactive fluorine precursor is generated by plasma generation from a fluorinated active material. The atomic layer deposition process may be carried out, for example, as described in the article by MFJ Vos et al., cited at the beginning and incorporated herein by reference in its entirety. In the ALD process described therein, SF gas is used as the fluorinated active material, from which an inductively coupled plasma is generated in a plasma source, and reactive fluorine precursors or reactive fluorine species, such as F, F, SF, and SF, are used. 5+ Contains ions, F - Similarly, the paper states that for plasma ALD processes, other fluorinated active materials, such as HF or HF pyridine, can also be used.

[0030] In a further variation, the reactive fluorine precursor is generated from the fluorinated active material by photodissociation. In this variation, the fluorinated active material is irradiated with light, typically UV / VIS light having at least one wavelength whose energy is at least as great as the dissociation energy of the fluorinated active material. The light source used for photodissociation can be, for example, a deuterium lamp that emits light substantially continuously in the wavelength range of about 115 nm to about 800 nm.

[0031] In a further embodiment, the fluorinated active substance is selected from the group consisting of SF, NF, HF, HF-pyridine, F, NHF, CF, CHF, TiF, WF, MoF, and TaF. As mentioned above, the fluorinated active substance, typically in the gas phase, can be activated, i.e., converted into a reactive fluorine precursor, by photodissociation or by plasma formation, so that the second (partial) step of the reaction in each ALD cycle can proceed at the surface of the fluoride layer. As mentioned above, instead of or in addition to irradiation in the second reaction step, it may be advantageous if irradiation with UV / VIS light is performed in a dedicated bleaching step in which the fluoride layer is exposed to the fluorinated active substance without activating the fluoride layer.

[0032] In a further variation, the method includes irradiating the fluoride layer with light in a third spectral region for photodissociation of the fluorinated active material, the third spectral region being in a useful wavelength region of the optical element formed in the deposition of the fluoride layer, particularly in the VUV wavelength range.

[0033] In this variant, the fluorinated active substance is photodissociated by irradiating the fluoride layer with light in a third spectral region. It has been found to be advantageous if the third spectral region is in the useful wavelength range of the optical element, for example, in the VUV wavelength range. The third spectral region may optionally include only one wavelength, but can also be a broader spectral region. Again, the light source used for photodissociation may be a deuterium lamp, with wavelengths outside the useful wavelength range, for example, wavelengths above 190 nm, being blocked by optical filtering. An advantage of using a third spectral region in the useful wavelength range of the optical element is that in this case, only weak energy input, if any, is made to the substrate of the optical element during deposition of the fluoride layer.

[0034] In a further variant, the fluoride layer is irradiated with a first spectral region to anneal at least one potential crystal defect with UV / VIS light, and preferably with light in a second spectral region to mobilize atoms at its surface. As described above and in DE 102021203505, the appropriate wavelength for the first spectral region or for annealing the potential crystal defects depends on the energy absorption of the crystal defects or the anion-cation distance in the fluoride layer. For example, for an AlF3 layer, the first spectral region may be approximately 170 nm to 190 nm, and for an MgF2 or LaF3 layer, the center wavelength may be at or near 260 nm. The fluoride layer may be irradiated with UV / VIS light in the second spectral region to mobilize atoms at its surface, as described in DE 102021203505. The second spectral region may for example lie between 75% and 100%, preferably between 80% and 95% of the band gap energy of the fluoride layer. The second spectral range may in particular lie between 115 nm and 122 nm.

[0035] In a development of this variant, the first spectral range lies at wavelengths above 190 nm. Annealing of crystalline defects using UV / VIS light having a first spectral range at wavelengths above 190 nm has proven to be favorable.

[0036] In one development of this variant, at least two fluoride layers with different metal components are deposited on the substrate, and the first spectral region of the fluoride layers during irradiation is adapted to the respective metal components. As mentioned above, the first spectral region for annealing the at least one potential crystal defect can be selected or adapted depending on the metal component of the fluoride layer, in this case a metal fluoride layer. It will be appreciated that it is also possible to deposit more than two fluoride layers in this way, in particular a stack of more than two fluoride layers.

[0037] In a further variation, the method further comprises depositing a metal layer, specifically an aluminum layer, on the substrate before introducing the substrate into the ALD chamber for deposition of the at least one fluoride layer. In this case, the metal or aluminum layer is deposited by an external deposition process outside the ALD chamber that is not atomic layer deposition, for example, by a thermal evaporation process. It is also possible to deposit one or more additional fluoride layers on the metal layer externally, i.e., before the substrate is introduced into the ALD chamber. These fluoride layers are also deposited by a deposition process that is not atomic layer deposition.

[0038] In a further development of this variant, the method includes removing an aluminum oxyhydroxide layer from an aluminum layer deposited on a substrate by atomic layer etching in an ALD chamber. The outer deposition of the aluminum layer is performed by depositing an aluminum oxyhydroxide layer on the surface of the aluminum layer, typically with an overall thickness of about 3 nm. x O y layer, or more generally Al x O y OH z To remove this, an atomic layer etching process can be performed in the ALD chamber before the deposition of at least one fluoride layer by atomic layer deposition. In the atomic layer etching process, similar to atomic layer deposition, individual atomic layers are cyclically removed in two separate self-limiting partial reactions. For this purpose, appropriate reactive gases can be used in the two-part reaction or reaction steps.

[0039] In another development, the method includes converting the aluminum oxyhydroxide layer formed on the aluminum layer into an aluminum fluoride layer by fluorinating the aluminum oxyhydroxide layer in an ALD chamber. For fluorination, typically one of the fluorination active substances described above is used, which is converted into an active fluorine species by photodissociation or by using a plasma, as described above in connection with the ALD process. After conversion to the aluminum fluoride layer, at least one fluoride layer is deposited on the substrate or on the aluminum fluoride layer formed by conversion by atomic layer deposition, as described above.

[0040] In principle, the fluorination described above in connection with the aluminum oxyhydroxide layer on a fluoride layer can also be carried out by atomic layer deposition in an ALD chamber to post-fluorinate or refluorinate the deposited fluoride layer. This may be preferable, for example, when an oxyfluoride / hydroxyfluoride layer is formed on the surface of the fluoride layer. For fluorination, the surface of the fluoride layer is exposed to a fluorination-active substance, which is typically converted by photodissociation using UV / VIS radiation or using a plasma to an active fluorine species that causes refluorination of the fluoride layer.

[0041] The substrate can be heated during the ALD process in the ALD chamber during at least some of the ALD cycles and / or during the refluorination.

[0042] A further aspect of the invention relates to an apparatus for atomic layer deposition of the kind specified in the opening paragraph, further comprising at least one UV / VIS light source for irradiating the fluoride layer with UV / VIS light to anneal at least one potential crystalline defect in the fluoride layer.

[0043] For the advantages provided by this device and its embodiments described below, please refer to the above description of the method and its variants. The UV / VIS light source can be a light source designed to emit UV light (UV light source) or VIS light (VIS light source). It is also possible for the light source to be designed to emit both UV and VIS light.

[0044] At least one UV / VIS light source may be spectrally tunable. Tunable UV / VIS light sources are particularly suitable for the present application, since the spectrum can be easily adapted to different potential crystal defects and different materials. Suitable tunable UV / VIS light sources are, for example, broadband light sources that allow downstream wavelength selection. A suitable example for UV light may be a D2 gas discharge lamp with downstream wavelength selection. Plasma light sources may also be used for this purpose.

[0045] The ALD chamber can be hermetically sealed. The interior of the ALD chamber is stable against fluorinated active substances or reactive fluorine precursors and their conversion products. Conversion products of fluorinated active substances refer to fluorine species and compounds formed therefrom (e.g., HF). Stability should specifically be interpreted as meaning that a passivation layer is formed inside the ALD chamber. Specifically, there should be no formation of volatile fluorine compounds that could precipitate on optical elements or substrates. The ALD chamber, and in particular its interior, can be at least partially manufactured from, for example, metallic materials that typically must be free of Cr and Ti to prevent corrosion. The ALD chamber may be specifically manufactured from Monel steel. The interior of the ALD chamber may also have a fluorine-stable coating to prevent corrosion. Such a coating is preferably applied by a galvanic process. Suitable materials are specifically NiP, Pt, Ni, Cu, or Ru / Rh mixtures. If the apparatus has a plasma source (see below), specifically, metals free of W, Si, and Cr should be used in the ALD chamber.

[0046] In one embodiment, the apparatus includes an activation device for generating a reactive fluorine precursor from a fluorinated active material, the activation device having a plasma source and / or a UV / VIS light source for photodissociation of the fluorinated active material. As described above, in the second reaction step of the ALD cycle, the surface of the growing fluoride layer is exposed to the reactive fluorine precursor generated from the fluorinated active material. For this purpose, the fluorinated active material may be supplied to a plasma source and / or irradiated by a UV / VIS light source that generates UV / VIS light having an energy at least twice as large as the dissociation energy of the fluorinated active material.

[0047] It will be appreciated that the apparatus may also have additional components typical of ALD systems, such as metering devices for metal precursors including valve and mixer assemblies, metering devices for fluorinated active materials including valve and mixer assemblies, metering devices for purge gases or inert gases, vacuum technology for forming a vacuum in the ALD chamber, vacuum locks, etc. In particular, the apparatus may also have stops for plasma shadowing and / or plasma formation. It is also preferred if the apparatus includes devices for optical monitoring of the ALD process, for example, by in situ ellipsometry. When a plasma source is used for the formation of reactive fluorine precursors, the ALD chamber may also include a sensor system for monitoring the plasma in the plasma source.

[0048] A further aspect of the present invention relates to an optical element of the type specified in the introduction, in which a fluoride layer has been deposited by the above-mentioned method and / or using the above-mentioned apparatus. It will be appreciated that the optical element may also have two or more fluoride layers deposited by the above-mentioned ALD process or corresponding apparatus. The optical element may also have one or more fluoride or other layers, such as metal layers, that have not been deposited by atomic layer deposition.

[0049] The optical element may be a transmissive optical element, such as a laser chamber window of an excimer laser, where the exterior of the laser chamber window is entirely coated with a high-density fluoride layer, but the optical element may also be a reflective optical element, such as a mirror that serves to deflect or focus radiation in the VUV wavelength range, or a beam splitter that serves to both transmit and reflect radiation in the VUV wavelength range.

[0050] A further aspect of the invention relates to an optical setup for the VUV wavelength range, in particular a VUV lithography apparatus or a wafer inspection system, comprising at least one optical element as described above. The optical setup may be, for example, a (VUV) lithography system, a wafer or mask inspection system, a laser system, etc.

[0051] Further features and advantages of the invention will become apparent from the following description of an embodiment of the invention, with reference to the figures of the drawing which show the details essential to the invention, and from the claims, in which the individual features can be implemented alone, individually or together in any combination in a variant of the invention.

[0052] Examples are shown in the schematic drawings and explained in the following description. [Brief explanation of the drawings]

[0053] [Figure 1] FIG. 1 is a schematic diagram showing an apparatus for atomic layer deposition of a fluoride layer on a substrate, having two UV light sources for emitting UV light and an excitation device for exciting a fluorinated active material. [Figure 2] 2 is a flow diagram illustrating an ALD process for deposition of a fluoride layer on a substrate in the apparatus of FIG. 1. [Figure 3a] 1 is a flow diagram illustrating two variations of a photo-ALD process for the deposition of a fluoride layer. [Figure 3b] 1 is a flow diagram illustrating two variations of a photo-ALD process for the deposition of a fluoride layer. [Figure 4a]1 is a flow diagram illustrating two variations of a plasma-enhanced ALD process for the deposition of a fluoride layer. [Figure 4b] 1 is a flow diagram illustrating two variations of a plasma-enhanced ALD process for the deposition of a fluoride layer. [Figure 5] 1 is a flow diagram illustrating a process for coating an optical element in which, in addition to the fluoride layer deposited in an ALD process, a further layer is deposited. [Figure 6] 1 is a flow diagram illustrating a coating process in which an oxyhydroxide layer is removed in an ALD chamber prior to deposition of a fluoride layer. [Figure 7] 1 is a flow diagram illustrating an ALD process for deposition of multiple different fluoride layers. [Figure 8] 1 is a schematic diagram showing an optical setup for the VUV wavelength range in the form of a VUV lithography apparatus; [Figure 9] FIG. 1 is a schematic diagram showing an optical setup for the VUV wavelength range in the form of a wafer inspection system. [Figure 10] FIG. 1 is a schematic diagram showing an optical element in the form of a laser chamber window. DETAILED DESCRIPTION OF THE INVENTION

[0054] In the following description of the drawings, the same reference numerals are used for components that are the same or have the same function.

[0055] FIG. 1 shows an apparatus 1 for atomic layer deposition of one or more fluoride layers 2 on a substrate 3. For this purpose, the apparatus 1 comprises an ALD chamber 4 in the form of a vacuum chamber, to which a mount 5 (manipulator) for the substrate 3 in the form of a rotary table is attached. An electric potential (bias) can be applied to the mount 5 in order to accelerate ions from the plasma, for example, towards the substrate 3. The mount 5 can also be heated by means of a heating device (not shown). A vacuum pump 6 serves to create a vacuum inside the ALD chamber 4.

[0056] The apparatus 1 also has a gas supply device 7 designed to supply the gaseous fluorinated active material FW, the gaseous metal precursor MP, and the purge gas or inert gas IG to the ALD chamber 4, and having multiple gas inlets for this purpose. The gas supply device 7 further has a valve or metering mechanism that allows for the controlled delivery of the gaseous fluorinated active material FW, the gaseous metal precursor MP, and the inert gas IG to the interior of the ALD chamber 4. The fluorinated active material FW can also be supplied to an activation device 8, as described in more detail below, and thereby to the interior of the ALD chamber 4.

[0057] The metal precursor MP supplied from the gas reservoir may be, for example, Al(CH3)3, AlCl3, (C2H5)3Al, Mg(tnd)2, Mg(EtCp)2, Ca(thd)2, La(thd)2, or LiHMDS. The fluorinated active material FW is selected depending on the metal component of the fluoride layer 2, which in the illustrated example is a metal fluoride layer. The fluorinated active material FW described herein is capable of depositing a fluoride layer in the form of an AlF3 layer, an MgF2 layer, or an LaF3 layer in an ALD process. In the illustrated example, trimethylaluminum, i.e., Al(CH3)3, is used as the metal precursor MP.

[0058] The inert gas IG may be, for example, a noble gas, such as argon, which may serve purposes including venting the ALD chamber 4 before opening it and establishing pressure inside the ALD chamber 4, and may serve as a purge gas for purging the interior of the ALD chamber 4, specifically between reaction steps A and B of the ALD process. See FIG. 2 .

[0059] The fluorinated active material FW may be, for example, SF6, NF3, HF, HF-pyridine, F2, NHF, CF4, CHF3, TiF4, WF6, MoF5, or TaF5. In the illustrated example, the fluorinated active material used is gaseous SF6. For the implementation of the (partial) reaction step of the ALD process, the use of a fluorinated active material FW is necessary to form a reactive fluorine precursor FP to which the surface of the fluoride layer 2 or substrate 3 is exposed. For this purpose, an activation device 8 is suitable.

[0060] For this purpose, the activation device 8 shown in FIG. 1 includes a (third) light source 9c in the form of a photodissociation light source for photodissociation of the fluorinated active material FW and a plasma source 11. When the fluorinated active material FW is activated by the UV light source 9c, it is introduced directly into the ALD chamber 4 through the gas inlet of the gas supply device 7. In this case, activation is performed by photodissociation of the fluorinated active material FW with light 10c generated by the third light source 9c. The light 10c generated by the third light source 9c has at least one wavelength with a photon energy greater than the dissociation energy of the fluorinated active material FW. Thus, the third light source 9c or the light 10c generated by it is adapted to the fluorinated active material FW used. In the illustrated example, the light 10c from the third light source 9c is radiated onto the fluoride layer 2. The light 10c from the third light source is light 10c in a third spectral region within the useful wavelength range of the optical element formed during the deposition of the fluoride layer 2 on the substrate 3. In the illustrated example, the third spectral region is in the VUV wavelength range.

[0061] When the reactive fluorine precursor FP is generated from the fluorinated active material FW by forming a plasma, the fluorinated active material FW is supplied to the plasma source 11 and activated thereby to form the reactive fluorine precursor FP, which may include, for example, fluorine radicals or fluorine in an excited electronic state. It will be apparent that the activation device 8 does not necessarily have to include both the plasma source 11 and the photodissociation light source 9c. Generally, one of these two sources will be sufficient to generate the reactive fluorine precursor FP.

[0062] The apparatus 1 shown in FIG. 1 also includes first and second UV light sources 9a, 9b, which generate UV light 10a, 10b incident on the surface 2a of the fluoride layer 2. In the example shown in FIG. 1, the first UV light source 9a is designed to emit UV light 10a in a first spectral range, which serves to anneal potential crystalline defects during deposition of the fluoride layer 2 in an atomic layer deposition process. The first spectral range may be at wavelengths greater than 190 nm. The second UV light source 9b is designed to emit UV light 10b in a second spectral range, which serves to mobilize atoms at the surface 2a of the fluoride layer 2. The two spectral ranges are not shown and are selected depending on the deposition material, for example, as described in the aforementioned German Patent Publication No. 102021203505.

[0063] 1, the device 1 may have a single UV light source that emits UV light in both the first and second spectral ranges 10a, 10b. The device may have only a first UV light source 9a that emits UV light in the first spectral range 10a. The device 1 may have more than two UV light sources 9a, 9b.

[0064] In the illustrated example, both the first UV light source 9a and the second UV light source 9b are designed to emit UV light 10a, 10b in fixed first and second spectral ranges, respectively. However, it is also possible for the first and / or second UV light sources 9a, 9b to be adjustable so that the first and / or second spectral ranges can be set or adjusted. In the example shown in Figure 1, the first UV light source 9a is an excimer laser with a wavelength of 193 nm, and the second UV light source 9b is, for example, a D2 lamp emitting light in the wavelength range of 115 nm to 122 nm.

[0065] Alternatively, one or both light sources 9a, 9b may be designed to generate light in the visible wavelength range (VIS light). In this case, the light sources 9a, 9b may be designed to emit VIS light in defined first and second spectral ranges, respectively, or the light sources 9a, 9b may be designed to be adjustable. Also, a single VIS light source may be designed to generate VIS light in both the first and second spectral ranges. It is also possible to provide one or more UV light sources and one or more VIS light sources.

[0066] A method for atomic layer deposition of a fluoride layer, more specifically an AlF layer, in the apparatus 1 of FIG. 1 will now be described with reference to the flow diagram shown in FIG. 2. In this method, in a first step, a substrate 3, e.g., a glass substrate or crystalline form, is fixed on a stage 5, a purge step is performed, and the ALD chamber 4 is evacuated. A first (partial) reaction step A of an ALD cycle Z is then performed, in which the surface of the substrate 3 or an already-deposited portion of the fluoride layer 2 is exposed to a metal precursor MP, and a first surface reaction of the ALD process proceeds on the surface of the fluoride layer 2. After a subsequent purge step, in which residues of the metal precursor MP and volatile reaction products from the first reaction step A are pumped out of the interior of the ALD chamber 4, a second (partial) reaction step B of the ALD cycle Z is performed.

[0067] In the second reaction step B, the surface 2a of the fluoride layer 2 is exposed to a reactive fluorine precursor FP. This occurs by photodissociation or by plasma formation from a fluorinated active material, SF6 in the disclosed example, in the manner described in connection with FIG. 1. The surface reactions that occur in the two reaction steps A and B are described in the paper by MFJ Vos et al. cited above. The two reaction steps A and B, along with their respective subsequent purge steps, form an ALD cycle Z, in which one or more layers of AlF3 are deposited. The ALD cycle Z is repeated n times until the fluoride layer 2 has its desired thickness. Depending on the thickness of the fluoride layer 2, the number of ALD cycles Z, n, may be, for example, about 10 to 500. After growing the fluoride layer 2 to the desired thickness, the substrate 3 is removed from the pedestal and the ALD chamber 4.

[0068] Also seen in FIG. 2, in a second reaction step B, the surface 2a of the substrate 3 or fluoride layer 2 is exposed to UV light 10a from a first UV light source 9a to anneal at least one latent crystalline defect in the fluoride layer 2, as described above in connection with FIG. 1.

[0069] 3a and 3b show two variants of a photo-ALD process for the deposition of a fluoride layer 2. The first variant shown in FIG. 3a corresponds to the variant shown in FIG. 2, in which a fluorinated active substance FW is activated by photodissociation. In the variant shown in FIG. 3b, in addition to the irradiation of the fluoride layer 2 with UV light 10a in the second reaction step B, a bleaching step is performed in a further subsequent process step of the respective ALD cycle Z. In the bleaching step, the surface 2a of the fluoride layer 2 is also irradiated with UV light 10a to anneal potential crystalline defects in the fluoride layer 2. Alternatively, bleaching can be performed independently after the second reaction step B. Also as shown in FIG. 3b, if a layer of, for example, an oxyfluoride / hydroxyfluoride is formed on the surface 2a of the fluoride layer 2 during the bleaching step, a fluorinated active substance FW can be further supplied to the interior of the ALD chamber 4 to cause refluorination of the fluoride layer 2.

[0070] 4a and 4b show two variants of a plasma-enhanced ALD process for the deposition of a fluoride layer 2. The first variant shown in 4a corresponds to the variant shown in 2, in which a fluorinated active material FW is activated by plasma or plasma cracking to form a reactive fluorine precursor FP. In 4b, similar to 3b, the surface 2a of the fluoride layer 2 is irradiated with UV / VIS light 10a in a dedicated bleaching step that occurs after the second reaction step B. Unlike 3b, in the variant shown in 4b, no bleaching occurs in the second reaction step B. However, it should be clear that this is also possible with the plasma-enhanced ALD process described in 4b.

[0071] For the production of optical elements, typically, not only the fluoride layer 2 is deposited on the substrate 3, but generally further layers are also deposited. Figure 5 shows a flow chart of a method in which a first aluminum layer and then a fluoride layer or coating are deposited on the substrate 3 in two preceding steps, before the coated substrate 3 is introduced into an ALD chamber 4 and a fluoride layer 2 is deposited on the coated substrate 3 by atomic layer deposition in the manner described above. The deposition of the aluminum and fluoride layers prior to introduction into the ALD chamber 4 is not performed by atomic layer deposition, but rather by, for example, a thermal evaporation process.

[0072] Figure 6 shows the natural thin film Al on the surface of the aluminum layer after deposition under ambient air. x O y layer or more commonly Al x O y OH z 6 shows a process sequence similar to that of FIG. 5, in which a layer is formed. To remove it, an atomic layer etching process can be performed in the ALD chamber 4 before at least one fluoride layer 2 is deposited by an atomic layer deposition process (variant (a) of FIG. 6). In this case, the apparatus 1 is designed not only for atomic layer deposition but also for atomic layer etching.

[0073] Or Al x O y OH z The aluminum oxide layer is converted into an aluminum fluoride layer by x O y OH z The layer may be removed (variant (b) of FIG. 6). The conversion is carried out using a fluorinated active material FW to which the surface of the aluminum layer is exposed, from which active fluorine species are generated by photodissociation or by plasma, as described above in connection with the ALD process. After conversion to an aluminum fluoride layer in the manner described above, at least one fluoride layer 2 can be deposited by atomic layer deposition on the substrate 3, or more specifically on the aluminum fluoride layer formed by conversion.

[0074] To post-fluorinate or re-fluorinate the deposited fluoride layer 2, it is also possible to carry out the fluorination described above in connection with an aluminum oxyhydroxide layer on a fluoride layer deposited by atomic layer deposition in the ALD chamber 4. This may be preferable, for example, if an oxyfluoride / hydroxyfluoride layer has formed on the surface of the fluoride layer 2. For fluorination, the surface 2a of the fluoride layer 2 is exposed to a fluorinated active substance FW, which is typically converted by photodissociation using UV / VIS light 10c or by using a plasma into active fluorine species that result in re-fluorination of the fluoride layer 2.

[0075] 7 shows a process sequence for the deposition of multiple dielectric functional fluoride layers, which are applied alternately to a substrate 3 to form a functional coating, for example in the form of a reflective or antireflective dielectric coating having n alternating layers of AlF3 and LaF3 in the illustrated example. During the deposition of each fluoride layer 2, the spectral range of the bleaching light, or more specifically the UV light 10a emitted by the first UV light source 9a, is adapted to the metallic material of the fluoride layer 2 to be deposited. More specifically, in the illustrated example, the first spectral range is switched from a wavelength range of approximately 170 nm to 190 nm for the atomic layer deposition of AlF3 to a wavelength of approximately 260 nm for the atomic layer deposition of MgF2.

[0076] Figure 8 shows an optical setup for the VUV wavelength range in the form of a VUV lithography apparatus 21. The VUV lithography apparatus 21 comprises two optical systems: an illumination system 22 and a projection system 23. The VUV lithography apparatus 21 further comprises a radiation source 24, which may for example be an excimer laser.

[0077] Radiation 25 emitted by radiation source 24 is conditioned using illumination system 22 so that mask 26, also called a reticle, is illuminated thereby. In the illustrated example, illumination system 22 has a housing 32 in which both transmissive and reflective optical elements are arranged. The figure exemplarily shows transmissive optical element 27, which focuses radiation 25, and reflective optical element 28, which deflects the radiation.

[0078] The mask 26 has a structure on its surface that is to be transferred onto an optical element 29, e.g., a wafer, that is exposed by means of the projection system 23 in order to manufacture semiconductor components. In the example shown, the mask 26 is designed as a transmissive optical element. In alternative embodiments, the mask 26 can also be designed as a reflective optical element.

[0079] The projection system 23 in the illustrated example comprises at least one transmissive optical element, which typically shows two transmissive optical elements 30, 31 that serve, for example, to reduce the size of structures on the mask 26 to a desired size for exposure of the wafer 29.

[0080] In both illumination system 22 and projection system 23, a variety of transmissive, reflective, or other optical elements can be combined with each other as desired, including in more complex schemes. Optical setups without transmissive optics can also be used for VUV lithography.

[0081] FIG. 9 shows an optical setup for the VUV wavelength range in the form of a wafer inspection system 41, although a mask inspection system may also be included. The wafer inspection system 41 comprises an optical system 42 having a radiation source 54, from which radiation 55 is directed toward a wafer 49 using the optical system 42. For this purpose, a concave mirror 46 reflects the radiation 55 onto the wafer 49. In a mask inspection system, the wafer 49 can be replaced by a mask to be inspected. The radiation reflected, diffracted, and / or refracted by the wafer 49 is directed via a transmissive optical element 47 and by a further concave mirror 48, also associated with the optical system 42, to a detector 50 for further evaluation. The wafer inspection system 41 further comprises a housing 52 in which the two mirrors 46, 48 and the transmissive optical element 47 are arranged. The radiation source 54 may be, for example, exactly one radiation source or a combination of several individual radiation sources to provide a substantially continuous radiation spectrum. In a variant, one or more narrowband radiation sources 54 may also be used.

[0082] At least one of the optical elements 27, 28, 30, 31 of the VUV lithography apparatus 21 shown in Figure 8 and at least one of the optical elements 46, 47, 48 of the wafer inspection system 41 shown in Figure 9 are now designed as described above, and are therefore coated with at least one fluoride layer 2, which has been deposited by the method and / or using the apparatus 1 described above.

[0083] FIG. 10 shows an optical element for transmitting radiation in the VUV wavelength range in the form of a laser chamber window 60 of a laser chamber 61 of an excimer laser 62. The laser beam emitted from the excimer laser 62 passes through the laser chamber window 60 to the exterior. The exterior of the laser chamber window 60 is coated with a fluoride layer 2 deposited by the method and / or using the apparatus described above. During atomic layer deposition, the fluoride layer 2 is irradiated with UV / VIS light 10a to anneal potential crystalline defects, and thus has both a high density and a low absorption coefficient. Sealing with such a layer 2 inhibits degradation of the laser chamber window 60, thus extending its lifetime. [Explanation of symbols]

[0084] 1 device 2. Fluoride layer 2a surface 3. Circuit Board 4. ALD chamber 5 Mounting stand 6. Vacuum pump 7 Gas Supply Device 8 Activation Device 9a First UV / VIS light source 9b Second UV / VIS Light Source 9c Third UV / VIS Light Source 10a UV / VIS light 10b UV / VIS light 10c UV / VIS light 11 Plasma Source 21 VUV lithography equipment 22 Lighting system 23 Projection system 24 Radiation source 25 Radiation 26 Mask 27 Transmitting Optical Elements 28 Reflective Optical Elements 29 Optical elements, wafers 30 Transmitting optical elements 31 Transmitting optical elements 32 Housing 41 Wafer Inspection System 42 Optical system 46 concave mirror 47 Transmitting Optical Elements 48 Concave mirror 49 wafers 50 detectors 52 Housing 54 Radiation source 55 Radiation 60 Laser chamber window 61 Laser Chamber 62 Excimer Laser

Claims

1. A method for depositing at least one fluoride layer (2), comprising the steps of:

1. A method comprising depositing said fluoride layer (2) on a substrate (3) by photo-assisted atomic layer deposition (ALD) in a plurality of ALD cycles (Z), irradiating the fluoride layer (2) with UV / VIS light (10a) at least in some ALD cycles (Z) of the plurality of ALD cycles (Z), in particular in all ALD cycles (Z), to anneal at least one potential crystalline defect in the fluoride layer (2).

2. 2. The method of claim 1, wherein in a first reaction step (A) of each ALD cycle (Z), the fluoride layer (2) is exposed to a metal precursor (MP), and preferably no UV / VIS light (10a) is irradiated onto the fluoride layer (2) in the first reaction step (A) to anneal the at least one latent crystalline defect.

3. The metal precursor (MP) is Al(CH 3 ) 3 , AlCl 3 , (C 2 H 5 ) 3 Al, Mg(thd) 2 , Mg(EtCp) 2 , Ca(thd) 2 , La(thd) 2 and LiHMDS.

4. 4. The method according to claim 1, wherein during and / or after the second reaction step (B) of each ALD cycle (Z) in which the fluoride layer (2) is exposed to a reactive fluorine precursor (FP), the fluoride layer (2) is irradiated with the UV / VIS light (10a) to anneal the at least one latent crystalline defect.

5. 5. The method of claim 4, wherein the reactive fluorine precursor (FP) is generated from a fluorinated active material (FW) by photodissociation.

6. The fluorinated active material (FW) is SF 6 , N.F. 3 , HF, HF-pyridine, F 2 , N.H. 4 F, CF 4 , CHF 3 , TiF 4 , W.F. 6 , MoF 5 , TaF 5 6. The method of claim 4, wherein the compound is selected from the group comprising:

7. 7. The method according to any one of claims 4 to 6, further comprising irradiating the fluoride layer (2) with light (10c) in a third spectral range for photodissociation of the fluorinated active substance (FW), wherein the third spectral range is within a useful wavelength range, in particular a VUV wavelength range, of optical elements (27, 28, 30, 31; 46, 47, 48; 60) formed in the deposition of the at least one fluoride layer (2).

8. 8. The method according to any one of claims 1 to 7, wherein the fluoride layer (2) is irradiated with UV / VIS light (10a) in a first spectral range to anneal the at least one potential crystalline defect, and the fluoride layer (2) is irradiated with light (10b), preferably in a second spectral range, to mobilize atoms on the surface (2a) of the fluoride layer (2).

9. The method of claim 8 , wherein the first spectral region is at wavelengths greater than 190 nm.

10. 10. The method according to claim 8 or 9, wherein at least two fluoride layers (2) having different metal components are deposited on the substrate (3), and the first spectral range upon irradiation of each fluoride layer (2) is adapted to the respective metal component of the fluoride layer (2).

11. 11. The method according to any one of claims 1 to 10, further comprising depositing a metal layer, in particular an aluminum layer, on the substrate (3) before introducing the substrate (3) into an ALD chamber (4) for the deposition of the at least one fluoride layer (2).

12. 12. The method of claim 11, further comprising removing an aluminum oxyhydroxide layer from the aluminum layer by atomic layer etching in the ALD chamber (4).

13. 12. The method of claim 11, further comprising converting the aluminum oxyhydroxide layer formed on the aluminum layer to an aluminum fluoride layer by fluorinating the aluminum oxyhydroxide layer in the ALD chamber (4).

14. An apparatus (1) for atomic layer deposition of at least one fluoride layer (2), comprising: an ALD chamber (4) with a holder (5) for the substrate (3), a gas supply device (7) for supplying a fluorinated active material (FW) to said ALD chamber (4), 1. The apparatus (1), characterized in that the apparatus (1) comprises at least one UV / VIS light source (9a) for irradiating the fluoride layer (2) with UV / VIS light (10a) to anneal at least one potential crystalline defect in the fluoride layer (2).

15. 15. The apparatus according to claim 14, further comprising an activation device (8) for generating reactive fluorine precursors (FP) from said fluorinated active materials (FW), said activation device having a UV / VIS light source (9c) for photodissociation of said fluorinated active materials (FW).

16. An optical element (27, 28, 30, 31; 46, 47, 48; 60) for reflection and / or transmission of radiation (25, 55) in the VUV wavelength range, An optical element (27, 28, 30, 31; 46, 47, 48; 60) comprising a substrate (3) coated with a fluoride layer (2), Optical element (27, 28, 30, 31; 46, 47, 48; 60), characterized in that the fluoride layer (2) has been deposited by a method according to any one of claims 1 to 13 and / or with an apparatus (1) according to any one of claims 14 and 15.

17. 17. An optical setup for the VUV wavelength range, in particular a VUV lithography apparatus (21) or a wafer inspection system (41), comprising at least one optical element (27, 28, 30, 31; 46, 47, 48; 60) according to claim 16.

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