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

Abstract

The invention relates to a method for depositing at least one fluoride layer (2), comprising: depositing the fluoride layer (2) on a substrate (3) by atomic layer deposition, ALD, in a plurality of ALD cycles. The method comprises irradiating the fluoride layer (2) with UV / VIS light (10a) in at least some of the plurality of ALD cycles, in particular in all ALD cycles, in order to anneal at least one potential crystal defect in the fluoride layer (2). The invention also relates to a device (1) for atomic layer deposition of at least one fluoride layer (2), an optical element having a substrate (3) coated with such a fluoride layer (2), and an optical arrangement having at least one such optical element.

Description

Background of the invention

[0001] The invention relates to a method for depositing a fluoride layer, comprising: depositing the fluoride layer on a substrate by atomic layer deposition (ALD) in a plurality of ALD cycles. The invention also relates to an apparatus for atomic layer deposition of at least one fluoride layer, comprising: an ALD chamber with a holder for a substrate, and a gas supply device for supplying a fluorination agent into the ALD chamber. The invention further relates to an optical element for reflecting and / or transmitting radiation in the VUV wavelength range, which has a substrate coated with a fluoride layer, and to an optical arrangement for the VUV wavelength range, which has at least one such optical element.

[0002] In this application, the VUV wavelength range refers to the wavelength range of electromagnetic radiation between 115 nm and 190 nm. The VUV wavelength range is particularly important for microlithography. Radiation in the VUV wavelength range is used, for example, in projection exposure systems and wafer or mask inspection systems.

[0003] Such systems often employ optical elements that have at least one fluoride layer. Highly reflective optical elements for the VUV wavelength range, for example, typically have a fluoride layer to protect an underlying metal layer, which reflects the radiation, from oxidation. Layer stacks of different fluorides, or fluorides and possibly oxides, can also be used to add a mirror or anti-reflective coating to optical elements. However, high radiation intensities, such as those required in wafer or mask inspection systems and projection exposure systems, lead to degradation of the fluorides and the optical elements in general, which shortens their service life.

[0004] DE 10 2021 201 477 A1 describes a method for operating an optical arrangement comprising at least one optical element containing a fluoride. The optical arrangement comprises a regeneration radiation arrangement that provides electromagnetic regeneration radiation at UV wavelengths to irradiate the optical element and cause defects in the fluoride to heal.

[0005] Degradation can also be counteracted by high-density fluoride layers. High-density fluoride layers can generally be deposited using physical vapor deposition (PVD), e.g., sputter deposition. Chemical vapor deposition (CVD), particularly atomic layer deposition (ALD), is a particularly promising technology for the deposition of fluoride layers or, in general, layers for optical elements.

[0006] In atomic layer deposition, several ALD cycles are run sequentially, with one or more layers of a film being deposited in each ALD cycle. An ALD cycle comprises two or more reaction steps, each of which involves 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 referred to as a co-reactant, in a second reaction step to reactivate the surface for the first reaction step. A rinsing step usually takes place between each two reaction steps.

[0007] Atomic layer deposition for depositing layers on optical elements is described in the literature, including the following documents: US 2023 / 0123796 A1 describes an optical component made of crystalline calcium fluoride with a conformal coating deposited by atomic layer deposition. DE 10 2018 211 499 A1 describes a method for producing an optical element for the VUV wavelength range, in which at least two layers are applied to a substrate by atomic layer deposition.

[0008] WO 2021 / 021436 A1 describes an atomic layer deposition process for coating an optical lens with a magnesium fluoride layer, in which a magnesium oxide layer is first formed, which is subsequently converted into the magnesium fluoride layer.

[0009] WO 2023 / 101862 A1 describes protective coatings for aluminum mirrors. To produce these coatings, an aluminum layer is deposited onto a glass substrate using a physical deposition process. A first and second fluorine-containing layer, e.g., made of MgF2 or AlF3, are deposited onto the aluminum layer using a physical deposition process. A third fluorine-containing layer is deposited onto the second fluorine-containing layer using an atomic layer deposition process. Before the first fluorine-containing layer is deposited, a native aluminum oxide layer can be removed from the surface of the aluminum layer using an atomic layer etching process.

[0010] While thermal ALD processes are generally unattractive due to the elevated temperature involved in coating optical components, photo-assisted ALD processes or those based on the use of plasma are particularly promising: US Pat. No. 7,798,096 B2 describes the use of UV light to assist the deposition of high-k dielectrics using chemical vapor deposition or atomic layer deposition. The UV light is used to excite or ionize the process gas and thereby initiate or enhance surface reactions during deposition.

[0011] US 2005 / 0148206 A1 describes an ALD process in which electromagnetic radiation is applied to a layer during or after it is exposed to a second reactant in order to destabilise unwanted bonds, in particular metal-metal bonds, by excitation and to convert them into the desired bond form.

[0012] US 2017 / 0058401 A1 describes a photo-assisted ALD process for metals in which light is used to dissociate a precursor. To dissociate the precursor as efficiently as possible, different wavelengths can be offered.

[0013] In the article “Photo-Assisted ALD: Process Development and Application Perspectives”, V. Miikkulainen, 2017 ECS Trans. 80 49, it is described that photo-assisted ALD can simplify the so-called selective-area ALD and photo-assisted ALD processes for metal oxides and metals are described, using, among other things, D2 lamps.

[0014] The article "Atomic layer deposition of aluminum fluoride using Al(CH3)3 and SF6 plasma," by MFJ Vos et al., Applied Physics Letters 111, 113105 (2017), describes the deposition of a dense layer of AlF3 using trimethylaluminum (Al(CH3)3) as a precursor and an SF6 plasma as a co-reactant at temperatures between 50°C and 300°C. The article and the Supplementary Material to this article provide extinction coefficients of the deposited AlF3 layer. The extinction coefficients reported there for the VUV wavelength range are comparatively large and increase with decreasing deposition temperature, resulting in low optical performance of the deposited AlF3 layers. The article suggests that the larger extinction coefficient at a deposition temperature of 50°C is due to a higher proportion of sulfur in the environment. Object of the invention

[0015] The object of the invention is to provide a method and a device for the atomic layer deposition of fluoride layers which have a high optical performance, as well as to provide an optical element and an optical arrangement comprising such an optical element. Subject of the invention

[0016] According to a first aspect, this object is achieved by a method of the type mentioned above, which comprises the following additional step: irradiating the fluoride layer with UV / VIS light at least in a portion of the plurality of ALD cycles, in particular in all ALD cycles, in order to heal at least one potential crystal defect in the fluoride layer. The fluoride layer is typically a metal fluoride layer.

[0017] The inventors have recognized that a disadvantage of photo-assisted ALD processes and plasma 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 leads to the formation of defects (e.g., color centers) in the fluoride layer. These defects can arise, in particular, in the volume of the growing layer and have a negative impact on both the optical performance, i.e., on the absorption in the desired wavelength range, in this case the VUV wavelength range, and on the lifetime of the optical components. These defects occur particularly at a comparatively low deposition temperature and are the actual cause of the larger extinction coefficients described in the above-cited article by MFJ Vos.

[0018] To resolve the technical contradiction between a desirably low deposition temperature in the ALD process on the one hand and a defect-free growing solid on the other, the inventors propose that additional light be provided during the ALD process, particularly during a photo-assisted ALD process or a plasma ALD process, to heal the crystal defects that typically or potentially arise. Irradiation with UV / VIS radiation to heal crystal defects that typically or potentially arise during the deposition of the fluoride layer can occur in each of the ALD cycles; however, it is also possible for the irradiation to be performed only in some of the ALD cycles, e.g., every second, third, fourth, etc. ALD cycle, provided this is sufficient to heal the potential crystal defects in the bulk of the fluoride layer.

[0019] For the purposes of this application, UV light is understood to mean electromagnetic radiation in a wavelength range between 100 nm and 380 nm. For the purposes of this application, VIS light is understood to mean radiation in a wavelength range between 380 nm and 830 nm. For the purposes of this application, UV / VIS light is understood to mean radiation in a wavelength range between 100 nm and 380 nm (UV light) and / or between 380 nm and 830 nm (VIS light). The UV / VIS wavelength range can be further restricted and, for example, lie between 170 nm and 730 nm. Irradiation with UV / VIS light does not generally take place in the entire UV / VIS wavelength range, but in one or more selected spectral ranges that are adapted to the respective crystal defect to be healed, in particular in the form of a color center, for example an F center. A respective spectral range can, if necessary,only comprise a single wavelength, for example when the UV / VIS light is generated by a laser source, e.g. an excimer laser.

[0020] The selection of suitable wavelengths can be carried out, for example, in the manner described in DE 10 2021 203 505 A1, which is incorporated by reference in its entirety into this application. There, it is described that a layer of an ionically bonded solid is deposited on a substrate by transferring a coating material into the gas phase and depositing the gas-phased coating material onto the substrate. During deposition, the layer is irradiated with UV / VIS light in a first spectral range that at least partially overlaps with an absorption range of at least one (potential) crystal defect in order to instantly heal the (potential) crystal defect arising during deposition of the coating material.

[0021] In one variant of the method according to the invention, the fluoride layer is exposed to a metallic precursor in a first reaction step of a respective ALD cycle, wherein the fluoride layer is preferably not irradiated with UV / VIS light in the first reaction step in order to heal the at least one potential crystal defect. The deposited fluoride layer is typically a metal fluoride layer deposited with the aid of a metallic precursor. Irradiation with UV / VIS light to heal potential crystal defects during the first reaction step is generally not advantageous, among other things because the metallic precursor can be undesirably excited or dissociated by the UV / VIS light, which has a detrimental effect on layer formation.

[0022] In a further development of this variant, the metallic precursor is selected from the group comprising: Al(CH3)3, AlCl3, (C2H5)3Al, Mg(thd)2, Mg(EtCp)2, Ca(thd)2, La(thd)2, and LiHMDS. The metallic precursor is chosen depending on the type of fluoride layer to be deposited during the ALD process. For example, if the layer is an AlF3 layer, Al(CH3)3, i.e., trimethylaluminum (TMA), AlCl3, i.e., trichloroaluminum, or (C2H5)3Al, i.e., triethylaluminum, can be used. For a MgF2 layer, for example, Mg(thd)2 or Mg(EtCp)2 can be used, where "thd" stands for 2,2,6,6-tetramethyl-3,5-heptanedionato and "EtCp" for ethylcyclopentadienyl. For a CaF2 layer, for example, Ca(thd)2 can be used, for an LaF3 layer, for example, La(thd)2, and for a LiF layer, for example, LiHMDS, i.e., lithium hexamethyldisilazide, can be used as the metallic precursor.

[0023] In a further variant, the fluoride layer is irradiated with UV / VIS light in order to heal the at least one potential crystal defect during and / or after a second reaction step of a respective ALD cycle, in which the fluoride layer is exposed to a reactive fluorine precursor. In this variant, the reactive fluorine precursor is typically generated by exciting a fluorination agent, wherein the excitation can be achieved by a plasma or by electromagnetic radiation, i.e. by light. The inventors have recognized that it is advantageous to carry out the irradiation with UV / VIS light to heal the at least one potential crystal defect, also called "bleaching", during the second reaction step or in a separate bleaching step after the second reaction step.In the event that bleaching is carried out in a separate bleaching step, it may be beneficial if the fluoride layer is also exposed to a fluorination agent during the additional bleaching step.

[0024] In a further development of this variant, the reactive fluorine precursor is generated from a fluorination agent by plasma generation. The atomic layer deposition process can, for example, be carried out as in the article by MFJ Vos et al. cited at the beginning, which is incorporated into this application in its entirety by reference. In the ALD process described therein, SF6 gas is used as the fluorination agent, from which an inductively coupled plasma is generated in a plasma source. This plasma can be used as a reactive fluorine precursor or as reactive fluorine species, e.g., F, F2, SF4, and SF 5+ -ions and F -ions. It also describes that other fluorination agents, such as HF or HF-pyridine, can be used in a plasma ALD process.

[0025] In another variant, the reactive fluorine precursor is generated by photodissociation from a fluorination agent. In this variant, the fluorination agent is irradiated with light, typically UV / VUV light, that has at least one wavelength whose energy is at least as great as the dissociation energy of the fluorination agent. A deuterium lamp, for example, can serve as the light source for the photodissociation, emitting light almost continuously in a wavelength range between approximately 180 nm and approximately 800 nm.

[0026] In a further development, the fluorination agent is selected from the group comprising: SF6, NF3, HF, HF-pyridine, F2, NH4F, CF4, CHF3, TiF4, WF6, MoF5, TaF5. As described above, the fluorination agent, which is typically present in the gas phase, can be activated by photodissociation or plasma formation, i.e., converted into a reactive fluorine precursor, so that the second (partial) reaction step of a respective ALD cycle can take place on the surface of the fluoride layer. As described above, it can be advantageous if the irradiation with UV / VIS light takes place, alternatively or in addition to the irradiation in the second reaction step, in a separate bleaching step in which the fluoride layer is exposed to a fluorination agent without this being activated.

[0027] In a further variant, the fluoride layer is irradiated with UV / VIS light in a first spectral range to heal the at least one potential crystal defect, wherein the fluoride layer is preferably irradiated with UV / VIS light in a second spectral range to mobilize atoms on its surface. As described above and in DE 10 2021 203 505 A1, the first spectral range or a suitable wavelength for healing the potential crystal defect depends on the absorption energy of the crystal defect or the anion-cation distance in the fluoride layer. For example, for an AlF3 layer, the first spectral range can be between approximately 170 nm and 190 nm, and for an MgF2 layer or an LaF3 layer, it can be in or near a central wavelength of 260 nm.The fluoride layer can also be irradiated with UV / VIS light in a second spectral range to mobilize atoms on its surface, as also described in DE 10 2021 203 505 A1. The second spectral range can, for example, be in an energy range between 75% and 100%, preferably between 80% and 95%, of the band gap energy of the fluoride layer.

[0028] In a further development of this variant, at least two fluoride layers with different metallic components are deposited on the substrate, wherein the first spectral range is adapted to the respective metallic component during irradiation of the fluoride layer. As described above, the first spectral range for healing the at least one potential crystal defect can be selected or adapted depending on the metallic component of the fluoride layer, which in this case is a metal fluoride layer. It is understood that more than two fluoride layers can also be deposited in this way, in particular layer stacks consisting of more than two fluoride layers.

[0029] In a further variant, the method additionally comprises: depositing a metal layer, in particular an aluminum layer, on the substrate before introducing the substrate into an ALD chamber for depositing the at least one fluoride layer. In this case, the deposition of the metal layer or the aluminum layer takes place using an external deposition process outside the ALD chamber which is not atomic layer deposition, for example using a thermal evaporation process. It is also possible to deposit one or more further fluoride layers externally on the metal layer, i.e. before the substrate is introduced into the ALD chamber. These fluoride layers are also deposited using a deposition process which is not atomic layer deposition.

[0030] In a further development of this variant, the process comprises: removing an aluminum oxyhydroxide layer from the aluminum layer deposited on the substrate by atomic layer etching in the ALD chamber. During external deposition of the aluminum layer, an Al layer with a thickness of approximately 3 nm is typically formed. x O y -layer or more generally an Al x O y OH z -layer on the surface of the aluminum layer. To remove these, an atomic layer etching process can be performed in the ALD chamber before the at least one fluoride layer is deposited by the atomic layer deposition process. In an atomic layer etching process, similar to an atomic layer deposition process, individual atomic layers are cyclically removed in two separate, self-limiting partial reactions. For this purpose, suitable reactive gases can be used in both partial reactions or reaction steps.

[0031] In an alternative development, the method comprises converting an aluminum oxyhydroxide layer formed on the aluminum layer into an aluminum fluoride layer by fluorinating the aluminum oxyhydroxide layer in the ALD chamber. Typically, one of the fluorination agents described above is used for the fluorination, which is converted into active fluorine species by photodissociation or by a plasma, as described above in connection with the ALD process. After conversion into the aluminum fluoride layer, at least one fluoride layer is deposited by atomic layer deposition on the substrate or on the aluminum fluoride layer formed by the conversion in the manner described above.

[0032] In principle, it is possible to perform the fluorination described above in connection with the aluminum oxyhydroxide layer on the fluoride layer deposited by atomic layer deposition in the ALD chamber in order to perform post-fluorination or refluorination of the deposited fluoride layer. This can be advantageous, for example, if a layer of oxyfluoride / hydroxyfluoride has formed on the surface of the fluoride layer. For fluorination, the surface of the fluoride layer is exposed to a fluorination agent. This agent is typically converted into active fluorine species by photodissociation using UV / VIS radiation or by means of a plasma, which cause the refluorination of the fluoride layer.

[0033] It is possible to heat the substrate during the ALD process in the ALD chamber at least in a part of the majority of ALD cycles and / or during refluorination.

[0034] A further aspect of the invention relates to an apparatus for atomic layer deposition of the type mentioned above, further comprising: at least one UV / VIS light source for irradiating the fluoride layer with UV / VIS light in order to heal at least one potential crystal defect of the fluoride layer.

[0035] Regarding the advantages achieved with the device and its embodiments described below, reference is made to the above statements regarding the method and its variants. The UV / VIS light source can be a light source designed to emit UV light (UV light source) or to emit VIS light (VIS light source). It is also possible for the light source to be designed to emit both UV light and VIS light.

[0036] It is possible that at least one UV / VIS light source is spectrally tunable. Tunable UV / VIS light sources are particularly well suited for this application because their spectrum can be easily adapted to various potential crystal defects and different materials. Suitable tunable UV / VIS light sources include broadband light sources that allow for downstream wavelength selection. For UV light, this could be, for example, a D2 gas discharge lamp with downstream wavelength selection. A plasma light source can also be used for this purpose.

[0037] The ALD chamber can be sealed gas-tight. The interior of the ALD chamber is resistant to the fluorination agent or the reactive fluorine precursor and its derivatives. The derivatives of the fluorination agent are understood to be the fluorine species and the chemical compounds formed from them (e.g., HF). This resistance is understood in particular in the sense that a passivating layer forms on the interior of the ALD chamber. In particular, no volatile fluorine compounds must form that could precipitate on the optical element or the substrate. The ALD chamber, in particular its interior, can, for example, be made at least partially of a metallic material that should typically be free of Cr and Ti to prevent corrosion. The ALD chamber can, in particular, be made of Monel steel.The interior of the ALD chamber can also be coated with a fluorine-resistant coating to prevent corrosion. Such a coating is preferably applied using an electroplating process. Suitable materials include NiP, Pt, Ni, Cu, or Ru / Rh mixtures. If the device includes a plasma source (see below), W, Si, and Cr-containing metals should be avoided in the ALD chamber.

[0038] In one embodiment, the device comprises an activation device for generating a reactive fluorine precursor from the fluorination agent, which has a plasma source and / or a UV / VIS light source for photodissociating the fluorination agent. As described above, in the second reaction step of the ALD cycle, the surface of the growing fluoride layer is exposed to a reactive fluorine precursor generated from the fluorination agent. For this purpose, the fluorination agent can be supplied to a plasma source and / or irradiated by a UV / VIS light source that generates UV / VIS light with an energy at least as great as the dissociation energy of the fluorination agent.

[0039] It is understood that the device may also comprise other components typical for ALD systems, for example, dosing devices for the metallic precursor including valves and mixer taps, dosing devices for the fluorination agent including valves and mixer taps, dosing devices for purge gas or an inert gas, vacuum technology for generating a vacuum in the ALD chamber, vacuum locks, etc. In particular, the device may also comprise apertures for plasma shading and / or plasma shaping. It is also advantageous if the device comprises a device for optical monitoring of the ALD process, for example, by in-situ ellipsometry. If a plasma source is used to generate the reactive fluorine precursor, the ALD chamber may also comprise sensors for monitoring the plasma of the plasma source.

[0040] A further aspect of the invention relates to an optical element of the type mentioned above, in which the fluoride layer was deposited by the method described above and / or by means of the device described above. It is understood that the optical element may also comprise two or more fluoride layers deposited by means of the ALD process described above or the corresponding device. The optical element may additionally comprise one or more fluoride layers or other layers that were not deposited by atomic layer deposition, e.g., metallic layers.

[0041] The optical element can be a transmissive optical element, such as the laser chamber window of an excimer laser. In this case, the outer surface of the laser chamber window is typically coated with a high-density fluoride layer. However, the optical element can also be a reflective optical element, such as a mirror used to deflect or focus radiation in the VUV wavelength range, or a beam splitter used to both transmit and reflect radiation in the VUV wavelength range.

[0042] A further aspect of the invention relates to an optical arrangement for the VUV wavelength range, in particular a VUV lithography system or a wafer inspection system, comprising at least one optical element as described above. The optical arrangement can be, for example, a (VUV) lithography system, a wafer or mask inspection system, a laser system, etc.

[0043] 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

[0044] Examples of embodiments are shown in the schematic drawing and are explained in the following description. Fig. 1 is a schematic representation of an apparatus for the atomic layer deposition of fluoride layers on a substrate, comprising two UV light sources for emitting UV light and an excitation device for exciting a fluorination agent, Fig. 2 a flow diagram of an ALD process for depositing a fluoride layer on the substrate in the device of Fig. 1, Fig. 3a,b Flow diagrams of two variants of a photo-ALD process for depositing the fluoride layer, Fig. 4a,b Flow diagrams of two variants of a plasma ALD process for depositing the fluoride layer, Fig. 5 is a flow diagram of a coating process of an optical element in which further layers are deposited in addition to the fluoride layer deposited in the ALD process, Fig. 6 a flow diagram of a coating process in which an oxyhydroxide layer is removed in an ALD chamber before the fluoride layer is deposited, Fig. 7 a flow diagram of an ALD process for depositing several different fluoride layers, Fig. 8 a schematic representation of an optical arrangement for the VUV wavelength range in the form of a VUV lithography system, Fig. 9 a schematic representation of an optical arrangement for the VUV wavelength range in the form of a wafer inspection system, and Fig. 10 a schematic representation of an optical element in the form of a laser chamber window.

[0045] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0046] Fig. 1 shows a device 1 for the atomic layer deposition of one or more fluoride layers 2 on a substrate 3. For this purpose, the device 1 comprises an ALD chamber 4 in the form of a vacuum chamber, in which a holder 5 (manipulator) for the substrate 3 is mounted in the manner of a turntable. An electrical potential (bias) can be applied to the holder 5, for example, to accelerate ions from a plasma toward the substrate 3. The holder 5 can also be heated using a heating device (not shown). A vacuum pump 6 serves to generate a vacuum in an interior of the ALD chamber 4.

[0047] The device 1 also comprises a gas supply device 7, which is designed to supply a gaseous fluorination agent FW, a gaseous metallic precursor MP, and a purge or inert gas IG into the ALD chamber 4 and which has several gas inlets for this purpose. The gas supply device 7 also comprises a valve or metering arrangement that enables a controlled supply of the gaseous fluorination agent FW, the gaseous metallic precursor MP, and the inert gas IG into the interior of the ALD chamber 4. The fluorination agent FW can also be supplied to an activation device 8, via which it enters the interior of the ALD chamber 4, as described in more detail below.

[0048] The metallic precursor MP supplied from a gas reservoir can be, for example, Al(CH3)3, AlCl3, (C2H5)3Al, Mg(thd)2, Mg(EtCp)2, Ca(thd)2, La(thd)2, or LiHMDS. The fluorination agent FW is selected depending on the metallic component of the fluoride layer 2, which in the example shown is a metal fluoride layer. The fluorination agents FW described here are suitable for depositing a fluoride layer 2 in the form of an AlF3 layer, an MgF2 layer, or an LaF3 layer in an ALD process. In the example shown, trimethylaluminum, i.e., Al(CH3)3, is used as the metallic precursor MP.

[0049] The inert gas IG can be, for example, a noble gas, e.g. argon, which can be used, among other things, to ventilate the ALD chamber 4 before opening, to adjust a pressure in the interior of the ALD chamber 4 and in particular as a purge gas for purging the interior of the ALD chamber 4 between reaction steps A, B of the ALD process, cf. Fig. 2.

[0050] The fluorination agent FW can be, for example, SF6, NF3, HF, HF-pyridine, F2, NH4F, CF4, CHF3, TiF4, WF6, MoF5, or TaF5. In the example shown, gaseous SF6 is used as the fluorination agent. To carry out a (partial) reaction step of the ALD process, it is necessary to generate a reactive fluorine precursor FP from the fluorination agent FW, to which the surface of the fluoride layer 2 or the substrate 3 is exposed. The activation device 8 serves this purpose.

[0051] The Fig. For this purpose, the activation device 8 shown in Figure 1 comprises a (third) UV light source 9c in the form of a photodissociation light source for photodissociating the fluorination agent FW, as well as a plasma source 11. If the fluorination agent FW is activated by the UV light source 9c, it is introduced directly into the interior of the ALD chamber 4 via a gas inlet of the gas supply device 7. In this case, activation occurs through photodissociation of the fluorination agent FW by UV light 10c generated by the UV light source 9c. The UV light 10c generated by the UV light source 9c has at least one wavelength whose photon energy is greater than the dissociation energy of the fluorination agent FW. The UV light source 9c or the UV light 10c generated by it is thus adapted to the fluorination agent FW used.

[0052] In the event that the reactive fluorine precursor FP is generated from the fluorination agent FW by forming a plasma, the fluorination agent FW is fed to the plasma source 11, which activates it and forms the reactive fluorine precursor FP, which may, for example, comprise fluorine radicals or fluorine in an excited electronic state. It is understood that the activation device 8 does not necessarily have to comprise both the plasma source 11 and the photodissociation light source 9c: Typically, one of these two sources is sufficient to generate the reactive fluorine precursor FP.

[0053] The Fig. The device 1 shown in Figure 1 also has a first and a second UV light source 9a, 9b, which serve to generate UV light 10a, 10b, which is irradiated onto the surface 2a of the fluoride layer 2. In the Fig. In the example shown in Figure 1, the first UV light source 9a is configured to emit UV light 10a in a first spectral range, which serves to heal potential crystal defects during the deposition of the fluoride layer 2 in the atomic layer deposition process. The second UV light source 9b is configured 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 illustrated and are selected depending on the deposited material. The selection can be carried out, for example, in the manner described in DE 10 2021 203 505 A1 cited above.

[0054] Deviating from the representation of Fig. 1, the device 1 can have a single UV light source that emits UV light 10a, 10b in both the first spectral range and the second spectral range. The device can also have only the first UV light source 9a, which emits UV light 10a in the first spectral range. The device 1 can also have more than two UV light sources 9a, 9b.

[0055] In the example shown, both the first UV light source 9a and the second UV light source 9b are configured to emit UV light 10a, 10b in a fixed, predetermined first and second spectral range, respectively. However, it is also possible for the first and / or second UV light source 9a, 9b to be tunable in order to adjust or tune the first and / or second spectral range. Fig. 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 a D2 lamp.

[0056] Alternatively, one or both light sources 9a, 9b can be configured to generate light in the visible wavelength range (VIS light). In this case, the light sources 9a, 9b can be configured to emit VIS light in a predetermined first or second spectral range, respectively, or the light sources 9a, 9b can be configured to be tunable. A single VIS light source can also be configured to generate VIS light in both the first spectral range and the second spectral range. One or more UV light sources and one or more VIS light sources can also be provided.

[0057] The following describes the atomic layer deposition process of a fluoride layer, more precisely an AlF3 layer, in the device 1 of Fig. 1 based on the Fig. 2. In the method, in a first step, the substrate 3, e.g. in the form of a glass substrate or a crystal, is attached to the holder 5, a rinsing step is carried out and the ALD chamber 4 is evacuated. Subsequently, a first (partial) reaction step A of an ALD cycle Z is carried out, in which the substrate 3 or the surface of the already deposited part of the fluoride layer 2 is exposed to the metallic precursor MP and a first surface reaction of the ALD process takes place on the surface of the fluoride layer 2. After a subsequent rinsing step, in which residues of the metallic precursor MP and volatile reaction products of 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 carried out.

[0058] In the second reaction step B, the surface 2a of the fluoride layer 2 is exposed to the reactive fluorine precursor FP. This is applied to the Fig. 1, either by photodissociation or by the formation of a plasma from the fluorination agent FW, which in the example shown is SF6. The surface reactions taking place in the two reaction steps A and B are described in the article by MFJ Vos et al. cited at the beginning. The two reaction steps A and B as well as the subsequent rinsing 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 predetermined thickness. The number n of ALD cycles Z can, depending on the thickness of the fluoride layer 2, be between approximately 10 and 500, for example. After the fluoride layer 2 has grown to the desired thickness, the substrate 3 is disassembled and removed from the ALD chamber 4.

[0059] As in Fig. 2, in the second reaction step B, the substrate 3 or the surface 2a of the fluoride layer 2 is exposed to the UV light 10a of the first UV light source 9a in order to heal at least one potential crystal defect of the fluoride layer 2, as described above in connection with Fig. 1 was described.

[0060] Fig. 3a,b show two variants of a photo-ALD process for depositing the fluoride layer 2, of which the Fig. 3a shows the first variant of the Fig. 2, in which the activation of the fluorination agent FW occurs by photodissociation. In the case of the Fig. In the variant shown in Figure 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 carried out in a further, subsequent process step of a respective ALD cycle Z, in which the surface 2a of the fluoride layer 2 is also irradiated with the UV light 10a in order to heal potential crystal defects of the fluoride layer 2. Alternatively, the bleaching can be carried out only after the second reaction step B. As in Fig. 3b is also shown, in the bleaching step in the interior of the ALD chamber 4, a fluorination agent FW can additionally be offered in order to effect a refluorination of the fluoride layer 2, for example if a layer of an oxyfluoride / hydroxyfluoride has formed on the surface 2a of the fluoride layer 2.

[0061] Fig. 4a,b show two variants of a plasma ALD process for depositing the fluoride layer 2, of which the Fig. 4a shows the first variant of the Fig. 2, in which the activation of the fluorination agent FW to form the reactive fluorine precursor FP is carried out by a plasma or by plasma cracking. In Fig. 4b is analogous to Fig. 3b, after the second reaction step B, a separate bleaching step is carried out in which the surface 2a of the fluoride layer 2 is irradiated with UV / VIS light 10a. Unlike in Fig. 3b is used in the Fig. 4b, no bleaching is carried out during the second reaction step B. However, it is understood that this also applies to the variant shown in Fig. 4b described plasma ALD process is possible.

[0062] To produce an optical element, typically not only the fluoride layer 2 is deposited on the substrate 3, but usually additional layers. Fig. Figure 5 shows a flow diagram of a process in which, in two preceding steps, an aluminum layer and subsequently a fluoride layer or a fluoride coating are first deposited on the substrate 3. Before the coated substrate 3 is introduced into the ALD chamber 4, 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 layer and the fluoride layer before introduction into the ALD chamber 4 is not carried out by atomic layer deposition, but rather, for example, by a thermal evaporation process.

[0063] Fig. 6 shows a process flow analogous to Fig. 5, in which, after deposition of the aluminum layer in ambient air, a native, thin Al x O y -layer or more generally an Al x O y OH z-layer has formed on the surface of the aluminum layer. To remove this, an atomic layer etching process can be carried out in the ALD chamber 4 before the at least one fluoride layer 2 is deposited by the atomic layer deposition process (variant (a) in Fig. 6). In this case, the device 1 is designed not only for atomic layer deposition, but also for atomic layer etching.

[0064] Alternatively, the Al x O y OH z -layer can be removed from the surface of the aluminum oxide layer by converting it into an aluminum fluoride layer (variant (b) in Fig. 6). For the conversion, a fluorination agent (FW) is used, to which the surface of the aluminum layer is exposed, and from which active fluorine species are generated by photodissociation or by a plasma, as described above in connection with the ALD process. After conversion into the aluminum fluoride layer, at least one fluoride layer 2 can be deposited by atomic layer deposition on the substrate 3, more precisely on the aluminum fluoride layer created by the conversion, in the manner described above.

[0065] It is also possible to perform the fluorination described above in connection with the aluminum oxyhydroxide layer on the fluoride layer deposited by atomic layer deposition in the ALD chamber 4 in order to perform post-fluorination or refluorination of the deposited fluoride layer 2. This can be advantageous, for example, if a layer of an oxyfluoride / hydroxyfluoride has formed on the surface of the fluoride layer 2. For fluorination, the surface 2a of the fluoride layer 2 is exposed to a fluorination agent FW. This is typically converted into active fluorine species by photodissociation using UV / VIS light 10c or by means of a plasma, which cause the refluorination of the fluoride layer 2.

[0066] Fig. Figure 7 shows a process sequence for depositing multiple dielectric functional fluoride layers, which are alternately applied to the substrate 3 to create a functional coating, for example in the form of a reflective or anti-reflective dielectric coating, which in the example shown has a number n of alternating layers of AlF3 and LaF3. During the deposition of each fluoride layer 2, the bleaching light, more precisely the spectral range of 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 precisely, in the example shown, the first spectral range is switched from a wavelength range between approximately 170 nm and 190 nm for the atomic layer deposition of AlF3 to a wavelength of approximately 260 nm for the atomic layer deposition of MgF2.

[0067] Fig. 8 shows an optical arrangement for the VUV wavelength range in the form of a VUV lithography system 21. The VUV lithography system 21 comprises two optical systems, namely an illumination system 22 and a projection system 23. The VUV lithography system 21 also has a radiation source 24, which can be, for example, an excimer laser.

[0068] The radiation 25 emitted by the radiation source 24 is processed by the illumination system 22 to illuminate a mask 26, also called a reticle. In the example shown, the illumination system 22 has a housing 32 in which both transmitting and reflecting optical elements are arranged. Representative elements are a transmitting optical element 27, which focuses the radiation 25, and a reflecting optical element 28, which deflects the radiation.

[0069] The mask 26 has a structure on its surface that is transferred to an optical element 29 to be exposed, for example, a wafer for the production of semiconductor components, using the projection system 23. 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.

[0070] In the example shown, the projection system 23 has at least one transmitting optical element. Two transmitting optical elements 30, 31 are shown as representative elements, which serve, for example, to reduce the structures on the mask 26 to the desired size for exposing the wafer 29.

[0071] In both the illumination system 22 and the projection system 23, a wide variety of transmitting, reflecting, or other optical elements can be combined in any desired, even more complex, way. Optical arrangements without transmissive optical elements can also be used for VUV lithography.

[0072] Fig. 9 shows an optical arrangement for the VUV wavelength range in the form of a wafer inspection system 41, but it can also be a mask inspection system. The wafer inspection system 41 has an optical system 42 with a radiation source 54, the radiation 55 of which is directed onto a wafer 49 by means of the optical system 42. For this purpose, the radiation 55 is reflected onto the wafer 49 by a concave mirror 46. In a mask inspection system, a mask to be examined could be arranged instead of the wafer 49. The radiation reflected, diffracted, and / or refracted by the wafer 49 is guided by a further concave mirror 48, also belonging to the optical system 42, via a transmitting optical element 47 to a detector 50 for further analysis. The wafer inspection system 41 also has a housing 52 in which the two mirrors 46, 48 and the transmissive optical element 47 are arranged.The radiation source 54 can, for example, be a single radiation source or a combination of several individual radiation sources to provide a substantially continuous radiation spectrum. In modifications, one or more narrowband radiation sources 54 can also be used.

[0073] At least one of the optical elements 27, 28, 30, 31 of the Fig. 8 shown VUV lithography system 21 and at least one of the optical elements 46, 47, 48 of the in Fig. The wafer inspection systems 41 shown in Figure 9 are designed as described above. They are coated with at least one fluoride layer 2, wherein the at least one fluoride layer 2 was deposited according to the method described above and / or by means of the device 1 described above.

[0074] 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 by the excimer laser 62 exits through the laser chamber window 60. The outer side of the laser chamber window 60 is coated with a fluoride layer 2, which was deposited according to the method described above and / or by means of the device 1 described above. The fluoride layer 2 was irradiated with UV / VIS light 10a during the atomic layer deposition to heal potential crystal defects and therefore simultaneously exhibits a high density and a low extinction coefficient. Sealing with such a layer 2 counteracts degradation of the laser chamber window 60 and thus extends its service life. 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] DE 10 2021 201 477 A1

[0004] US 2023 / 0123796 A1

[0007] DE 10 2018 211 499 A1

[0007] WO 2021 / 021436 A1

[0008] WO 2023 / 101862 A1

[0009] US 7 798 096 B2

[0010] US 2005 / 0148206 A1

[0011] US 2017 / 0058401 A1

[0012] DE 10 2021 203 505 A1 [0020, 0027, 0053] Cited non-patent literature

[0000] Photo-Assisted ALD: Process Development and Application Perspectives”, V. Miikkulainen, 2017 ECS Trans. 80 49

[0013] Atomic layer deposition of aluminum fluoride using Al(CH3)3 and SF6 plasma“, M.F.J. Vos et al., Applied Physics Letters 111, 113105 (2017

[0014]

Claims

[1] Method for depositing at least one fluoride layer (2), comprising: Depositing the fluoride layer (2) on a substrate (3) by atomic layer deposition, ALD, in a plurality of ALD cycles (Z), characterized by Irradiating the fluoride layer (2) with UV / VIS light (10a) at least in a part of the plurality of ALD cycles (Z), in particular in all ALD cycles (Z), in order to heal at least one potential crystal defect of the fluoride layer (2). [2] Method according to claim 1, wherein in a first reaction step (A) of a respective ALD cycle (Z) the fluoride layer (2) is exposed to a metallic precursor (MP), wherein preferably the fluoride layer (2) is not irradiated with UV / VIS light (10a) in the first reaction step (A) in order to heal the at least one potential crystal defect. [3] Process according to claim 2, wherein the metallic precursor (MP) is selected from the group comprising: Al(CH3)3, AlCl3, (C2H5)3Al, Mg(thd)2, Mg(EtCp)2, Ca(thd)2, La(thd)2 and LiHMDS. [4] Method according to one of the preceding claims, in which the irradiation of the fluoride layer (2) with the UV / VIS light (10a) in order to heal the at least one potential crystal defect takes place during and / or after a second reaction step (B) of a respective ALD cycle (Z) in which the fluoride layer (2) is exposed to a reactive fluorine precursor (FP). [5] A method according to claim 4, wherein the reactive fluorine precursor (FP) is produced by plasma generation from a fluorination agent (FW). [6] A method according to claim 4 or 5, wherein the reactive fluorine precursor (FP) is produced by photodissociation from a fluorination agent (FW). [7] Process according to one of claims 5 or 6, wherein the fluorinating agent (FW) is selected from the group comprising: SF6, NF3, HF, HF-pyridine, F2, NH4F, CF4, CHF3, TiF4, WF6, MoF5, TaF5. [8] Method according to one of the preceding claims, in which the fluoride layer (2) is irradiated with UV / VIS light (10a) in a first spectral range to heal the at least one potential crystal defect, wherein the fluoride layer (2) is preferably irradiated with UV / VIS light (10b) in a second spectral range to mobilise atoms on its surface (2a). [9] Method according to claim 8, in which at least two fluoride layers (2) with different metallic components are deposited on the substrate (3), wherein the first spectral range is adapted to the respective metallic component of the fluoride layer (2) when irradiating a respective fluoride layer (2). [10] Method according to one of the preceding claims, 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 depositing the at least one fluoride layer (2). [11] The method of claim 10, further comprising: Removal of an aluminum oxyhydroxide layer from the aluminum layer by atomic layer etching in the ALD chamber (4). [12] The method of claim 10, further comprising: Converting an aluminum oxyhydroxide layer formed on the aluminum layer into an aluminum fluoride layer by fluorinating the aluminum oxyhydroxide layer in the ALD chamber (4). [13] Device (1) for atomic layer deposition of at least one fluoride layer (2), comprising - an ALD chamber (4) with a holder (5) for a substrate (3), - a gas supply device (7) for supplying a fluorination agent (FW) into the ALD chamber (4), characterized by that the device (1) comprises at least one UV / VIS light source (9a) for irradiating the fluoride layer (2) with UV / VIS light (10a) in order to heal at least one potential crystal defect of the fluoride layer (2). [14] The device of claim 13, further comprising: an activation device (8) for generating a reactive fluorine precursor (FP) from the fluorination agent (FW), which has a plasma source (11) and / or a UV / VIS light source (9c) for photodissociation of the fluorination agent (FW). [15] Optical element (27, 28, 30, 31; 46, 47, 48; 60) for reflection and / or transmission of radiation (25, 55) in the VUV wavelength range, comprising: a substrate (3) coated with a fluoride layer (2), characterized by , that the fluoride layer (2) was deposited by a method according to one of claims 1 to 12 and / or by means of a device (1) according to one of claims 13 or 14. [16] Optical arrangement for the VUV wavelength range, in particular VUV lithography system (21) or wafer inspection system (41), comprising at least one optical element (27, 28, 30, 31; 46, 47, 48; 60) according to claim 15.

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