Method and apparatus for atomic layer deposition of fluoride layers, 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 photo-assisted atomic layer deposition, i.e. ALD, in a plurality of ALD cycles. The method comprises irradiating the fluoride layer (2) with UV / VIS light (10a) at least in part of the plurality of ALD cycles, in particular in all ALD cycles, in order to repair at least one potential crystal defect of the fluoride layer (2). The invention also relates to a device (1) for atomic layer deposition of at least one fluoride layer (2), to an optical element having a substrate (3) coated with such a fluoride layer (2), and to an optical arrangement having at least one such optical element.

Description

Technical Field

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

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

[0003] Optical components with at least one fluoride layer are commonly used in such systems. For example, highly reflective optical components for use in the VUV wavelength range often have a fluoride layer to protect the underlying metal layer, which reflects the radiation, from oxidation. Layer stacks composed of different fluorides, or of fluorides and optionally oxides, can also be used for reflective or antireflective coatings on optical components. However, the high radiation intensities required in wafer or mask inspection systems and projection exposure equipment often lead to degradation of the fluoride and the optical components, shortening their service life.

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

[0005] This degradation can also be counteracted by a high-density fluoride layer. High-density fluoride layers can generally be deposited by physical vapor deposition (PVD), for example by sputtering. Chemical vapor deposition (CVD), in particular atomic layer deposition (ALD), is a particularly promising technique for depositing fluoride layers or, in general, layers for optical components.

[0006] In atomic layer deposition, multiple ALD cycles are performed sequentially, with one or more coating layers deposited in each ALD cycle. An ALD cycle consists of two or more reaction steps, each of which undergoes a self-terminating surface reaction. Typically, in an ALD cycle, a first sub-reaction with a first precursor occurs in the first reaction step, followed by a second sub-reaction with a second precursor, also referred to as a co-reactant, to reactivate the surface for the first reaction step. A rinse step is typically performed between each reaction step.

[0007] Atomic layer deposition for depositing layers on optical elements is described in the literature primarily in the following documents:

[0008] US 2023 / 0123796 A1 describes an optical element 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.

[0009] WO 2021 / 021436 A1 describes an atomic layer deposition method for coating an optical lens with a magnesium fluoride layer, in which method a magnesium oxide layer is first formed and subsequently converted into a magnesium fluoride layer.

[0010] WO 2023 / 101862 A1 describes a protective coating for aluminum mirrors. To produce this protective coating, an aluminum layer is deposited on a glass substrate using a physical deposition process. First and second fluorine-containing layers, such as MgF2 layers or AlF3 layers, are deposited on the aluminum layer using a physical deposition process. Finally, a third fluorine-containing layer is deposited on the second fluorine-containing layer using an atomic layer deposition process. Prior to depositing the first fluorine-containing layer, the native aluminum oxide layer can be removed from the aluminum layer surface using an atomic layer etching process.

[0011] Thermal ALD processes are generally unattractive due to the elevated temperatures involved in coating optical components, but light-assisted or plasma-based ALD processes are particularly promising:

[0012] US Pat. No. 7,798,096 B2 describes the use of UV light to assist the deposition of high-K dielectrics by chemical vapor deposition or atomic layer deposition. Here, UV light is used to excite or ionize the process gas and to initiate or enhance surface reactions during the deposition process.

[0013] US 2005 / 0148206 A1 describes an ALD process in which a layer is supplied with electromagnetic radiation during or after its exposure to a second reactant in order to destabilize undesirable bonds, in particular metal-metal bonds, by excitation and convert them into the desired bond form.

[0014] US 2017 / 0058401 A1 describes a light-assisted metal ALD process, in which light is used to dissociate a precursor. To dissociate the precursor as efficiently as possible, different wavelengths can be provided.

[0015] In the article "Photo-Assisted ALD: Process Development and Application Perspectives" (V. Miikkulainen, 2017 ECS Trans. 80 49), photo-assisted ALD can simplify the so-called area-selective ALD and introduces photo-assisted ALD processes for metal oxides and metals, in which D2 lamps are mainly used.

[0016] 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 dense AlF3 layers at temperatures between 50°C and 300°C using trimethylaluminum (Al(CH3)3) as a precursor and SF6 plasma as a co-reactant. The extinction coefficients of the deposited AlF3 layers are given in this article and in its "Supplementary Material." The extinction coefficients given there for the VUV wavelength range are relatively large and increase with decreasing deposition temperature, resulting in lower optical properties of the deposited AlF3 layers. The article speculates that the higher extinction coefficient at a deposition temperature of 50°C is due to the high proportion of sulfur in the environment. Summary of the Invention

[0017] The technical problem to be solved by the present invention is to provide a method and an apparatus for atomic layer deposition of a fluoride layer with high optical properties, as well as an optical element and an optical arrangement having such an optical element.

[0018] According to a first aspect, the technical problem is solved by a method of the type mentioned at the outset, comprising the additional step of irradiating the fluoride layer with UV / VIS light at least in a portion of a plurality of ALD cycles, in particular in all ALD cycles, in order to repair at least one latent crystal defect of the fluoride layer. The fluoride layer is typically a metal fluoride layer.

[0019] The inventors have recognized that a disadvantage of light-assisted ALD processes and plasma ALD processes is that, during the coating process, the deposited fluoride layer is exposed to high-energy photons in the UV and VUV wavelength ranges. This high-energy light often leads to the formation of defects (e.g., color centers) in the fluoride layer. These defects can also occur in the bulk of the growing layer and negatively impact the optical properties, i.e., the absorption in the useful wavelength range, here the VUV wavelength range, and the lifetime of the optical element. These defects arise particularly at relatively low deposition temperatures and are the actual cause of the high extinction coefficient described in the above-cited article by MFJVos.

[0020] To address the technical conflict between the ideal low deposition temperature and defect-free solid growth in an ALD process, the present inventors propose providing additional light in an ALD process, particularly in a light-assisted ALD process or a plasma ALD process, to repair crystal defects that typically or potentially occur. Irradiation with UV / VIS radiation to repair crystal defects that typically or potentially occur during fluoride layer deposition can be performed during every ALD cycle, but it is also feasible to perform irradiation only during a portion of the ALD cycles, for example, once every second, third, fourth, and so on ALD cycles, as long as this is sufficient to repair potential crystal defects in the fluoride layer volume.

[0021] For the purposes of the present application, UV light is understood to be electromagnetic radiation in the wavelength range between 100 nm and 380 nm. For the purposes of the present application, VIS light is understood to be radiation in the wavelength range between 380 nm and 830 nm. For the purposes of the present application, UV / VIS light is understood to be radiation in the 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 is generally not carried out over the entire UV / VIS wavelength range, but rather within one or more selected spectral ranges that are adapted to the respective crystal defects to be repaired, in particular in the form of color centers, such as F centers. For example, if the UV / VIS light is generated by a laser source, such as an excimer laser, the corresponding spectral range may optionally include only a single wavelength.

[0022] A suitable wavelength can be selected, for example, in the manner described in DE 10 2021 203 505 A1, which is incorporated herein by reference in its entirety. This document describes the deposition of a layer consisting of an ionically bonded solid on a substrate by transferring a coating material into a gas phase and depositing the transferred coating material onto the substrate, wherein, during the deposition process, the layer is irradiated with UV / VIS light in a first spectral range that at least partially overlaps with the absorption range of at least one (potential) crystal defect, in order to instantaneously repair (potential) crystal defects that arise during the deposition of the coating material.

[0023] In one variant of the method according to the invention, the fluoride layer is exposed to a metal precursor in the first reaction step of the corresponding ALD cycle, wherein preferably, the fluoride layer is not irradiated with UV / VIS light in the first reaction step to repair the at least one latent crystal defect. The deposited fluoride layer is typically a metal fluoride layer deposited with the aid of a metal precursor. Irradiation with UV / VIS light in the first reaction step to repair latent crystal defects is generally disadvantageous, primarily because the metal precursor may be excited or dissociated in an undesirable manner by the UV / VIS light, thereby adversely affecting the formation of the layer.

[0024] In an extended design of this variant, the metal precursor is selected from the group consisting of: 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 type of fluoride layer to be deposited in the ALD process. For example, in the case of an AlF3 layer, Al(CH3)3, i.e., trimethylaluminum (TMA); AlCl3, i.e., trichloroaluminum; or (C2H5)3Al, i.e., triethylaluminum, can be used. In the case of an MgF2 layer, Mg(thd)2 or Mg(EtCp)2 can be used, where "thd" stands for 2,2,6,6-tetramethyl-3,5-heptanedione and "EtCp" stands for ethylcyclopentadiene. For the CaF2 layer, for example, Ca(thd)2 can be used as a metal precursor; for the LaF3 layer, for example, La(thd)2 can be used as a metal precursor; and for the LiF layer, for example, LiHMDS, ie, lithium hexamethyldisilazide, can be used as a metal precursor.

[0025] In another variant, the irradiation of the fluoride layer with UV / VIS light to repair at least one latent crystal defect is performed during and / or after the second reaction step of the corresponding ALD cycle, in which the fluoride layer is exposed to an active fluorine precursor. In this variant, the active fluorine precursor is typically generated by exciting a fluorinating agent, wherein the excitation can be achieved by plasma or electromagnetic radiation, i.e. light. The inventors have recognized that it is advantageous to irradiate with UV / VIS light to repair at least one latent crystal defect (also called "bleaching") during the second reaction step or in a separate bleaching step after the second reaction step. If bleaching is performed in a separate bleaching step, it may be advantageous to also expose the fluoride layer to a fluorinating agent in an additional bleaching step.

[0026] In an extension of this variant, the active fluorine precursor is generated from a fluorinating agent by means of a plasma. The atomic layer deposition process can be carried out, for example, as described in the article cited at the outset by MFJ Vos et al., which is incorporated herein by reference in its entirety. In the ALD process described in this article, SF6 gas is used as the fluorinating agent, and an inductively coupled plasma is generated from the SF6 gas in a plasma source, which plasma contains, for example, F, F2, SF4 and SF 5+ ions and F - Ions serve as active fluorine precursors or active fluorine species. It is also described there that other fluorinating agents, such as HF or HF pyridine, can also be used in the plasma ALD process.

[0027] In another variation, the active fluorine precursor is generated from the fluorinating agent by photolysis. In this variation, the fluorinating agent is irradiated with light, typically UV / VUV light, having at least one wavelength with an energy at least comparable to the dissociation energy of the fluorinating agent. For example, a deuterium lamp can be used as the light source for the photolysis, which emits light in a wavelength range of about 115 nm to about 800 nm almost continuously.

[0028] In another embodiment, the fluorinating agent is selected from the group consisting of SF6, NF3, HF, HF-pyridine, F2, NH4F, CF4, CHF3, TiF4, WF6, MoF5, and TaF5. As described above, the fluorinating agent, which is usually present in the gas phase, can be activated by photolysis or plasma formation, i.e., converted into an active fluorine precursor, thereby enabling the second (sub)reaction step of the corresponding ALD cycle to be performed on the surface of the fluoride layer. As described above, it may be advantageous to irradiate with UV / VIS light in a separate bleaching step, as an alternative or in addition to irradiation in the second reaction step, in which the fluoride layer is exposed to the fluorinating agent without being activated.

[0029] In a further variant, the method comprises irradiating the fluoride layer with light in a third spectral range in order to photolyze the fluorinating agent, wherein the third spectral range lies in a useful wavelength range of the optical element formed during deposition of the fluoride layer, in particular in the VUV wavelength range.

[0030] In this variant, the fluoride layer is irradiated with light in a third spectral range to photolyze the fluorinating agent. It has proven advantageous if the third spectral range lies within the useful wavelength range of the optical component, for example, within the VUV wavelength range. The third spectral range may optionally encompass only a single wavelength, but it can also encompass a broader spectral range. In this case, a deuterium lamp can also be used as the light source for the photolysis, with wavelengths outside the useful wavelength range, for example, wavelengths exceeding 190 nm, being suppressed by optical filtering. The use of the third spectral range within the useful wavelength range of the optical component has the advantage that, in this case, no or only minimal energy is input into the substrate of the optical component during the deposition of the fluoride layer.

[0031] In another embodiment, the fluoride layer is irradiated with UV / VIS light within a first spectral range to repair at least one latent crystal defect, while the fluoride layer is irradiated with light within a second spectral range, preferably for mobilizing atoms on the surface of the fluoride layer. As described above and in DE 10 2021 203 505 A1, the first spectral range or suitable wavelength for repairing latent crystal defects depends on the absorption energy of the crystal defect or the distance between cations and anions 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 a MgF2 or LaF3 layer, the first spectral range can be at or near a central wavelength of 260 nm. As also described in DE 10 2021 203 505 A1, the fluoride layer can also be irradiated with UV / VIS light within a second spectral range to mobilize atoms on its surface. The second spectral range can, for example, be between 75% and 100%, preferably between 80% and 95%, of the band gap energy of the fluoride layer. The wavelength of the second spectral range can be in particular between 115 nm and 122 nm.

[0032] In a further development of this variant, the wavelength of the first spectral range exceeds 190 nm. It has proven advantageous to use UV / VIS light having a wavelength of the first spectral range exceeding 190 nm for repairing crystal defects.

[0033] In a further development of this variant, at least two fluoride layers having different metal compositions are deposited on the substrate, wherein, when irradiating the respective fluoride layer, the first spectral range is adapted to the respective metal composition of the fluoride layer. As described above, the first spectral range for repairing at least one latent crystal defect can be selected or adapted depending on the metal composition of the fluoride layer, which in this example is a metal fluoride layer. Of course, more than two fluoride layers, in particular a stack consisting of more than two fluoride layers, can also be deposited in this manner.

[0034] In another variant, the method further comprises depositing a metal layer, in particular an aluminum layer, on the substrate before introducing the substrate into the ALD chamber for depositing the at least one fluoride layer. In this case, the metal or aluminum layer is deposited outside the ALD chamber by an external deposition process that is not atomic layer deposition, for example by thermal evaporation. It is also possible to deposit one or more additional fluoride layers externally, i.e., before introducing the substrate into the ALD chamber. These fluoride layers can also be deposited by deposition processes other than atomic layer deposition.

[0035] In an extended design of this variant, the method includes removing the aluminum oxyhydroxide layer from the aluminum layer deposited on the substrate by atomic layer etching in an ALD chamber. During the external deposition of the aluminum layer, an aluminum oxyhydroxide layer, typically about 3 nm thick, is formed on the surface of the aluminum layer. x O y layer or more generally form an Al x O y OH z In order to remove the Al x O y OH z Before depositing at least one fluoride layer by atomic layer deposition, an atomic layer etching process can be performed in an ALD chamber. In the atomic layer etching process, individual atomic layers are cyclically removed in two separate, self-limiting sub-reactions, similar to the atomic layer deposition process. For this purpose, suitable reaction gases can be used in both sub-reactions or reaction steps.

[0036] In an alternative embodiment, 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. Fluorination typically involves using one of the aforementioned fluorinating agents, which is converted into an active fluorine species by photolysis or plasma, as described above with respect to the ALD process. After conversion to the aluminum fluoride layer, at least one fluoride layer can be deposited by atomic layer deposition on the substrate or on the aluminum fluoride layer produced by the conversion, in the manner described above.

[0037] In principle, it is possible that the fluorination described above with respect to the aluminum oxyhydroxide layer can also be carried out in an ALD chamber on a fluoride layer deposited by atomic layer deposition in order to supplement or refluorinate the deposited fluoride layer. This can be advantageous, for example, if an oxygen fluoride / hydrogen fluoride layer has formed on the surface of the fluoride layer. For fluorination, the surface of the fluoride layer is exposed to a fluorinating agent. The fluorinating agent is typically converted into an active fluorine species that causes refluorination of the fluoride layer by photolysis using UV / VIS radiation or by plasma.

[0038] The substrate may be heated during the ALD process in the ALD chamber, at least during a portion of the plurality of ALD cycles and / or during refluorination.

[0039] A further aspect of the invention relates to an apparatus for atomic layer deposition of the type mentioned at the outset, further comprising at least one UV / VIS light source for irradiating the fluoride layer with UV / VIS light in order to repair at least one latent crystal defect of the fluoride layer.

[0040] With regard to the advantages achieved by the apparatus described below and its embodiments, reference should be made to the above explanations 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 that the light source is designed to emit both UV light and VIS light.

[0041] At least one UV / VIS light source can be spectrally tunable. Tunable UV / VIS light sources are particularly well-suited for this application because their spectra can be easily adapted to different potential crystal defects and different materials. Suitable tunable UV / VIS light sources are, for example, broadband sources that enable downstream wavelength selection. For example, a D2 gas discharge lamp with downstream wavelength selection can be used for the UV light. Plasma light sources can also be used for this purpose.

[0042] The ALD chamber can be hermetically sealed. The inside of the ALD chamber is resistant to fluorinating agents or active fluorine precursors and their by-products. By-products of fluorinating agents are understood to be fluorine species and compounds formed thereof (such as HF). Resistance should be understood in particular in the sense of a passivation layer formed on the inside of the ALD chamber. In particular, volatile fluorine compounds that may be deposited on optical elements or substrates cannot be formed. The ALD chamber, in particular its inside, can for example be at least partially made of a metal material, which should generally not contain chromium and titanium in order to prevent corrosion. The ALD chamber can in particular be made of monel metal. The inside of the ALD chamber can also have a fluorine-resistant coating to prevent corrosion. This coating is preferably applied by an electroplating process. Suitable materials include NiP, Pt, Ni, Cu or a Ru / Rh mixture. If the device has a plasma source (see below), W, Si and Cr-containing metals should in particular not be used in the ALD chamber.

[0043] In one embodiment, the apparatus includes an activation device for generating a reactive fluorine precursor from a fluorinating agent, the activation device comprising a plasma source and / or a UV / VIS light source for photolyzing the fluorinating agent. 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 by the fluorinating agent. To this end, the fluorinating agent can be delivered to a plasma source and / or irradiated by a UV / VIS light source that generates UV / VIS light having an energy that is at least as great as the dissociation energy of the fluorinating agent.

[0044] Of course, the apparatus may also include further components typical of ALD apparatuses, such as metering devices for metal precursors (including valves and mixing taps), metering devices for fluorinating agents (including valves and mixing taps), metering devices for purge gases or inert gases, vacuum technology for generating a vacuum in the ALD chamber, vacuum locks, etc. In particular, the apparatus may also include shielding for plasma shielding and / or plasma shaping. It is also advantageous if the apparatus includes devices for optically monitoring the ALD process, for example, by in-situ ellipsometry. If a plasma source is used to generate the active fluorine precursor, the ALD chamber may also include a sensor system for monitoring the plasma of the plasma source.

[0045] A further aspect of the present invention relates to an optical element of the type described in the introduction, wherein the fluoride layer has been deposited according to the above-described method and / or by means of the above-described apparatus. Of course, the optical element may also have two or more fluoride layers, which have been deposited by the ALD process described above or by means of corresponding apparatus. The optical element may also include one or more fluoride layers or other layers not deposited by atomic layer deposition, such as metal layers.

[0046] 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 for deflecting or focusing radiation in the VUV wavelength range, or a beam splitter for both transmitting and reflecting radiation in the VUV wavelength range.

[0047] A further aspect of the present invention relates to an optical arrangement 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 arrangement may be, for example, a (VUV) lithography system, a wafer or mask inspection system, a laser system, or the like.

[0048] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention and from the claims, with reference to the accompanying drawings which show essential details of the invention. The individual features can be implemented individually or in any combination in a variant of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Some exemplary embodiments are shown in the schematic drawings and are explained in the following description.

[0050] Figure 1 A schematic diagram of an apparatus for atomic layer deposition of a fluoride layer on a substrate is shown, the apparatus having two UV light sources for emitting UV light and an excitation device for exciting a fluorinating agent;

[0051] Figure 2 Shown in Figure 1 A flow chart of an ALD process for depositing a fluoride layer on a substrate in an apparatus;

[0052] Figure 3a 、 Figure 3b Flowchart showing two variations of a photo-ALD process for depositing a fluoride layer;

[0053] Figure 4a 、 Figure 4b Flowchart showing two variations of a plasma ALD process for depositing a fluoride layer;

[0054] Figure 5 A flow chart showing a coating process for an optical element in which a further layer is deposited in addition to the fluoride layer deposited in the ALD process;

[0055] Figure 6 A flow chart showing a coating process in which an oxyhydroxide layer is removed in an ALD chamber prior to depositing a fluoride layer;

[0056] Figure 7 A flow chart showing an ALD process for depositing multiple different fluoride layers;

[0057] Figure 8 Schematic diagram showing an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus;

[0058] Figure 9 A schematic diagram showing an optical arrangement for the VUV wavelength range in the form of a wafer inspection system; and

[0059] Figure 10 Schematic diagram showing optical elements in the form of laser chamber windows.

[0060] In the following description of the figures, the same reference numerals are used for identical or functionally identical components. DETAILED DESCRIPTION

[0061] Figure 1 An apparatus 1 for atomic layer deposition of one or more fluoride layers 2 on a substrate 3 is shown. For this purpose, the apparatus 1 comprises an ALD chamber 4 in the form of a vacuum chamber, in which a support 5 (manipulator) for the substrate 3 is mounted in the form of a turntable. An electrical potential (bias) can be applied to the support 5, for example, in order to accelerate ions from a plasma toward the substrate 3. The support 5 can also be heated by means of a heating device (not shown in the figure). A vacuum pump 6 is used to generate a vacuum in the interior of the ALD chamber 4.

[0062] Apparatus 1 further comprises a gas delivery device 7, which is designed to feed a gaseous fluorinating agent FW, a gaseous metal precursor MP, and a purge or inert gas IG into the ALD chamber 4 and has a plurality of gas inlets for this purpose. Gas delivery device 7 further comprises a valve or metering arrangement that enables controlled feeding of the gaseous fluorinating agent FW, the gaseous metal precursor MP, and the inert gas IG into the interior of the ALD chamber 4. The fluorinating agent FW can also be fed to an activation device 8, through which it enters the interior of the ALD chamber 4, as described in detail below.

[0063] The metal precursor MP delivered from a gas tank 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 fluorinating agent FW is selected based on the metal component of the fluoride layer 2, which in the example shown is a metal fluoride layer. The fluorinating agent FW described here is suitable for depositing the fluoride layer 2 in the form of an AlF3 layer, a MgF2 layer, or a LaF3 layer in an ALD process. In the example shown, trimethylaluminum, i.e., Al(CH3)3, is used as the metal precursor MP.

[0064] For example, the inert gas IG may be a rare gas, such as argon, which can be used primarily to ventilate the ALD chamber 4 before opening, to set the pressure of the interior of the ALD chamber 4, and in particular to serve as a flushing gas for flushing the interior of the ALD chamber 4 between reaction steps A and B of the ALD process, see Figure 2 .

[0065] For example, the fluorinating agent FW can be SF6, NF3, HF, HF-pyridine, F2, NH4F, CF4, CHF3, TiF4, WF6, MoF5, or TaF5. In the illustrated example, gaseous SF6 is used as the fluorinating agent. To carry out the (sub)reaction step of the ALD process, it is necessary to generate an active fluorine precursor FP from the fluorinating agent FW and expose the surface of the fluoride layer 2 or substrate 3 to this active fluorine precursor. An activation device 8 is used for this purpose.

[0066] to this end, Figure 1 The activation device 8 shown in the figure has a (third) light source 9c in the form of a photolysis light source for photolysis of the fluorinating agent FW and a plasma source 11. When the fluorinating agent FW is activated by the UV light source 9c, the fluorinating agent is directly introduced into the inner space of the ALD chamber 4 through the gas inlet of the gas conveying device 7. In this case, the activation is achieved by photolyzing the fluorinating agent FW with the light 10c generated by the third light source 9c. The light 10c generated by the third light source 9c has at least one wavelength whose photon energy is greater than the dissociation energy of the fluorinating agent FW. Therefore, the third light source 9c or the light 10c generated by it is adapted to the fluorinating agent FW used. In the example shown, the light 10c of the third light source 9c is irradiated onto the fluoride layer 2. The light 10c of the third light source 9c is light 10c in a third spectral range, which is within the useful wavelength range of the optical element formed when the fluoride layer 2 is deposited on the substrate 3. In the example shown, the third spectral range is within the VUV wavelength range.

[0067] When generating the active fluorine precursor FP from the fluorinating agent FW by forming a plasma, the fluorinating agent FW is supplied to a plasma source 11, which activates the fluorinating agent and forms the active fluorine precursor FP, which may comprise, for example, fluorine radicals or fluorine in an excited electronic state. Of course, the activation device 8 does not necessarily need to include both the plasma source 11 and the photolysis light source 9c: generally, one of these two sources is sufficient to generate the active fluorine precursor FP.

[0068] Figure 1 The device 1 shown also has a first and a second UV light source 9a, 9b for generating UV light 10a, 10b which is irradiated onto the surface 2a of the fluoride layer 2. Figure 1In the example shown, a first UV light source 9a is designed to emit UV light 10a in a first spectral range for repairing potential crystal defects during the deposition of the fluoride layer 2 in an atomic layer deposition process. The wavelength of the first spectral range can be greater than 190 nm. A second UV light source 9b is designed to emit UV light 10b in a second spectral range for mobilizing atoms on the surface 2a of the fluoride layer 2. These two spectral ranges are not shown and are selected depending on the material being deposited, wherein this selection can be made, for example, in the manner described in DE 10 2021 203 505 A1 cited above.

[0069] and Figure 1 Unlike the illustration in FIG, 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 a first UV light source 9a that emits UV light 10a in the first spectral range. The device 1 can also have more than two UV light sources 9a, 9b.

[0070] In the example shown, the first UV light source 9a and the second UV light source 9b are each designed to emit UV light 10a, 10b in a fixedly preset first or second spectral range. However, it is also possible that the first and / or second UV light source 9a, 9b is tunable so that the first and / or second spectral range can be set or tuned. Figure 1 In the example shown, 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 that mainly generates light in the wavelength range of 115-122 nm.

[0071] Alternatively, one or both light sources 9a, 9b can be designed to generate light in the visible wavelength range (VIS light). In this case, light sources 9a, 9b can be designed to emit VIS light within a predetermined first or second spectral range, or light sources 9a, 9b can be tunable. It is also possible for a single VIS light source to generate VIS light within both the first and second spectral ranges. Alternatively, one or more UV light sources and one or more VIS light sources can be provided.

[0072] The following reference Figure 2 The flowchart shown is described in Figure 1The invention relates to an atomic layer deposition process for a fluoride layer, more specifically an AlF3 layer, in an apparatus 1 of the present invention. In the method, in a first step, a substrate 3, such as a glass substrate or a substrate in the form of a crystal, is fastened to a holder 5, a flushing step is performed, and the ALD chamber 4 is evacuated. Subsequently, the first (sub) reaction step A of the ALD cycle Z is performed, in which the surface of the deposited portion of the substrate 3 or the fluoride layer 2 is exposed to the metal precursor MP, and the first surface reaction of the ALD process is performed on the surface of the fluoride layer 2. In the subsequent flushing step, the residues of the metal precursor MP and the volatile reaction products of the first reaction step A are evacuated from the inner space of the ALD chamber 4, and after this flushing step, the second (sub) reaction step B of the ALD cycle Z is performed.

[0073] In the second reaction step B, the surface 2a of the fluoride layer 2 is exposed to an active fluorine precursor FP. Figure 1 The described method is to generate the fluoriding agent FW, which in the example shown is SF6, either by photolysis or by plasma formation. The surface reactions that take place in two reaction steps A and B are described in the article by MFJ Vos et al. cited at the outset. The two reaction steps A and B and the respective subsequent rinsing steps constitute an ALD cycle Z, in which one or more AlF3 layers are deposited. The ALD cycle Z is repeated n times until the fluoride layer 2 has a predetermined thickness. Depending on the thickness of the fluoride layer 2, the number n of ALD cycles Z can be between approximately 10 and 500. After the fluoride layer 2 has grown to the desired thickness, the substrate 3 is removed from the ALD chamber 4.

[0074] from Figure 2 It can also be seen that in the second reaction step B, the surface 2a of the substrate 3 or the fluoride layer 2 is exposed to UV light 10a of the first UV light source 9a in order to repair at least one latent crystal defect of the fluoride layer 2, as described above with respect to Figure 1 As described.

[0075] Figure 3a 、 Figure 3b Two variants of the photo-ALD process for depositing the fluoride layer 2 are shown, wherein: Figure 3a The first variant shown is similar to Figure 2 The variant shown corresponds to the embodiment in which the activation of the fluorinating agent FW is carried out by photolysis. Figure 3b In the variant shown, in addition to irradiating the fluoride layer 2 with UV light 10 a in the second reaction step B, a bleaching step is performed in a further subsequent process step of the corresponding ALD cycle Z, in which the surface 2 a of the fluoride layer 2 is also irradiated with UV light 10 a in order to repair potential crystal defects in the fluoride layer 2. Alternatively, bleaching can be performed only after the second reaction step B. Figure 3b As shown, a fluorinating agent FW may be added to the inner space of the ALD chamber 4 during the bleaching step to cause refluorination of the fluoride layer 2 , for example, when a layer composed of oxyfluoride / hydrogen fluoride has been formed on the surface 2 a of the fluoride layer 2 .

[0076] Figure 4a 、 Figure 4b Two variants of the plasma ALD process for depositing the fluoride layer 2 are shown, wherein Figure 4a The first variant shown is similar to Figure 2 The variant shown corresponds to the one in which the activation of the fluorinating agent FW is carried out by plasma or plasma cleavage to form the active fluorine precursor FP. Figure 4b In, with Figure 3b Similarly, 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. Figure 3b The difference is that in Figure 4b In the variant shown, no bleaching is carried out during the second reaction step B. However, Figure 4b Bleaching can also be performed in the plasma ALD process described in .

[0077] To produce an optical element, generally not only the fluoride layer 2 but also further layers are deposited on the substrate 3 . Figure 5 The flow chart shows a method in which, in two preceding steps, first an aluminum layer and then a fluoride layer or fluoride coating are deposited on a substrate 3, after which 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 aluminum layer and the fluoride layer are not deposited by atomic layer deposition before introduction into the ALD chamber 4, but rather, for example, by a thermal evaporation process.

[0078] Figure 6 Shown with Figure 5 A similar process flow is used in which a native thin Al layer is formed on the surface of the aluminum layer after the aluminum layer is deposited in ambient air. x O y layer or more generally form Al x O y OH z In order to remove the Al x O y OH z Before depositing at least one fluoride layer 2 by an atomic layer deposition process, an atomic layer etching process ( Figure 6 In this case, the device 1 is designed not only for atomic layer deposition but also for atomic layer etching.

[0079] Alternatively, Al x O y OH z The layer is removed from the surface of the aluminum oxide layer by x O y OH z layer into an aluminum fluoride layer ( Figure 6 For this conversion, a fluorinating agent FW is used, to which the surface of the aluminum layer is exposed, and active fluorine species are generated from the fluorinating agent by photolysis or plasma, as described above for the ALD process. After the conversion to the aluminum fluoride layer, at least one fluoride layer 2 can be deposited by atomic layer deposition in the manner described above on the substrate 3, more precisely on the aluminum fluoride layer produced by the conversion.

[0080] The fluorination described above with respect to the aluminum oxyhydroxide layer can also be performed in the ALD chamber 4 on a fluoride layer deposited by atomic layer deposition to supplement or refluorinate the deposited fluoride layer 2. This can be advantageous, for example, if an oxygen fluoride / hydrogen fluoride layer is formed on the surface of the fluoride layer 2. To perform the fluorination, the surface 2a of the fluoride layer 2 is exposed to a fluorinating agent FW. The fluorinating agent is typically photolyzed using UV / VIS light 10c or converted by plasma into an active fluorine species that causes refluorination of the fluoride layer 2.

[0081] Figure 7 The method flow for depositing multiple dielectric functional fluoride layers is shown. These fluoride layers are applied alternately on a substrate 3 to produce a functional coating, such as a reflective or antireflective dielectric coating. In the illustrated example, the coating comprises n alternating layers of AlF3 and LaF3. During the deposition of the respective fluoride layer 2, the spectral range of the UV light 10a emitted by the bleaching light, more precisely, the first UV light source 9a, is adapted to the metallic material to be deposited on the fluoride layer 2. More precisely, in the illustrated example, the first spectral range is switched from the wavelength range of approximately 170 nm to 190 nm used for AlF3 atomic layer deposition to a wavelength of approximately 260 nm used for MgF2 atomic layer deposition.

[0082] Figure 8 An optical arrangement for the VUV wavelength range is shown 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 also has a radiation source 24, which may be, for example, an excimer laser.

[0083] Radiation 25 emitted by radiation source 24 is processed by means of illumination system 22 so as to illuminate mask 26, also referred to as a reticle. In the example shown, illumination system 22 has a housing 32 in which transmissive and reflective optical elements are arranged. Transmissive optical element 27, which focuses radiation 25, and reflective optical element 28, which deflects radiation, are shown as representative examples.

[0084] Mask 26 has a structure on its surface that is transferred to an optical element 29 to be exposed, such as a wafer, by means of projection system 23 in order to manufacture semiconductor devices. In the example shown, mask 26 is designed as a transmissive optical element. In other embodiments, mask 26 can also be designed as a reflective optical element.

[0085] In the example shown, the projection system 23 has at least one transmissive optical element. In the example shown, two transmissive optical elements 30 , 31 are shown as representatives, for example for reducing the structures on the mask 26 to the size required for exposing the wafer 29 .

[0086] Various transmissive, reflective or other optical elements can be combined with one another in any desired, even complex, manner in the illumination system 22 and the projection system 23. Optical arrangements without transmissive optical elements can also be used for VUV lithography.

[0087] Figure 9 The optical arrangement for the VUV wavelength range is shown in the form of a wafer inspection system 41, but it can also be a mask inspection system. Wafer inspection system 41 has an optical system 42 with a radiation source 54, which directs radiation 55 from the radiation source onto wafer 49 via optical system 42. To this end, radiation 55 is reflected onto wafer 49 by a concave mirror 46. In a mask inspection system, a mask to be inspected can be arranged instead of wafer 49. The radiation reflected, diffracted, and / or refracted by wafer 49 is guided by a further concave mirror 48, also part of optical system 42, via a transmissive optical element 47 to a detector 50 for further evaluation. Wafer inspection system 41 also has a housing 52, in which the two mirrors 46, 48 and the transmissive optical element 47 are mounted. Radiation source 54 can, for example, be just one radiation source or a combination of multiple individual radiation sources to provide a substantially continuous radiation spectrum. In a variant, one or more narrowband radiation sources 54 can also be used.

[0088] Figure 8 At least one of the optical elements 27, 28, 30, 31 of the VUV lithography apparatus 21 and Figure 9At least one of the optical elements 46, 47, 48 of the wafer inspection system 41 shown is designed as described above. That is, it is coated with at least one fluoride layer 2, wherein the at least one fluoride layer 2 has been deposited according to the above-described method and / or by the above-described device 1.

[0089] Figure 10 An optical element for transmitting radiation in the VUV wavelength range is shown in the form of a laser chamber window 60 of a laser chamber 61 housing an excimer laser 62. The laser beam emitted by the excimer laser 62 is transmitted to the outside through the laser chamber window 60. The outer surface of the laser chamber window 60 is coated with a fluoride layer 2, which has been deposited according to the above-described method and / or using the above-described apparatus 1. The fluoride layer 2 has been irradiated with UV / VIS light 10a during atomic layer deposition to repair potential crystal defects and therefore has both a high density and a low extinction coefficient. Sealing with such a layer 2 counteracts degradation of the laser chamber window 60, thereby extending its lifetime.

Claims

1. A method for depositing at least one fluoride layer (2), comprising: Depositing the fluoride layer (2) on a substrate (3) by light-assisted atomic layer deposition, i.e. ALD, in a plurality of ALD cycles (Z), It is characterized by: The fluoride layer (2) is irradiated with UV / VIS light (10a) in at least a portion of the plurality of ALD cycles (Z), in particular in all ALD cycles (Z), so as to repair at least one latent crystal defect of the fluoride layer (2).

2. The method according to claim 1, wherein In a first reaction step (A) of a corresponding ALD cycle (Z), the fluoride layer (2) is exposed to a metal precursor (MP), wherein preferably, the fluoride layer (2) is not irradiated with UV / VIS light (10a) in the first reaction step (A) to repair the at least one latent crystal defect.

3. The method according to claim 2, wherein: The metal precursor (MP) is selected from the following group, which includes: Al(CH3)3, AlCl3, (C2H5)3Al, Mg(thd)2, Mg(EtCp)2, Ca(thd)2, La(thd)2 and LiHMDS.

4. A method according to any one of the preceding claims, wherein Irradiating the fluoride layer (2) with UV / VIS light (10a) to repair the at least one latent crystal defect is performed during and / or after the second reaction step (B) of the corresponding ALD cycle (Z), in which the fluoride layer (2) is exposed to a reactive fluorine precursor (FP).

5. The method according to claim 4, wherein The active fluorine precursor (FP) is generated from the fluorinating agent (FW) by photolysis.

6. The method according to claim 4 or 5, wherein: The fluorinating agent (FW) is selected from the following group, which includes: SF6, NF3, HF, HF-pyridine, F2, NH4F, CF4, CHF3, TiF4, WF6, MoF5, TaF5.

7. The method according to any one of claims 4 to 6, further comprising: The fluoride layer (2) is irradiated with light (10c) in a third spectral range, in order to photolyze the fluorinating agent (FW), wherein the third spectral range lies in the useful wavelength range of an optical element (27, 28, 30, 31; 46, 47, 48; 60) formed during the deposition of the at least one fluoride layer (2), in particular in the VUV wavelength range.

8. A method according to any one of the preceding claims, wherein The fluoride layer (2) is irradiated with UV / VIS light (10a) in a first spectral range in order to repair the at least one latent crystal defect, wherein the fluoride layer (2) is irradiated with light (10b) in a second spectral range, preferably for mobilizing atoms on the surface (2a) of the fluoride layer.

9. The method according to claim 8, wherein The wavelength of the first spectral range exceeds 190 nm.

10. The method according to claim 8 or 9, wherein: At least two fluoride layers (2) having different metal compositions are deposited on the substrate (3), wherein when the respective fluoride layer (2) is irradiated, the first spectral range is adapted to the respective metal composition of the fluoride layer (2).

11. The method according to any one of the preceding claims, further comprising: Before the substrate (3) is introduced into an ALD chamber (4) for depositing the at least one fluoride layer (2), a metal layer, in particular an aluminum layer, is deposited on the substrate (3).

12. The method according to claim 11, further comprising: The aluminum oxyhydroxide layer is removed from the aluminum layer by atomic layer etching in an ALD chamber (4).

13. The method according to claim 11, further comprising: The aluminum oxyhydroxide layer formed on the aluminum layer is converted into an aluminum fluoride layer by fluorinating the aluminum oxyhydroxide layer in an ALD chamber (4).

14. An apparatus (1) for atomic layer deposition of at least one fluoride layer (2), comprising - an ALD chamber (4) having a holder (5) for a substrate (3); - a gas delivery device (7) for feeding the fluorinating agent (FW) into the ALD chamber (4); It is characterized by: The apparatus (1) comprises at least one UV / VIS light source (9a) for irradiating the fluoride layer (2) with UV / VIS light (10a) so as to repair at least one latent crystal defect of the fluoride layer (2).

15. The apparatus according to claim 14, further comprising: An activation device (8) for generating an active fluorine precursor (FP) from the fluorinating agent (FW), the activation device having a UV / VIS light source (9c) for photolyzing the fluorinating agent (FW).

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

17. An optical arrangement 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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