Method and apparatus for depositing at least one layer, optical element, and optical device

Abstract

The invention relates to a method for depositing at least one layer (2) of an ionically bonded solid on a substrate (3), comprising the steps of converting a coating material (8) into the gas phase and depositing the coating material (8) converted into the gas phase on the substrate (3), the layer (2) being irradiated with UV / VIS light (11a, 11b) during deposition. The invention also relates to an apparatus (1) for depositing at least one layer (2) of an ionically bonded solid, comprising a coating chamber (4) having a mount (5) for the substrate (3) and at least one coating source (7) designed to convert the coating material (8) into the gas phase and deposit it in the coating chamber (4) as a layer (2) on the substrate (3). The apparatus (1) comprises one or more UV / VIS light sources (12a, 12b) for irradiating the layer (2) with UV / VIS light (11a, 11b) during deposition. The invention also relates to an optical element coated with at least one above-mentioned layer (2) and to an optical device comprising at least one said optical element.

Description

[Technical Field]

[0001] REFERENCE TO RELATED APPLICATIONS This application claims priority from German Patent Application No. 10 2021 203 505.1 filed on April 9, 2021, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a method for depositing at least one layer of an ionically bonded solid on a substrate, in particular by physical vapor deposition, comprising the steps of converting a coating material into a gas phase and depositing the converted coating material on the substrate. The present invention also relates to an apparatus for depositing at least one layer of an ionically bonded solid, comprising a coating chamber having a mount for the substrate and a coating source designed to convert the coating material into a gas phase and deposit it as a layer on the substrate in the coating chamber. The present invention also relates to an optical element that reflects and / or transmits radiation in the VUV wavelength range, and an optical device for the VUV wavelength range comprising at least one such optical element. [Background technology]

[0003] When the electronegativity difference is 1.7 or greater, the type of bonding is called ionic. Examples of ionically bonded solids are oxides and fluorides containing alkali metal halides and alkaline earth metal halides. The conversion of a coating material into the gas phase and its deposition onto a substrate is characteristic of physical vapor deposition. Corresponding methods include thermal evaporation and electron beam evaporation, sputter deposition, ion beam sputtering, and arc evaporation, all with or without plasma assistance.

[0004] In the present application, the VUV wavelength range is understood to mean the wavelength range of electromagnetic radiation between 115 nm and 190 nm. The VUV wavelength range is particularly important for microlithography. Radiation in the VUV wavelength range is therefore used, for example, in projection exposure apparatus and wafer or mask inspection apparatus.

[0005] Optical elements with ionic solids in the form of at least one fluoride layer or fluoride substrate are often used in such devices. Highly reflective optical elements for the VUV wavelength range usually have, for example, a fluoride layer to protect the underlying metal layer that reflects radiation from oxidation. Stacks of different fluorides or fluorides and oxides can also be used for reflective or anti-reflective coatings of optical elements. However, since most oxides have high absorption in the VUV wavelength range, the scope here is generally limited to a few materials, such as SiO2. Transmitting optical elements for the VUV wavelength range, such as laser chamber windows for excimer lasers, are also based on fluoride substrates.

[0006] However, high radiation intensities, such as those required in wafer or mask inspection and projection exposure systems, generally lead to degradation of fluoride and optical elements, thereby shortening their lifetime. This degradation can be suppressed by a high-density fluoride layer. For example, the exterior of a laser chamber window can be sealed by depositing a high-density fluoride layer.

[0007] Dense layers of ionically bonded solids, such as fluoride layers, can be produced by plasma-assisted deposition, e.g., sputter deposition, e.g., ion beam sputtering (IBS), or plasma-ion-assisted deposition (PIAD) or plasma-enhanced atomic layer deposition (PEALD). However, when depositing ionically bonded solids, including oxides and fluorides, by plasma-assisted deposition, ion bombardment also has the effect of increasing the generation of crystalline defects, e.g., in the form of color centers, resulting in greater quenching compared to, e.g., purely thermally evaporated layers. Furthermore, plasmas also emit UV / VUV radiation. The short-wave portion of this radiation can also generate crystalline defects by single-photon processes, which can adversely affect the optical performance and / or irradiation stability of the deposited layers.

[0008] The literature suggests that the optical performance of plasma- (ion-)assisted deposited fluorides in the deep UV wavelength range can be improved by subsequent irradiation with UV light. For example, Non-Patent Document 1 describes the post-treatment of metal fluoride layers deposited by plasma-assisted electron beam evaporation with UV radiation. According to this paper, the initially low transmittance of LaF3, MgF2, and AlF3 layers in the deep UV wavelength range can be significantly increased by this post-treatment. During this subsequent irradiation, color centers are bleached and unsaturated bonds are presumably (superficially) further oxidized.

[0009] This procedure is practical for oxides in general and for fluorides used in the DUV wavelength range (i.e., wavelengths above 190 nm), but is generally not practical for fluorides in the VUV wavelength range, where oxidation leads to loss of optical performance.

[0010] US Patent No. 6,239,999 describes the use of UV light to assist in the deposition of high-k dielectrics by chemical vapor deposition or atomic layer deposition, where UV light is used to excite or ionize process gases, thereby initiating or amplifying surface reactions during deposition.

[0011] Patent document 2 discloses nanostructuring of a substrate for the transmission of radiation in the FUV / VUV wavelength range by introducing an energy input, for example by irradiation with UV / VUV radiation. In this case, the substrate is crystalline, for example the substrate is a MgF2 single crystal. The irradiation can reorganize the surface of the MgF2 single crystal in such a way that an antireflection effect occurs.

[0012] US Patent No. 5,999,623 discloses a method of operating a microlithography optical device having optical elements with a fluoride coating or made of a fluoride substrate, in which during operation UV light of wavelengths greater than the wavelength of the light used in the optical device, below 300 nm, is irradiated in order to anneal fluoride defects.

[0013] Patent Document 4 discloses a method for producing optical elements for the VUV wavelength range, such as mirrors, windows, or beam splitters, with a coating of a fluorine scavenger layer that can be applied to a fluoride layer. The purpose of the fluorine scavenger layer is to prevent degradation of the fluoride layer, thereby extending the life of the optical element. The underlying mechanism is a significant reduction in the mobility of interstitial fluorine atoms due to the so-called fluorine scavengers in the fluorine scavenger layer.

[0014] Patent document 5 describes the irradiation of a metal fluoride layer with radiation of at least one wavelength less than 300 nm. The metal fluoride layer is applied to a metal layer of a reflective optical element for use in the VUV wavelength range. The irradiation is carried out after application of the coating. The irradiation passivates the metal fluoride layer, which inhibits degradation of the metal layer.

[0015] Patent Document 6 discloses a method for coating a substrate by plasma-assisted deposition of a coating material, such as a fluoride material. The plasma contains ions with a relatively low effective ion energy, but a relatively high effective energy per molecule, which is intended to lead to a high packing density as well as low absorption and contamination of the deposited layer.

[0016] US Pat. No. 5,649,493 discloses a method for ion beam sputtering of metal fluoride layers in the presence of dissociated fluorine gas.

[0017] US Patent Nos. 5,999,023 and 5,999,023 describe further variations on physical vapor deposition of fluoride layers. US Patent No. 5,999,023 discloses a fluorination treatment as a post-treatment of a fluoride layer. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] U.S. Patent No. 7,798,096 [Patent Document 2] DE 10 2018 221 190 [Patent Document 3] German Patent Application No. 102020210195.7 [Patent Document 4] German Patent Application No. 102020208044.5 [Patent Document 5] German Patent Application No. 102021200490.3 [Patent Document 6] DE 10 2005 017 742 A1 [Patent Document 7] US Patent Application Publication No. 2013 / 0122252 [Patent Document 8] Japanese Patent Application Publication No. 11-172421 [Patent Document 9] Japanese Patent Application Laid-Open No. 2003-193231 [Patent Document 10] US Patent Application Publication No. 2004 / 0006249 [Non-patent literature]

[0019] [Non-Patent Document 1] “Plasma-assisted deposition of metal fluoride coatings and modeling the extinction coefficient of as-deposited single layers”, M. Bischoff et al., Appl. Opt. 50, 232-238 (2010) Summary of the Invention [Problem to be solved by the invention]

[0020] Against this background, it is an object of the present invention to provide a method and apparatus for depositing a layer made of an ionically bonded solid, an optical element having high optical performance, and an optical device comprising such an optical element. [Means for solving the problem]

[0021] This object is achieved, according to a first aspect, by a method of the type described above, in which at least one layer is irradiated with UV / VIS light during deposition.

[0022] By irradiating the layer(s) with regenerating UV / VIS light during deposition, crystalline defects that arise during deposition are instantly annealed, resulting in a lower extinction coefficient for the deposited layer(s) compared to deposition without UV / VIS light irradiation, resulting in higher transmittance and longer lifetime for the deposited layer(s) and for substrates or optical elements coated therewith, which is especially important in the case of high radiation intensities in microlithography.

[0023] In contrast, subsequent treatment of crystalline defects has the disadvantage that reoxidation and refluorination generally only occurs superficially, whereas bulk damage caused during the coating process is generally irreversible.

[0024] Within the meaning of the present application, UV light is understood to be electromagnetic radiation in the wavelength range from 100 nm to 380 nm. Within the meaning of the present application, VIS light is understood to be radiation in the wavelength range from 380 nm to 830 nm. Within the meaning of the present application, UV / VIS light is understood to be radiation in the wavelength range from 100 nm to 380 nm (UV light) and / or in the wavelength range from 380 nm to 830 nm (VIS light). The UV / VIS wavelength range can be further limited, for example, to 170 nm to 730 nm. Irradiation with UV / VIS light generally does not take place over the entire UV / VIS wavelength range, but rather in one or more selected spectral ranges. For example, if the UV / VIS light is generated by a laser source, e.g., an excimer laser (see below), each spectral range may in some cases contain only a single wavelength.

[0025] In one variant of the method, the UV / VIS light has a first spectral range that at least partially overlaps the absorption region of at least one crystalline defect in the ionically bonded solid for annealing at least one crystalline defect, the first spectral range preferably including the absorption energy of the crystalline defect, more preferably the mean energy of the first spectral range deviating from the absorption energy of the crystalline defect by at most 0.5 eV, in particular by at most 0.25 eV.

[0026] The absorption energy of a crystal defect is understood to mean the energy or wavelength at which the absorption coefficient of the crystal defect in the ionic solid material is maximum. The absorption region of a crystal defect is understood to mean the region in which the absorption coefficient is greater than half the maximum (FWHM). The absorption energies of the crystal defects of three fluorides relevant to this application are shown below as examples: MgF2: 260 nm (4.77 eV), AlF3: 190 nm (6.53 eV), 170 nm (7.29 eV), LaF3: 459 nm (2.7 eV), 564 nm (2.2 eV), 729 nm (1.7 eV).

[0027] In one development of this variant, the crystal defects form color centers, in particular F-centers. Color centers are crystal defects that absorb in particular visible light. F-centers are particularly simple color centers. In the case of F-centers, an electron occupies the missing anion. Other color centers are, for example, M-centers and R-centers, each consisting of a group of F-centers. As a result of irradiation with UV / VIS light during deposition, electrons are removed from the crystal defects, and thus lattice sites become available for newly arriving atoms and / or anions, for example F-centers. - Or O 2- As a result, deep damage to the layer is instantly suppressed.

[0028] In yet another variation of the method, the first spectral range is selected based on the relationship between the absorption energy of at least one crystal defect and the anion-cation distance of the ionically bonded solid. An example of a corresponding relationship is the Mollwo-Ivey law (see the paper "Uber die Absorptionsspektra photochemisch verfarbter Alkalihalogenid-Cristalle", E. Mollwo, Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, 97-100 (1931) and the paper "Ab initio perspective on the Mollwo-Ivey relation for F centers in alkali halides", P. Tiwald et al., Phys Rev B 92 (2015) 144107).

[0029] The Mollwo-Ivey law was originally established for the F center of alkali metal halides, and it derives the absorption energy E of a crystal defect from the lattice constant a by a simple power law with exponent n and constant C. abs It is said that the following can be obtained. E abs =Ca -n

[0030] Although this law was formulated only for cubic crystalline systems, it can be generalized within certain limits to ionic solids with more complex crystal structures, thus allowing the prediction of the spectral range in which UV / VIS light should be irradiated to anneal crystalline defects. The exponent n and the constant C should be adapted in the process of such generalization.

[0031] In yet another variation of the method, the first spectral range has an average energy greater than 1 eV or less, preferably 1.5 eV or less, than the absorption energy of at least one crystal defect. If the energy of the UV / VIS light is significantly greater than the absorption energy of the crystal defect, typically at least 1 eV or 1.5 eV greater, the generation of additional crystal defects and / or defect conversion will be increased. Therefore, it is advantageous to impose an upper limit on the energy of the first spectral range of UV / VIS light. While a lower limit on the energy or bandwidth of the first spectral range is not necessarily required, using UV / VIS light with too low an energy generally makes it impossible to anneal the crystal defects and should be avoided.

[0032] In yet another variation of the method, the UV / VIS light has a second spectral range for displacing atoms at the surface of the ionically bonded solid, the second spectral range being in an energy range of 75% to 100%, preferably 80% to 95%, of the band gap energy of the ionically bonded solid.

[0033] As described, for example, in the above-cited US Pat. No. 5,949,999, high-energy light near the band edge of ionic solids can move surface atoms or atoms without desorption. Therefore, irradiation with UV / VIS light near the band edge can have the same effect as increasing the temperature in a coating, and its influence on layer growth can be explained, for example, by the so-called structural zone model. The increased surface mobility of atoms can potentially more easily overcome the Ehrlich-Schwobel barrier, resulting in larger grains and fewer grain boundaries, which in turn leads to a smaller extinction coefficient.

[0034] In yet another variant of the method, the average energy of the first and / or second spectral range of UV / VIS light is or has been set to less than 0.5 eV, preferably less than 0.25 eV, and / or the bandwidth of the first and / or second spectral range of UV / VIS light is or has been limited to less than 1.5 eV, preferably less than 0.75 eV.

[0035] For the irradiation of UV / VIS light in the first and / or second spectral ranges, it is possible to use non-tunable light sources, such as laser sources, e.g., excimer lasers, but also VUV LEDs. In this case, the light source(s) are selected so as to satisfy the above-mentioned conditions regarding average energy and bandwidth. Alternatively, one or more tunable light sources can be used for the irradiation of UV / VIS light. In this case, the average energy can be set and / or the bandwidth can be appropriately limited. Within the meaning of this application, the average energy of a spectral range is understood to be the central wavelength of the spectral range. Within the meaning of this application, the bandwidth of a spectral range is understood to be the full width at half maximum. In principle, it is also possible to use a single broadband light source for the irradiation of UV / VIS light and to generate the desired spectral range using appropriate wavelength filters.

[0036] In yet another variant of the method, the ratio of the intensity of UV / VIS light in the first spectral range to the intensity of UV / VIS light in the second spectral range is greater than 3:1, preferably greater than 6:1. The intensity of UV / VIS light in the first spectral range must be set so that the rate of annealing of crystal defects is greater than the rate of generation of new crystal defects. In the case of ion-assisted deposition, the generation rate consists of defect formation as a result of ion bombardment and defect formation as a result of single-photon processes induced by VUV. If UV / VIS light in the second spectral range near the band edge of an ionically bonded solid, such as a fluoride or oxide, is used for irradiation, it is advantageous to correspondingly increase the intensity of the first spectral range.

[0037] In yet another variant of the method, the ion-bonding solid is an oxide or a fluoride. An oxide suitable for the VUV wavelength range is, for example, SiO2. Suitable fluorides are, for example, magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, thiolite, cryolite, erbium fluoride, neodymium fluoride, gadolinium fluoride, dysprosium fluoride, samarium fluoride, holmium fluoride, hafnium fluoride, lanthanum fluoride, europium fluoride, lutetium fluoride, cerium fluoride, barium fluoride, or yttrium fluoride. These fluorides have low absorption and relatively high radiation resistance in the VUV wavelength range. For the deposition of multilayer coatings containing two or more different fluorides on a substrate, irradiation is generally performed during the deposition of each individual layer using a specific light source or specific first and / or second spectral ranges adapted to the materials being deposited.

[0038] In yet another variant of the method, the deposition is performed with plasma and / or ion assistance. As mentioned above, plasma and / or ion assistance methods can be used to deposit layers consisting of ionically bonded solids with high density. Corresponding methods are, for example, sputter deposition, arc evaporation, ion beam sputtering, and plasma-enhanced atomic layer deposition (ALD). However, plasmas generally also emit UV / VUV radiation. The short-wave portion of this radiation can generate crystalline defects through single-photon processes, which can adversely affect the optical performance and / or stability or irradiation stability of the layer. However, generally, the spectral range of the radiation emitted by the plasma can itself have a regenerative effect, which should be taken into account when fine-tuning the intensity of both of the above-mentioned spectral ranges.

[0039] Crystal defects that occur during plasma-assisted and / or ion-assisted coating can be instantly regenerated by UV / VIS light irradiation, so the combination of plasma-assisted and / or ion-assisted and UV / VIS light irradiation allows the deposition of layers with high density and at the same time low extinction coefficients.

[0040] In yet another variation of the method, the deposition is carried out in the presence of at least one reactive gas, typically inside a coating chamber supplied with the reactive gas via a gas inlet.

[0041] In one development of this variant, the at least one reactive gas is selected from the group comprising F2, O2, NF3, XeF2, SF6, CF4, NH3. Preferably, the reactive gas contains F2 and / or O2. The reactive gas serves to maintain the stoichiometry of the deposited layer, especially during plasma-assisted or ion-assisted processes.

[0042] In yet another variation of the method, the deposition is -6 mbar~10 -2 The deposition is generally carried out under vacuum conditions in the coating chamber. The (total) pressure during deposition is generally determined by the sputtering gas or by the (process) gas to be ionized. This gas is generally a noble gas, often Ar. If a reactive gas is used during deposition, it is metered in only in small amounts sufficient to counteract substoichiometry (preferential sputtering of light elements, e.g., O or F).

[0043] According to a further aspect, the above-mentioned object is also achieved by an apparatus of the type described above, comprising one or more UV / VIS light sources for irradiating the layer with UV / VIS light during deposition. With regard to the advantages achieved by the apparatus and its embodiments described below, reference is made to the above description of the method and its variants. The UV / VIS light source can be a light source designed to emit UV light (UV light source) or VIS light (VIS light source). It is also possible to design the light source to emit both UV and VIS light.

[0044] In one embodiment, at least one of the one or more UV / VIS light sources is spectrally tunable. Tunable UV / VIS light sources are particularly suitable for this application, since their spectrum can be easily adapted to different crystal defects and different materials. In particular, their spectrum can be set so that no defect transformation occurs and no new crystal defects are formed. Suitable tunable UV / VIS light sources are, for example, broadband light sources that allow downstream wavelength selection. In the case of UV light, for example, D2 gas discharge lamps with downstream wavelength selection can be involved. Plasma light sources can also be used for this purpose.

[0045] In yet another embodiment, at least one of the one or more UV / VIS light sources is designed to emit UV / VIS light in a first spectral range for annealing at least one crystalline defect in the ionically bonded solid, the first spectral range at least partially overlapping an absorption region of the at least one crystalline defect, the first spectral range preferably including the absorption energy of the crystalline defect. The (at least one) UV / VIS light source can be designed to vary the central wavelength and / or bandwidth of the emitted UV / VIS light, although UV / VIS light sources with predefined, fixed central wavelength and bandwidth can also be involved.

[0046] In yet another embodiment, the or at least one of the plurality of UV / VIS light sources is designed to emit UV / VIS light in a second spectral range for transferring atoms at the surface of the ionically bonded solid, said second spectral range being in an energy range of 75% to 100%, preferably 80% to 95%, of the band gap energy of the ionically bonded solid.

[0047] In the simplest case, a first UV / VIS light source is designed to emit light in a first spectral range and a second UV / VIS light source is designed to emit UV / VIS light in a second spectral range. Irradiation in the first and second spectral ranges is generally performed synchronously, i.e., both UV / VIS light sources emit UV / VIS light in their respective spectral ranges simultaneously.

[0048] In yet another embodiment, the apparatus comprises a plasma source and / or an ion source to enable plasma-assisted and / or ion-assisted deposition.

[0049] In yet another embodiment, the apparatus comprises a supply device for supplying at least one reactive gas to the coating chamber, the at least one reactive gas being selected from the group including, for example, F2, O2, NF3, XeF2, SF6, CF4, and NH3.

[0050] Yet another aspect of the present invention relates to an optical element for reflecting and / or transmitting radiation in the VUV wavelength range, comprising a substrate coated with at least one layer of an ionically bonded solid, the at least one layer being deposited according to the method and / or by the apparatus described above. The optical element may be a transmissive optical element, for example a laser chamber window of an excimer laser. In this case, the exterior of the laser chamber window is typically coated with a high-density fluoride layer. However, the optical element may also be a reflective optical element, for example a mirror serving to deflect or focus radiation in the VUV wavelength range, or a beam splitter serving to transmit and reflect radiation in the VUV wavelength range.

[0051] A further aspect of the invention relates to an optical device for the VUV wavelength range, in particular a VUV lithography device or a wafer inspection system, comprising at least one optical element as described above. The optical device may be, for example, a (VUV) lithography system, a wafer or mask inspection system, a laser system, etc.

[0052] Further features and advantages of the present invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawings which show the details essential to the invention, and from the claims. Each of the individual features can be implemented alone or in any combination of several in a variant of the invention.

[0053] Exemplary embodiments are shown in the schematic drawings and explained in the following description. [Brief explanation of the drawings]

[0054] [Figure 1] 1 shows a schematic diagram of an apparatus for depositing a layer on a substrate, equipped with two UV light sources emitting UV light in two spectral ranges. [Figure 2] The absorption spectrum of MgF2, including the absorption region of the F center, the two spectral regions of UV light from Figure 1, and the emission spectrum of Ar plasma are shown. [Figure 3] The dependence of the absorption energy of crystal defects on the anion-cation distance for various fluorides is shown. [Figure 4] Figure 4a, b shows the effect of UV / VIS light irradiation on fluoride crystal defects as a function of the absorption energy of the crystal defects and the energy of the UV / VIS light. [Figure 5] 1 shows a schematic diagram of an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus. [Figure 6] 1 shows a schematic diagram of an optical arrangement for the VUV wavelength range in the form of a wafer inspection system. [Figure 7] 1 shows a schematic diagram of an optical element in the form of a laser chamber window. DETAILED DESCRIPTION OF THE INVENTION

[0055] 1 shows an apparatus 1 for depositing one or more layers 2 on a substrate 3. For this purpose, the apparatus 1 comprises a coating chamber 4 in the form of a vacuum chamber, in which a mount 5 (manipulator) for the substrate 3 is mounted in the manner of a rotary table. An electric potential (bias) can be applied to the mount 5, for example in order to accelerate ions from the plasma in the direction of the substrate 3. A vacuum pump 6 serves to generate a vacuum inside the coating chamber 4.

[0056] The apparatus 1 has a coating source 7 designed to convert a coating material 8 into a gas phase and deposit it as a layer 2 on the substrate 3 in the coating chamber 4. In the example shown, the coating material 8 is an ionically bonded solid in the form of a fluoride, more precisely magnesium fluoride. However, the coating material 8 can also be any other ionically bonded solid, for example an oxide. To convert the coating material 8 into a gas phase, the coating source 7 can be designed in various ways, for example as a thermal evaporator, as a sputtering source or as an electron beam evaporator. It is also possible for the apparatus 1 to have more than one coating source 7 to deposit one or more layers 2 on the substrate 3.

[0057] The deposition of layer 2 onto substrate 3 (or onto a further layer already applied to substrate 3) can be carried out without plasma and / or ion assistance. However, to produce a layer 2 with a high density, it is advantageous if the deposition of layer 2 is carried out with ion and / or plasma assistance. In the example of plasma-assisted deposition shown in Figure 1, apparatus 1 comprises a plasma source 9 designed to generate an argon plasma. As an alternative or in addition to one or more plasma sources 9, apparatus 1 can also comprise one or more ion sources, which are not shown in Figure 1.

[0058] In order to maintain the stoichiometry of the deposited layer 2 during plasma-assisted or plasma-ion-assisted deposition, the deposition must be carried out in the presence of at least one reactive gas R. The apparatus 1 comprises a supply device 10 for supplying at least one reactive gas R to the coating chamber 4. The supply device 10 comprises a gas inlet of the coating chamber 4 as well as a valve device that allows for the controlled supply of the reactive gas R from a gas reservoir to the coating chamber 4. The supplied reactive gas R can be, for example, a gas containing F2 and / or O2, such as XeF2, NF3, SF6, or CF4, but can also be any other type of reactive gas, such as NH3.

[0059] The supply device 10 also comprises a further valve device which serves to supply in a controlled manner an inert gas I from a further gas reservoir to the coating chamber 4. The inert gas I may, for example, be a noble gas, such as argon, which may serve in particular to vent the coating chamber 4 before opening it or to set a pressure p inside the coating chamber 4.

[0060] The pressure p inside the coating chamber 4 is generally about 10 -6 mbar to approximately 10 -2 The pressure p is essentially determined by the partial pressure of the inert gas I and / or reactive gas R admitted to the coating chamber 4.

[0061] A high fluorine partial pressure is particularly advantageous when, during deposition, the layer 2 is irradiated with UV light 11a, 11b generated by first and second UV light sources 12a, 12b of the apparatus 1 shown in Figure 1. In the example shown in Figure 1, the first UV light source 12a is designed to emit UV light 11a in a first spectral range 13a, which serves to anneal crystalline defects during deposition. The second UV light source 12b is designed to emit UV light 11b in a second spectral range 13b, which serves to move atoms at the surface 2a of the ionically bonded solid or layer 2. The two spectral ranges 13a, 13b are shown in Figure 2 and will be described in more detail below in connection with Figure 2.

[0062] 1, the device 1 can have a single UV light source that emits UV light 11 a, 11 b in both the first spectral range 13 a and the second spectral range 13 b. The device can also have only a first UV light source 12 a that emits UV light 11 a in the first spectral range 13 a, or only a second UV light source 12 b that emits UV light 11 b in the second spectral range 13 b. The device 1 can also have more than one UV light source.

[0063] In the illustrated example, both the first UV light source 12a and the second UV light source 12b are designed to emit UV light 11a, 11b in fixedly defined first and second spectral ranges 13a, 13b, respectively. However, it is also possible for the first and / or second UV light sources 12a, 12b to be tunable so that the first and / or second spectral ranges 13a, 13b can be set or adjusted. In the example shown in Figure 2, the first UV light source 12a is a Nd:YAG laser with a wavelength of 266 nm, and the second UV light source 12b is a D2 lamp.

[0064] Alternatively, one or both light sources 12a, 12b can be designed to generate light in the visible wavelength range (VIS light). In this case, light sources 12a, 12b can be designed to emit VIS light in predetermined first and second spectral ranges 13a, 13b, respectively, or light sources 12a, 12b can be designed to be tunable. Furthermore, a single VIS light source can be designed to generate VIS light in both the first spectral range 13a and the second spectral range 13b. One or more UV light sources and one or more VIS light sources can also be provided.

[0065] As can also be seen in FIG. 1 , the two UV light sources 12a, 12b are protected from the interior of the coating chamber 4 by transmitting optical elements 14a, 14b. In the illustrated example, the transmitting optical elements 14a, 14b are lens elements, for example made of MgF2 or CaF2, that serve to focus or align the UV light 11a, 11b onto the deposited layer 2 or substrate 3. As can be seen in FIG. 1 , the optical axes of the two UV light sources 12a, 12b intersect at a common position Z at the center of the substrate 3. The coating source 7 and the plasma source 9 are also aligned with this common position Z. Instead of the transmitting optical elements 14a, 14b in the form of lens elements, it is also possible to use windows, i.e., plane-parallel plates, to protect the UV light sources 12a, 12b from the interior of the coating chamber 4. In general, the entire substrate 3 should be illuminated as uniformly as possible with the UV light 11a, 11b.

[0066] FIG. 2 shows the absorption spectrum of an ionic solid in the form of MgF2 as a function of energy and wavelength. The vertical axis shows the absorption coefficient in arbitrary units and logarithmic representation. The absorption spectrum of a single crystal of MgF2 and that of a thin MgF2 layer are shown on the right side of FIG. 2. These absorption spectra are discussed in detail in the article "Vacuum ultraviolet loss in magnesium fluoride films," OR Wood II et al., Appl. Opt. 23, 3644 (1984), which is incorporated herein by reference in its entirety.

[0067] Also evident from Figure 2 are absorption regions 16 of crystal defects in the form of color centers, more precisely F-centers, in the deposited MgF2 material. The color centers 15 are located at the absorption energy E abs In the illustrated example, this absorbed energy E abs The wavelength corresponding to the absorption energy E of the F center 15 is about 260 nm or about 4.77 eV. abs Also shown is the absorption region 16 of the F-center 15, defined by the drop in the absorption coefficient to half maximum (FWHM) at 1000 kJ / cm. In the example shown in Figure 2, the absorption region 16 of the F-center 15 is from about 4.3 eV to about 5.25 eV.

[0068] As can be seen in FIG. 2, the first spectral region 13a has an average energy E of about 4.66 eV, which corresponds to a wavelength of about 266 nm. M1 This average energy E M1 corresponds to the center wavelength of the first UV light source 12a, which is at the center of the bandwidth 17 of the first spectral range 13a. In the illustrated example, the bandwidth 17 of the first spectral range 13a is about 0.5 eV.

[0069] The first spectral range 13a, which serves to anneal the F-center 15, therefore overlaps the absorption region 16 of the F-center 15. More precisely, the first spectral range 13a is entirely within the absorption region 16 of the F-center 15. The first spectral range 13a therefore overlaps the absorption energy E abs Also includes.

[0070] The mean energy E of the first spectral region 13a M1 is the absorbed energy E abs 1.5 eV, preferably less than 0.75 eV. This is the case in the present application, since the bandwidth (FWHM) of the first spectral range 13a is less than approximately 0.5 eV.

[0071] The first spectral region 13a, in particular the mean energy E M1 and the selection of its bandwidth 17 is based on the absorption energy E of each crystal defect 15 of the deposited material in the form of an ionically bonded solid. abs Any other photoaddressable or annealable color center or any other crystalline defect may also be involved here instead of the F-center 15.

[0072] Figure 3 shows the absorption energy E of crystal defects versus the anion-cation distance a of various fluorides. abs The following dependencies are shown:

[0073] The F-centers of fluorides with cubic crystal structure are determined by the Mollwo-Ivey rule, i.e., the relationship E abs =Ca -n (1) where C≈0.26 (unit: nm) and n≈1.8. As can be seen in Figure 3, for example, in the case of MgF2, this law is followed by the absorption energy E of about 4.77 eV shown above. abs is obtained.

[0074] For more complex crystal structures and / or other color centers, deviations from this law occur, but it can still be used relatively approximately. A more accurate description is obtained if the constant C and the exponent n in the power law (1) are adapted to the case under consideration, for example by fitting.

[0075] Due to this relationship, the absorption energy E of the crystal defect 15 is roughly determined by the anion-cation distance a. abs Therefore, the first spectral range 13a of the UV / VIS light 11a required for the regeneration or bleaching of the crystal defects 15 is appropriately selected based on the average energy E M1 can be estimated from the crystal structure of the deposited material. This is advantageous because the absorbed energy E abs The mean energy E of the first spectral region 13a from M1 If the deviation is too large, in the worst case scenario, it may lead to the formation of new crystal defects 15 rather than annealing the crystal defects 15, as will be explained below with reference to FIGS. 4a and 4b.

[0076] FIG. 4a shows a scatter plot of the effect of UV / VIS light 11a irradiation on fluoride crystal defects 15a to 15c. The horizontal axis represents the (average) energy E of the UV / VIS light. M1 The vertical axis corresponds to the absorbed energy E of the crystal defect. abs In this case, three different symbols represent crystal defects 15a that anneal and heal as a result of irradiation, crystal defects 15b that do not anneal and heal as a result of irradiation, and crystal defects 15c that are further created by irradiation. A total of 73 data points shown were obtained from a literature search.

[0077] FIG. 4b shows a histogram corresponding to FIG. 4a. In this case, the horizontal axis represents the absorbed energy E of the crystal defect 15. abs and the average energy E of the incident UV / VIS light 11a M1 The difference between abs -E M1The vertical axis corresponds to the number of corresponding crystal defects 15a to 15c. Three frequency distributions that can be approximated by a normal distribution are obtained for the annealable crystal defects 15a, the non-annealable crystal defects 15b, and the further generated crystal defects 15c. The mean values ​​of the normal distributions are 0.2 eV (annealable crystal defects 15a), 1.4 eV (non-annealable crystal defects 15b), and -1.1 eV (further generated crystal defects 15c). The full widths at half maximum are 1.6 eV (annealable crystal defects 15a), 1.4 eV (non-annealable crystal defects 15b), and 3.3 eV (further generated crystal defects 15c).

[0078] From Figures 4a and 4b, the average energy E of the UV / VIS light 11a M1 is the absorption energy E of the crystal defect 15 abs It is clear that the generation of further crystal defects 15c increases when the energy spectrum of the first spectral range 13a of the UV / VIS light 11a, in particular the average energy E M1 It is advantageous to impose an upper bound on the average energy E M1 is the absorption energy E of the crystal defect 15 to be annealed. abs 4a and 4b, the (average) energy E of the UV / VIS light 11a used during irradiation should be greater than a value in the range of 1 eV or less, preferably 1.5 eV or less. M1 is the absorbed energy E of each crystal defect 15 abs It is further evident that annealing is not possible when the temperature is significantly less than .

[0079] As mentioned above, Figure 2 shows the band gap energy E GThe absorption coefficient in the conduction band region or band edge of MgF2 with . . . is shown on the right. In this case, the solid line represents the absorption coefficient profile of the monocrystalline MgF2 material, and the dashed line represents the absorption coefficient of a thin layer 2 of MgF2 material as deposited using the apparatus 1 shown in Figure 1. For a thin layer of MgF2, the absorption coefficient decreases exponentially towards lower energies with a so-called Urbach tail 18. The band gap energy E of about 12.3 eV G Below this, the exciton state with the maximum absorption coefficient, for example the 1s exciton state, is excited.

[0080] As can be seen in Figure 2, during deposition UV light 11b in a second spectral range 13b is irradiated onto layer 2 or onto the deposited material of layer 2. The second spectral range 13b is typically within the band gap energy E of MgF2. G In the illustrated example, the second spectral region 13b is in the energy range of 9.84 eV to 11.8 eV, i.e., 75% to 100% of the band gap energy E of the deposited MgF2 material. G Therefore, the bandwidth 19 of the second spectral region 13b is about 1.96 eV, and the average energy E M2 The band edge energy E is approximately 10.82 eV. G The incidence of UV light 11b in a second spectral range 13b at or slightly below this acts to move atoms at the surface 2a of the layer 2 of MgF2 material.

[0081] Irradiation with UV light 11b in the second spectral range 13b during deposition typically reduces the extinction coefficient of the deposited layer 2. A possible mechanism here is that the Ehrlich-Schwobel barrier can be overcome more easily by the migrating atoms, allowing larger grains and fewer grain boundaries to be obtained during deposition, resulting in a lower extinction coefficient.

[0082] The intensity I1 of the UV light 11a in the first spectral range 13a must be set so that the rate of annealing of the crystal defects 15 is greater than the rate of generation of new crystal defects 15. The rate of generation of defects is also correlated with the VUV-induced single-photon processes. The band edge energy E of the ionic solid is G If UV light 11b in the adjacent second spectral range 13b is used for irradiation, it is advantageous to increase the intensity I1 emitted by the first UV light source 12a in the first spectral range 13a relative to the intensity I2 emitted by the UV light source 12b in the second spectral range 13b. Advantageously, the ratio of the intensity I1 of the UV light 11a in the first spectral range 12a to the intensity I2 of the UV light 11b in the second spectral range 13b is greater than 3:1, in particular greater than 6:1.

[0083] As explained above, ion-assisted and / or plasma-assisted processes can be used to deposit the high-density layer 2. In the case of ion-assisted deposition, crystalline defects 15 are also generated by ion bombardment. These crystalline defects 15 are intended to be substantially annealed by UV light 11a irradiated onto the layer 2 in the first spectral range 13a. In the case of plasma-assisted processes, it should be taken into account that the plasma also emits radiation in the UV / VUV wavelength range. Figure 2 shows, as an example, an emission spectrum 20 of a plasma for an argon-based RF-excited "cylindrical dielectric barrier discharge" process from the paper "VUV emission from a cylindrical dielectric barrier discharge in Ar and in Ar / N2 and Ar / air mixtures," N. Masoud et al., J. Phys. D 38, 1674-1683 (2005). The radiation of such a plasma generated by the plasma source 9 shown in Figure 1 also generates crystalline defects 15 in the deposited layer 2 by a single-photon process. In this respect, the emission spectrum 20 shown in Figure 2 overlaps with the Urbach tail 18 of the thin MgF2 layer 2. However, part of the radiation emitted by the plasma can also have a regenerative effect.

[0084] One or more layers 2 with low extinction coefficients and possibly high densities can be deposited on the substrate 3 as described above. The deposited layers 2 can perform various functions, such as protecting the substrate 3 or underlying layers, reflecting, or anti-reflection. The substrate 3 coated with one or more layers 2 can form optical elements designed to transmit and / or absorb radiation in the VUV wavelength range. Such transmitting and / or reflecting optical elements can be used in various optical devices for the VUV wavelength range. Reflecting optical elements can be, for example, mirrors, and transmitting / reflecting optical elements can be, for example, beam splitters.

[0085] Figure 5 shows an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus 21. The VUV lithography apparatus 21 comprises two optical systems: an illumination system 22 and a projection system 23. The VUV lithography apparatus 21 further comprises a radiation source 24, which may for example be an excimer laser.

[0086] Radiation 25 emitted by radiation source 24 is conditioned using illumination system 22 so that mask 26, also called a reticle, is illuminated. In the illustrated example, illumination system 22 has a housing 32 in which both transmissive and reflective optical elements are disposed. Typically, the figure shows transmissive optical element 27, which focuses radiation 25, and reflective optical element 28, which deflects the radiation.

[0087] The mask 26 has on its surface a structure that is to be transferred onto an optical element 29, e.g., a wafer, that is exposed by means of the projection system 23 in order to manufacture semiconductor components. In the example shown, the mask 26 is designed as a transmissive optical element. In an alternative embodiment, the mask 26 can also be designed as a reflective optical element.

[0088] The projection system 22 in the illustrated example comprises at least one transmissive optical element. The illustrated example typically shows two transmissive optical elements 30, 31 which serve, for example, to reduce structures on the mask 26 to a size desired for exposure of the wafer 29.

[0089] A wide variety of transmissive, reflective, or other optical elements can be combined with each other in any number of complex ways in both illumination system 22 and projection system 23. Optical arrangements without transmissive optical elements can also be used in VUV lithography.

[0090] FIG. 6 shows an optical arrangement for the VUV wavelength range in the form of a wafer inspection system 41, although a mask inspection system may also be involved. The wafer inspection system 41 comprises an optical system 42 with a radiation source 54, which directs radiation 55 from the radiation source 54 towards a wafer 49. For this purpose, the radiation 55 is reflected towards the wafer 49 by a concave mirror 46. In the case of a mask inspection system, a mask to be inspected may be arranged instead of the wafer 49. The radiation reflected, diffracted, and / or refracted by the wafer 49 is directed via a transmissive optical element 47 by a further concave mirror 48, also associated with the optical system 42, towards a detector 50 for further evaluation. The wafer inspection system 41 further comprises a housing 52 in which the two mirrors 46, 48 and the transmissive optical element 47 are arranged. The radiation source 54 may be, for example, exactly one radiation source or a combination of several individual radiation sources to provide a substantially continuous radiation spectrum. In a variant, one or more narrowband radiation sources 54 may also be used.

[0091] At least one of the optical elements 27, 28, 30, 31 of the VUV lithography apparatus 21 shown in Figure 5 and at least one of the optical elements 46, 47, 48 of the wafer inspection system 41 shown in Figure 6 are now designed as described above and are therefore coated with at least one layer 2 of an ion-bonding solid, for example a fluoride or an oxide, the at least one layer 2 having been deposited according to the method and / or by means of the apparatus 1 described above.

[0092] FIG. 7 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 passes to the exterior through the laser chamber window 60. The exterior of the laser chamber window 60 is coated with a layer 2 of an ionically bonded solid, e.g., a fluoride layer, deposited according to the method and / or by the apparatus 1 described above. The layer 2 is irradiated with UV / VUV light 11 a, 11 b during deposition and therefore has both a high density and a low extinction coefficient. Sealing with such layer 2 inhibits degradation of the laser chamber window 60 and therefore extends its lifetime.

Claims

1. A method for depositing at least one layer (2) of an ionically bonded solid on a substrate (3), said ionically bonded solid being a fluoride or an oxide, converting the coating material (8) into a gas phase; depositing the coating material (8) converted into a gas phase onto the substrate (3); In a method comprising: During deposition, the layer (2) is irradiated with UV / VIS light (11a, 11b), the UV / VIS light (11a) having a first spectral range (13a) at least partially overlapping an absorption region (16) of at least one crystalline defect (15) of the ionically bonded solid for annealing the at least one crystalline defect (15), the first spectral range (13a) being greater than or equal to the absorption energy (E) of the crystalline defect (15). ａｂｓ ) and the mean energy (E Ｍ１ ) is the absorption energy (E ａｂｓ ) by 0.5 eV or less.

2. 2. The method of claim 1, wherein the mean energy (E Ｍ１ ) is the absorption energy (E ａｂｓ ) by 0.25 eV or less.

3. 3. The method according to claim 1 or 2, characterized in that the crystal defects form color centers, in particular F centers.

4. The method according to any one of claims 1 to 3, wherein the first spectral range (13a) is the absorption energy (E ａｂｓ and the anion-cation distance (a) of the ion-binding solid.

5. The method according to any one of claims 1 to 4, wherein the first spectral range (13a) is the absorption energy (E ａｂｓ ) is 1 eV or less, preferably 1.5 eV or less. Ｍ１ ) a method comprising:

6. The method according to any one of claims 1 to 5, wherein the UV / VIS light (11b) has a second spectral range (13b) for transferring atoms at the surface (2a) of the ionically bonded solid, the second spectral range (13b) being within the band gap energy (E) of the ionically bonded solid. Ｇ ) in an energy range of 75% to 100%, preferably 80% to 95%.

7. 7. The method according to claim 6, wherein the average energy (E) of the first spectral range (13a) and / or the second spectral range (13b) of the UV / VIS light (11a, 11b) is Ｍ１ , E Ｍ２ ) is or has been set to less than 0.5 eV, preferably less than 0.25 eV, and / or the bandwidth (17, 19) of the first spectral range (13a) and / or the second spectral range (13b) of the UV / VIS light (11a, 11b) is or has been limited to less than 1.5 eV, preferably less than 0.75 eV.

8. 7. The method according to claim 6, wherein the intensity (I) of the UV / VIS light (11a) in the first spectral range (12a) is １ ) and the intensity (I) of the UV / VIS light (11b) in the second spectral range (13b). ２ ) is greater than 3:1, preferably greater than 6:

1.

9. A method according to any one of the preceding claims, characterized in that the deposition is plasma-assisted and / or ion-assisted.

10. A method according to any one of the preceding claims, characterized in that the deposition is carried out in the presence of at least one reactive gas (R).

11. 11. The method of claim 10, wherein the at least one reactive gas (R) is F ２ , O ２ , N.F. ３ , XeF ２ , S.F. ６ , C.F. ４ , N.H. ３ The method according to claim 1, wherein the compound is selected from the group consisting of:

12. 12. The method of claim 10 or 11, wherein the deposition is －６ mbar~10 －２ 3. A process characterized in that it is carried out at a pressure (p) in the range of 1000 to 1000 mbar.

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