METHOD AND APPARATUS FOR DEPOSITION OF AT LEAST ONE LAYER, OPTICAL ELEMENT AND OPTICAL ARRANGEMENT

Abstract

The disclosed techniques relate to a method for depositing at least one layer composed of an ionically bonded solid on a substrate, comprising the following steps: converting a coating material to the gas phase and depositing the coating material converted to the gas phase on the substrate. The layer is irradiated with UV/VIS light during the deposition. The disclosed techniques also relate to an apparatus for implementing the disclosed method and optical elements and devices created using the disclosed method.

Claims

1. A method for depositing at least one layer composed of an ionically bonded solid on a substrate, comprising: converting a coating material to a gas phase; depositing the coating material converted to the gas phase on the substrate forming the ionically bonded solid on the substrate; and irradiating the coating material converted to the gas phase with UV/VIS light during the depositing, wherein the UV/VIS light comprises a first spectral range for annealing at least one crystal defect of the ionically bonded solid, wherein the first spectral range at least partly overlaps an absorption range of the at least one crystal defect, wherein the first spectral range comprises an absorption energy of the at least one crystal defect, and wherein a mean energy of the first spectral range deviates from the absorption energy of the at least one crystal defect by 0.5 eV or less.

2. The method as claimed in claim 1, wherein the mean energy of the first spectral range deviates from the absorption energy of the at least one crystal defect by 0.25 eV or less.

3. The method of claim 1, wherein the at least one crystal defect forms a color center.

4. The method of claim 1, wherein the first spectral range is chosen based on a relationship between the absorption energy of the at least one crystal defect and an anion-cation distance of the ionically bonded solid.

5. The method of claim 1, wherein the mean energy of the first spectral range is greater than the absorption energy of the at least one crystal defect by 1 eV or less.

6. The method of claim 1, wherein the UV/VIS light comprises a second spectral range for mobilizing atoms at a surface of the ionically bonded solid, the second spectral range lying in an energy range of between 75% and 100% of a bandgap energy of the ionically bonded solid.

7. The method of claim 6, wherein the mean energy of the first spectral range or a mean energy of the second spectral range is less than 0.5 eV or a bandwidth of the first spectral range or a bandwidth of the second spectral range is restricted to less than 1.5 eV.

8. The method of claim 6, wherein a ratio between an intensity of the UV/VIS light in the first spectral range and an intensity of the UV/VIS light in the second spectral range is more than 3:1.

9. The method of claim 1, wherein the ionically bonded solid is a fluoride or an oxide.

10. The method of claim 1, wherein the depositing comprises a plasma-assisted and/or ion-assisted deposition.

11. The method of claim 1, wherein the depositing is carried out in the presence of at least one reactive gas.

12. The method of claim 11, wherein the at least one reactive gas is selected from the group comprising: F.sub.2, O.sub.2, NF.sub.3, XeF.sub.2, SF.sub.6, CF.sub.4, and NH.sub.3.

13. The method of claim 12, wherein the depositing is carried out at a pressure in a range of between 10.sup.6 mbar and 10.sup.2 mbar.

14. An apparatus for depositing at least one layer composed of an ionically bonded solid, comprising: a coating chamber having a mount for a substrate; a coating source designed to convert a coating material to a gas phase and to deposit it as a layer on the substrate within the coating chamber; and one or more UV/VIS light sources configured to irradiate the layer with UV/VIS light during deposition of the coating material by the coating source, wherein the one or more UV/VIS light sources are designed to emit UV/VIS light in a first spectral range for mobilizing atoms at a surface of the ionically bonded solid, which lies in an energy range of between 75% and 100% of a bandgap energy (E.sub.G) of the ionically bonded solid.

15. The apparatus of claim 14, wherein the one or more UV/VIS light sources are spectrally tunable.

16. The apparatus of claim 14, wherein at least one of the one or more UV/VIS light sources is designed to emit UV/VIS light in a second spectral range for annealing at least one crystal defect of the ionically bonded solid, wherein the second spectral range at least partly overlaps an absorption range of the at least one crystal defect, the first spectral range preferably comprising an absorption energy of the at least one crystal defect.

17. The apparatus of claim 14, further comprising a plasma source and/or an ion source.

18. The apparatus of claim 14, further comprising a feed feeding at least one reactive gas into the coating chamber.

19. An optical element for reflecting and/or transmitting radiation in a VUV wavelength range, comprising: a substrate coated with at least one layer composed of an ionically bonded solid, characterized in that the at least one layer was deposited according to a method as claimed in claim 1.

20. 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 claimed in claim 19.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Examples of the disclosed techniques are illustrated in the schematic drawing and are explained in the following description. In the figures:

[0052] FIG. 1 shows a schematic illustration of an apparatus for depositing layers on a substrate, the apparatus comprising two UV light sources for emitting UV light in two spectral ranges,

[0053] FIG. 2 shows the absorption spectrum of MgF.sub.2 including an absorption range of an F-center, the two spectral ranges of the UV light from FIG. 1 and the emission spectrum of an Ar plasma,

[0054] FIG. 3 shows the dependence of the absorption energy of crystal defects on the anion-cation distance for various fluorides,

[0055] FIGS. 4A and 4B show the effect of the irradiation with UV/VIS light on crystal defects in fluorides as a function of the absorption energy of the crystal defects and the energy of the UV/VIS light,

[0056] FIG. 5 shows a schematic illustration of an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus,

[0057] FIG. 6 shows a schematic illustration of an optical arrangement for the VUV wavelength range in the form of a wafer inspection system, and

[0058] FIG. 7 shows a schematic illustration of an optical element in the form of a laser chamber window.

DETAILED DESCRIPTION

[0059] FIG. 1 shows an apparatus 1 for depositing one or a plurality of layers 2 on a substrate 3. For this purpose, the apparatus 1 includes a coating chamber 4 in the form of a vacuum chamber, in which a mount 5 (manipulator), in the form of a rotary table, is provided for the substrate 3. An electrical potential (bias) may be applied to the mount 5, for example in order to accelerate ions from a plasma in the direction of the substrate 3. A vacuum pump 6 generates a vacuum in an interior of the coating chamber 4.

[0060] The apparatus 1 has a coating source 7 designed to convert a coating material 8 to the gas phase and to deposit it as a layer 2 on the substrate 3 within 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 may also be some other ionically bonded solid, e.g., an oxide. In order to convert the coating material 8 to the gas phase, the coating source 7 may 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 two or more coating sources 7 in order to deposit one or a plurality of layers 2 on the substrate 3.

[0061] The deposition of the layer 2 on the substrate 3 (or on a further layer already applied on the substrate 3) may be performed without plasma and/or ion assistance. In order to produce a layer 2 having a high density, however, it is advantageous if the deposition of the layer 2 is performed in an ion-assisted and/or plasma-assisted manner. In the example shown in FIG. 1 for plasma-assisted deposition, the apparatus 1 has a plasma source 9 designed for generating an argon plasma. As an alternative or in addition to one or a plurality of plasma source(s) 9, the apparatus 1 may also have one or a plurality of ion source(s), the illustration of which has been dispensed with in FIG. 1.

[0062] In order to maintain the stoichiometry of the deposited layer 2 during the plasma-assisted or plasma ion-assisted deposition, the deposition may be performed in the presence of at least one reactive gas R. The apparatus 1 has a feed 10 feeding the at least one reactive gas R into the coating chamber 4. The feed 10 includes a valve arrangement besides a gas inlet in the coating chamber 4, said valve arrangement enabling a controlled feed of the reactive gas R from a gas reservoir into the coating chamber 4. The reactive gas R fed in may be for example a gas containing F.sub.2 and/or O.sub.2, e.g., XeF.sub.2, NF.sub.3, SF.sub.6 or CF.sub.4, but also some other type of reactive gas, for example NH.sub.3.

[0063] The feed 10 also has a further valve arrangement serving for the controlled feed of an inert gas I from a further gas reservoir into the coating chamber 4. The inert gas I may be, for example, a noble gas, e.g., argon, which may serve inter alia for ventilating the coating chamber 4 prior to opening or for setting the pressure p in the interior of the coating chamber 4.

[0064] The pressure p in the interior of the coating chamber 4 is generally between approximately 10.sup.6 mbar and approximately 10.sup.2 mbar during the deposition. The pressure p is substantially determined by the partial pressure of the inert gas I and/or reactive gas R admitted into the coating chamber 4.

[0065] An increased fluorine partial pressure may be advantageous if during the deposition, the layer 2 is irradiated with UV light 11a, 11b generated by a first and second UV light source 12a, 12b of the apparatus 1 shown in FIG. 1. In the example shown in FIG. 1, the first UV light source 12a is designed to emit UV light 11a in a first spectral range 13a, which serves for annealing crystal defects during the deposition. The second UV light source 12b is designed to emit UV light 11b in a second spectral range 13b, which serves for mobilizing atoms at the surface 2a of the ionically bonded solid or the layer 2. The two spectral ranges 13a, 13b are illustrated in FIG. 2 and are described in greater detail further below in association with FIG. 2.

[0066] In a departure from the illustration in FIG. 1, the apparatus 1 may have a single UV light source, which emits UV light 11a, 11b both in the first spectral range 13a and in the second spectral range 13b. The apparatus may also have only the first UV light source 12a, which emits UV light 11a in the first spectral range 13a, or only the second UV light source 12b, which emits UV light 11b in the second spectral range 13b. The apparatus 1 may also have more than two UV light sources.

[0067] In the example shown, both the first UV light source 12a and the second UV light source 12b are designed for emitting UV light 11a, 11b in fixed, predefined first and second spectral range 13a, 13b, respectively. However, it is also possible for the first and/or the second UV light source 12a, 12b to be tunable in order to be able to set or tune the first and/or the second spectral range 13a, 13b. In the example shown in FIG. 2, the first UV light source 12a is an Nd:YAG laser having a wavelength of 266 nm, and the second UV light source 12b is a D.sub.2 lamp.

[0068] Alternatively, one or both light sources 12a, 12b may be designed for generating light in the visible wavelength range (VIS light). In this case, the light sources 12a, 12b may be designed for emitting VIS light in a predefined first and second spectral range 13a, 13b, respectively, or the light sources 12a, 12b may be designed to be tunable. Moreover, a single VIS light source may be designed to generate VIS light both in the first spectral range 13a and in the second spectral range 13b. One or a plurality of UV light sources and one or a plurality of VIS light sources may also be provided.

[0069] As is likewise discernible in FIG. 1, the two UV light sources 12a, 12b are protected from the interior of the coating chamber 4 by transmissive optical elements 14a, 14b. In the example shown, the transmissive optical elements 14a, 14b are lens elements, e.g., lenses composed of MgF.sub.2 or CaF.sub.2, which serve to focus or align the UV light 11a, 11b on the deposited layer 2 or on the substrate 3. As is discernible in FIG. 1, the optical axes of the two UV light sources 12a, 12b intersect at a common position Z in the center of the substrate 3. The coating source 7 and the plasma source 9 are likewise aligned with this common position Z. Instead of the transmissive optical elements 14a, 14b in the form of the lens elements, it is also possible to use windows, i.e., plane-parallel plates, in order to protect the UV light sources 12a, 12b from the interior of the coating chamber 4. Generally, the entire substrate 3 should be illuminated with the UV light 11a, 11b as homogeneously as possible.

[0070] FIG. 2 shows an absorption spectrum of an ionically bonded solid in the form of MgF.sub.2 as a function of energy and wavelength. The absorption coefficient is plotted in arbitrary units in a logarithmic representation on the ordinate axis. Both the absorption spectrum of an MgF.sub.2 single-crystal and the absorption spectrum of a thin MgF.sub.2 layer are illustrated on the right-hand side in FIG. 2. These absorption spectra are discussed in detail in the article Vacuum ultraviolet loss in magnesium fluoride films, O. R. Wood II et al., Appl. Opt. 23, 3644 (1984), which is hereby incorporated by reference in its entirety.

[0071] FIG. 2 likewise reveals an absorption range 16 of a crystal defect in the form of a color center 15, more precisely an F-center, of the deposited MgF.sub.2 material. The color center 15 has an absorption energy E.sub.abs at which the absorption coefficient of the F-center is at a maximum. In the example shown, the wavelength corresponding to the absorption energy E.sub.abs is at approximately 260 nm or at approximately 4.77 eV. FIG. 2 likewise illustrates an absorption range 16 of the F-center 15, which is defined by a decrease to half the maximum value of the absorption coefficient (FWHM) at the absorption energy E.sub.abs of the F-center 15. In the example shown in FIG. 2, the absorption range 16 of the color center 15 lies between approximately 4.3 eV and approximately 5.25 eV.

[0072] As is discernible in FIG. 2, the first spectral range 13a has a mean energy E.sub.M1 of approximately 4.66 eV, corresponding to a wavelength of approximately 266 nm. This mean energy E.sub.M1 corresponds to the central wavelength of the first UV light source 12a, which lies in the center of the bandwidth 17 of the first spectral range 13a. In the example shown, the bandwidth 17 of the first spectral range 13a is approximately 0.5 eV.

[0073] The first spectral range 13a, serving for annealing the F-center 15, thus overlaps the absorption range 16 of the F-center 15; to put it more precisely, the first spectral range 13a lies completely within the absorption range 16 of the F-center 15. The first spectral range 13a therefore also comprises the absorption energy E.sub.abs of the F-center 15.

[0074] The mean energy E.sub.M1 of the first spectral range 13a deviates from the absorption energy E.sub.abs only by 0.11 eV. This is advantageous in order to be able to instantaneously anneal the F-center 15 during the deposition of the layer 2. The bandwidth 16 of the first spectral range 13a should also be as narrow as possible for the annealing of the F-center 15 and should be set or settable to less than 1.5 eV, preferably to less than 0.75 eV. This is the case in the present example since the bandwidth (FWHM) of the first spectral range 13a is less than approximately 0.5 eV.

[0075] The selection of the first spectral range 13a, in particular the mean energy E.sub.M1 of the first spectral range 13a, and optionally the bandwidth 17 thereof, is dependent on the absorption energy E.sub.abs of a respective crystal defect 15 of the deposited material in the form of the ionically bonded solid. Some other color center or some other crystal defect which is optically addressable or annealable may also be involved here instead of an F-center 15.

[0076] FIG. 3 shows the dependence of the absorption energy E.sub.abs of crystal defects on the anion-cation distance a for various fluorides.

[0077] Illustrated in FIG. 3 are the F-centers 15 of fluorides having a cubic crystal structure that follow the Mollwo-Ivey rule to a very good approximation, i.e., the relationship:

E.sub.abs=Ca.sup.n(1)

where C0.26 (with a in units of nm) and n1.8. As is discernible in FIG. 3, for example the absorption energy E.sub.abs of approximately 4.77 eV indicated further above results for MgF.sub.2 in accordance with this rule.

[0078] For more complex crystal structures and/or other color centers, deviations from this rule arise, although the rule may continue to be used to a relatively good approximation. A more accurate description is obtained if the constant C and the exponent n in the power law (1) are adapted by way of, for example, a fit to the case under consideration.

[0079] On the basis of the absorption energy E.sub.abs of the crystal defect 15 that is determined approximately from the anion-cation distance a via the relationship, a suitable choice of the first spectral range 13a of the UV/VIS light 11a may be determined. The mean energy E.sub.M1 of the UV/VIS light 11a required for regenerating or bleaching the crystal defects 15 may thus be estimated from the crystal structure of the materials to be deposited. This is advantageous since an excessively large deviation of the mean energy E.sub.M1 of the first spectral range 13a from the absorption energy E.sub.abs, in the worst case, cannot lead to the annealing of the crystal defects 15, but rather to the formation of new crystal defects 15, as will be described below with reference to FIGS. 4A and 4B.

[0080] FIG. 4A illustrates the effect of the irradiation with UV/VIS light 11a on crystal defects 15a-c in fluorides in a scatter diagram. The abscissa corresponds to the (mean) energy E.sub.M1 of the UV/VIS light, and the ordinate corresponds to the absorption energy E.sub.abs of the crystal defect. In this case, the three different symbols stand for crystal defects which anneal as a result of the irradiation, crystal defects 15b which do not anneal as a result of the irradiation, and crystal defects 15c which are additionally produced by the irradiation. The total of seventy-three data points illustrated originate from a literature search.

[0081] FIG. 4B shows a histogram corresponding to FIG. 4A. In this case, the abscissa corresponds to the difference =E.sub.absE.sub.M1 between the absorption energy E.sub.abs of the crystal defect 15 and the mean energy E.sub.M1 of the incident UV/VIS light 11a. The ordinate corresponds to the number of corresponding crystal defects 15a-c. For the annealable crystal defects 15a, the non-annealable crystal defects 15b and the additionally produced crystal defects 15c, three frequency distributions arise, which may be approximated by normal distributions. The mean values of the normal distributions are 20 eV (annealable crystal defects 15a), 1.4 eV (non-annealable crystal defects 15b) and 1.1 eV (additionally produced crystal defects 15c). The full width at half maximum values are 1.6 eV (annealable crystal defects 15a), 1.4 eV (non-annealable crystal defects 15b) and 3.3 eV (additionally produced crystal defects 15c).

[0082] FIG. 4A and FIG. 4B reveal that increased production of additional crystal defects 15c occurs if the mean energy E.sub.M1 of the UV/VIS light 11a is significantly greater, typically at least 1 eV or 1.5 eV greater, than the absorption energy E.sub.abs of the crystal defect 15. It is therefore advantageous to impose an upward limitation on the spectrum of the energy of the first spectral range 13a of the UV/VIS light 11a and in particular the mean energy E.sub.M1. Specifically, the mean energy E.sub.M1 should not be more than 1 eV greater, preferably not more than 1.5 eV greater, than the absorption energy E.sub.abs of the crystal defect 15 that is to be annealed. FIG. 4A and FIG. 4B additionally reveal that no annealing is possible if the (mean) energy E.sub.M1 of the UV/VIS light 11a used during the irradiation is significantly less than the absorption energy E.sub.abs of the respective crystal defect 15.

[0083] As also described above, FIG. 2 illustrates on the right-hand side the absorption coefficient in the range of the conduction band of MgF.sub.2 with a bandgap energy EG or a band edge of the conduction band. In this case, a solid line represents the profile of the absorption coefficient in a monocrystalline MgF.sub.2 material, and a dashed line represents the absorption coefficient of a thin layer 2 composed of MgF.sub.2 material, such as is deposited with the aid of the apparatus 1 shown in FIG. 1. In the case of a thin layer composed of MgF.sub.2, the absorption coefficient tails off exponentially toward lower energies in a so-called Urbach tail 18. Below the bandgap energy E.sub.G, which is approximately 12.3 eV, excitonic states are excited, e.g., the 1 s exciton state, in which the absorption coefficient is at a maximum.

[0084] As is likewise discernible in FIG. 2, during the deposition, UV light 11b in a second spectral range 13b is radiated onto the layer 2 or onto the deposited material of the layer 2. The second spectral range 13b typically lies in an energy range of between 75% and 100% of the bandgap energy E.sub.G of MgF.sub.2. In the example shown, the second spectral range 13b lies between 9.84 eV and 11.8 eV, i.e., in an energy range of between 80% and 95% of the bandgap energy E.sub.G of the deposited MgF.sub.2 material. The bandwidth 19 of the second spectral range 13b is thus approximately 1.96 eV, and the mean energy E.sub.M2 of the second spectral range 13b is approximately 10.82 eV. The incidence of UV light 11b in the second spectral range 13b at or just below the band edge energy E.sub.G serves for mobilizing atoms at the surface 2a of the layer 2 of the MgF.sub.2 material.

[0085] The irradiation with UV light 11b in the second spectral range 13b during deposition typically likewise leads to a lower extinction coefficient of the deposited layer 2. A possible mechanism here is the greater ease with which Ehrlich-Schwbel barriers are overcome by the mobilized atoms, which makes it possible to produce larger grains and fewer grain boundaries during the deposition, which leads to a lower extinction coefficient.

[0086] An intensity I.sub.1 of the UV light 11a in the first spectral range 13a must be set such that the rate at which the crystal defects 15 anneal is greater than the generation rate at which new crystal defects 15 arise. The generation rate of defect formation is also correlated with the VUV-driven single-photon processes. If UV light 11b in the second spectral range 13b near the band edge energy E.sub.G of the ionically bonded solid is used for irradiation, it is advantageous to increase the intensity I.sub.1 emitted by the first UV light source 12a in the first spectral range 13a relative to an intensity I.sub.2 of the intensity I.sub.2 emitted by the second UV light source 12b in the second spectral range 13b. The ratio between the intensity I.sub.1 of the UV light 11a in the first spectral range 12a and the intensity I.sub.2 of the UV light 11b in the second spectral range 13b is advantageously more than 3:1, in particular more than 6:1.

[0087] As explained further above, an ion-assisted process and/or a plasma-assisted process may be used for depositing layers 2 having a high density. In the case of ion-assisted deposition, crystal defects 15 are also produced by the ion bombardment. These crystal defects 15 are intended substantially to be annealed by the UV light 11a that is radiated in the first spectral range 13a onto the layer 2. In the case of a plasma-assisted process, it should be taken into consideration that the plasma likewise emits radiation in the UV/VUV wavelength range. FIG. 2 shows, by way of example, the emission spectrum 20 of a plasma for an argon-based RF-pumped cylindrical dielectric barrier discharge process, which was taken from the article VUV emission from a cylindrical dielectric barrier discharge in Ar and in Ar/N.sub.2 and Ar/air mixtures, N. Masoud et al., J. Phys. D 38, 1674-1683 (2005). The radiation of such a plasma, which is generated by the plasma source 9 illustrated in FIG. 1, may likewise cause crystal defects 15 in the layer 2 to be deposited by way of single-photon processes. In this regard, the emission spectrum 20 shown in FIG. 2 overlaps the Urbach tail 18 of the thin MgF.sub.2 layer 2. However, parts of the radiation emitted by the plasma may also have a regenerating effect.

[0088] One or a plurality of layers 2 having a low extinction coefficient and optionally a high density may be deposited onto the substrate 3 in the manner described above. The deposited layers 2 may fulfil various functions, for example a protective function for the substrate 3 or for underlying layers, a reflective function or an antireflective function, etc. The substrate 3 coated with one or a plurality of layers 2 may form an optical element designed for transmitting and/or for reflecting radiation in the VUV wavelength range. Such a transmissive and/or reflective optical element may be used in various optical arrangements for the VUV wavelength range. The reflective optical element may be a mirror, for example, and a transmissive and reflective optical element may be a beam splitter, etc.

[0089] FIG. 5 shows an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus 21. The VUV lithography apparatus 21 includes two optical systems, namely an illumination system 22 and a projection system 23. The VUV lithography apparatus 21 additionally has a radiation source 24, which may be an excimer laser, for example.

[0090] The radiation 25 emitted by the radiation source 24 is conditioned with the aid of the illumination system 22 such that a mask 26, also called a reticle, is illuminated thereby. In the example shown, the illumination system 22 has a housing 32, in which both transmissive and reflective optical elements are arranged. In a representative manner, the illustration shows a transmissive optical element 27, which focuses the radiation 25, and a reflective optical element 28, which deflects the radiation.

[0091] The mask 26 has, on its surface, a structure which is transferred to an optical element 29 to be exposed, for example a wafer, with the aid of the projection system 23, for the purpose of producing semiconductor components. In the example shown, the mask 26 is designed as a transmissive optical element. In alternative examples, the mask 26 may also be designed as a reflective optical element.

[0092] The projection system 22 has at least one transmissive optical element in the example shown. The example shown illustrates, in a representative manner, two transmissive optical elements 30, 31, which serve to, for example, reduce the structures on the mask 26 to the size desired for the exposure of the wafer 29.

[0093] Both in the illumination system 22 and in the projection system 23, a wide variety of transmissive, reflective or other optical elements may be combined with one another in an arbitrary, even more complex, manner. Optical arrangements without transmissive optical elements may also be used for VUV lithography.

[0094] FIG. 6 shows an optical arrangement for the VUV wavelength range in the form of a wafer inspection system 41, but a mask inspection system may also be involved. The wafer inspection system 41 has an optical system 42 with a radiation source 54, from which the radiation 55 is directed onto a wafer 49 via the optical system 42. For this purpose, the radiation 55 is reflected onto the wafer 49 by a concave mirror 46. In the case of a mask inspection system, a mask to be examined could be arranged instead of the wafer 49. The radiation reflected, diffracted and/or refracted by the wafer 49 is directed onto a detector 50 for further evaluation by a further concave mirror 48, which is likewise associated with the optical system 42, via a transmissive optical element 47. The wafer inspection system 41 additionally has 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, one radiation source or a combination of a plurality of individual radiation sources in order to provide a substantially continuous radiation spectrum. In modifications, one or more narrowband radiation sources 54 may also be used.

[0095] At least one of the optical elements 27, 28, 30, 31 of the VUV lithography apparatus 21 shown in FIG. 5 and at least one of the optical elements 46, 47, 48 of the wafer inspection system 41 shown in FIG. 6 are designed as described above. They are thus coated with at least one layer 2 composed of an ionically bonded solid, for example a fluoride or an oxide, wherein the at least one layer 2 was deposited according to the method described further above and/or via the apparatus 1 described further above.

[0096] 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 outside through the laser chamber window 60. The exterior of the laser chamber window 60 is coated with a layer 2 composed of an ionically bonded solid, for example a fluoride layer, which was deposited according to the method described further above and/or via the apparatus 1 described further above. The layer 2 was irradiated with UV/VIS light 11a, 11b during deposition and therefore simultaneously has a high density and a low extinction coefficient. Sealing with such a layer 2 counteracts degradation of the laser chamber window 60 and thus prolongs the lifetime thereof.

[0097] The above description is intended by way of example only. Although the techniques are illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made within the scope and range of equivalents of the claims.