METHOD AND DEVICE FOR FORMING A FLUORIDE OR OXYLFLUORIDE LAYER FOR AN OPTICAL ELEMENT FOR THE VUV WAVELENGTH RANGE, AND OPTICAL ELEMENT COMPRISING SAID FLUORIDE OR OXYLFLUORIDE LAYER

Abstract

Methods of forming a fluoride or oxyfluoride layer for an optical element for use in the VUV wavelength range, which methods comprise: depositing an oxide layer; and converting the oxide layer into the fluoride or oxyfluoride layer by irradiating the oxide layer with UV/VUV radiation in the presence of an active fluorination agent. An optical arrangement has at least one such optical element. An associated device for forming a fluoride or oxyfluoride layer for an optical element is designed for use in the VUV wavelength range.

Claims

1. A method, comprising: depositing an oxide layer on an optical element; and converting the oxide layer into a fluoride or oxyfluoride layer by irradiating the oxide layer with UV/VUV radiation in the presence of an active fluorination agent.

2. The method of claim 1, comprising using physical vapor deposition to deposit the oxide layer on the optical element.

3. The method of claim 1, comprising using chemical vapor deposition to deposit the oxide layer on the optical element.

4. The method of claim 1, wherein the oxide layer is deposited in a coating chamber, and the oxide layer is converted into the fluoride or oxyfluoride layer in a fluorination chamber that is spatially separate from the coating chamber.

5. The method of claim 1, wherein the UV/VUV radiation comprises a first spectral range comprising a wavelength whose energy is at least equal to a dissociation energy of the active fluorination agent.

6. The method of claim 5, wherein a highest energy of the first spectral range is at most 100% greater than the dissociation energy of the active fluorination agent.

7. The method of claim 5, wherein a highest energy of the first spectral range is at most a band gap energy of the fluoride or oxyfluoride layer.

8. The method of claim 5, wherein the UV/VUV radiation comprises a second spectral range in a range of between 75% and 100% of a band gap energy of the fluoride or oxyfluoride layer.

9. The method of claim 1, wherein the UV/VUV radiation comprises a second spectral range in a range of between 75% and 100% of a band gap energy of the fluoride or oxyfluoride layer.

10. The method of claim 1, wherein the UV/VUV radiation or further electromagnetic radiation additionally used to irradiate the fluoride or oxyfluoride layer formed during the conversion comprises a spectral range that at least partly overlaps with an absorption range of at least one crystal defect.

11. The method of claim 1, wherein the oxide layer is irradiated in a protective gas atmosphere.

12. The method of claim 1, wherein the active fluorination agent comprises at least one member selected from the group consisting of F.sub.2, HF, XeF.sub.2, NF.sub.3, CF.sub.4, and SF.sub.6.

13. The method of claim 12, further comprising, before depositing the oxide layer, depositing a further fluoride layer on the substrate of the optical element.

14. The method of claim 1, wherein, when irradiating the oxide layer, a partial pressure of the active fluorination agent lies between 0.05 and 10.sup.6 parts per million by volume.

15. The method of claim 1, wherein the oxide layer comprises a member selected from the group consisting of an MgO layer, an Al.sub.2O.sub.3 layer, an La.sub.2O.sub.3 layer, a Gd.sub.2O.sub.3 layer, a CaO layer, an SrO layer, and a BaO layer.

16. The method of claim 1, wherein the fluoride or oxyfluoride layer comprises a member selected from the group consisting of an MgF.sub.2 layer, an Mg.sub.xO.sub.yF.sub.z layer, an AlF.sub.3 layer, an Al.sub.xO.sub.yF.sub.z layer, an LaF.sub.3 layer, an La.sub.xO.sub.yF.sub.z layer, a GdF.sub.3 layer, a Gd.sub.xO.sub.yF.sub.z layer, a CaF.sub.2 layer, a CaxOvF.sub.z layer, an SrF.sub.2 layer, an Sr.sub.xO.sub.yF.sub.z layer, a BaF.sub.2 layer, and a Ba.sub.xO.sub.yF.sub.z layer.

17. The method of claim 1, further comprising, before depositing the oxide layer, depositing a metallic reflection layer on a substrate of the optical element.

18. An optical element, comprising: a substrate; and a fluoride or oxyfluoride layer prepared according to the method of claim 1, wherein the substrate supports the fluoride or oxyfluoride layer.

19. An optical arrangement, comprising: an optical element, comprising: a substrate; and a fluoride or oxyfluoride layer prepared according to the method of claim 1, wherein the substrate supports the fluoride or oxyfluoride layer.

20. A device, comprising: a fluorination chamber; a supply unit configured to supply inert gas and an active fluorination agent into the fluorination chamber, an inner side of the fluorination chamber being resistant to the active fluorination agent and its conversion products; and a UV/VUV radiation source configured to irradiate an oxide layer of an optical element in the fluorination chamber with UV/VUV radiation in the presence of an active fluorination agent in the fluorination chamber to convert the oxide layer into the fluoride or oxyfluoride layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Exemplary embodiments are shown in the schematic drawing and are explained in the description which follows.

[0065] FIG. 1 shows a schematic illustration of three snapshots of a method in which a dense oxide layer is deposited and converted into a fluoride or oxyfluoride layer by subsequent irradiation with VUV radiation in the presence of an active fluorination agent.

[0066] FIG. 2 shows a schematic illustration of the absorption and spectral ranges relevant to the irradiation of the oxide layer.

[0067] FIG. 3 shows a schematic illustration of a device for forming the fluoride or oxyfluoride layer by converting the oxide layer in the presence of the active fluorination agent.

[0068] FIGS. 4A and 4B show the formation enthalpies or the difference between the formation enthalpies of three selected oxides and fluorides.

[0069] FIGS. 5A and 5B show two examples of a procedure for producing an optical element for reflecting VUV radiation by the method presented in FIG. 1.

[0070] FIG. 6 shows a schematic illustration of an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus.

[0071] FIG. 7 shows a schematic illustration of an optical arrangement for the VUV wavelength range in the form of a wafer inspection system.

DETAILED DESCRIPTION

[0072] FIG. 1 shows a schematic illustration of the formation of a fluoride or oxyfluoride layer 1 of an optical element 2 for use in the VUV wavelength range. Three snapshots M1, M2, M3 of a substrate 3 of the optical element 2 are depicted during the formation of the fluoride or oxyfluoride layer 1.

[0073] The first snapshot M1 depicted to the left in FIG. 1 shows the substrate 3 following the deposition of a dense oxide layer 4, which consists of MgO in the example shown. The dense oxide layer 4 is deposited by a PVD deposition process known per se, for example by sputter deposition, for example magnetron sputtering, ion beam sputtering (IBS), ion beam-assisted sputtering (IBAS) or plasma ion-assisted deposition (PIAD). Deposition in a CVD deposition process, which may for example comprise an atomic layer deposition process (ALD) or a plasma-enhanced atomic layer deposition process (PEALD), is also possible.

[0074] The oxide layer 4 is deposited in a coating chamber that is not shown pictorially in FIG. 1. The substrate 3 with the deposited oxide layer 4 is taken from the coating chamber and transferred to a fluorination chamber (likewise not shown pictorially in FIG. 1), as indicated by an arrow in FIG. 1.

[0075] The second snapshot M2 depicted in the center of FIG. 1 shows the oxide layer 4, more precisely a surface 5 of the oxide layer 4 facing the surroundings, during the irradiation with UV/VUV radiation 6 in the presence of an active fluorination agent FW. As a consequence of the irradiation, the active fluorination agent FW dissociates and forms fluorine species F, F.sub.2, F*. The fluorine species F, F.sub.2, F* react with the oxide of the oxide layer 4 present at the surface 5 and convert the oxide into a fluoride (MgF.sub.2 in the present case). By way of example, the active fluorination agent FW is NF.sub.3, but it may also be a different substance that is able to provide the fluorine species F, F.sub.2, F* by way of photodissociation, for example at least one substance from the group comprising: F.sub.2, HF, XeF.sub.2, CF.sub.4 and SF.sub.6.

[0076] The third snapshot M3 depicted to the right in FIG. 1 shows a fluoride layer 1, into which the oxide layer 4 was converted during the fluorination. The fluoride layer 1 is an (at least approximately) stoichiometric fluoride. The optical performance of the optical element 2 is improved significantly by the conversion of the dense oxide layer 4 into the fluoride layer 1. Unlike what was described above, an oxyfluoride layer, rather than the fluoride layer 1, may be formed during the conversion. This occurs when not all of the oxide in the oxide layer is converted into a fluoride. The degree of conversion of the oxide in the oxide layer 4 into a fluoride depends on various influencing factors, inter alia on the thickness of the oxide layer 4 and the duration of irradiation.

[0077] Furthermore, the fluoride layer 1 is irradiated by further electromagnetic radiation 7 during the aftertreatment in the example illustrated, but this is not mandatory. This serves the annealing of crystal defects 8 in the fluoride layer 1. In an alternative to that or in addition, the irradiation by the further electromagnetic radiation 7 may occur during the irradiation of the oxide layer 4, for the purpose of annealing crystal defects 8 in the already converted portion of the fluoride layer 1.

[0078] Moreover, the oxide layer 4 may additionally be heated during the irradiation, although this is not depicted in FIG. 1. However, heating is not a mandatory constituent of the method.

[0079] FIG. 2 illustrates the absorption and spectral ranges relevant to the irradiation of the oxide layer 4. Energy is plotted on the abscissa axis, and the absorption cross section is plotted on the ordinate axis. The dissociation energy E.sub.diss of the active fluorination agent FW, the absorption cross section 12 of the fluoride or oxyfluoride layer 1 to be newly formed, including an Urbach tail 12, and the absorption cross section 13 of a crystal defect 10 in the fluoride or oxyfluoride layer 1 are depicted schematically.

[0080] The UV/VUV radiation 6 used to irradiate the oxide layer 4 has a first spectral range 14 for the photodissociation of the active fluorination agent FW. By way of example, the first spectral range 14 comprises at least one wavelength whose energy E.sub.ph is at least equal to the dissociation energy E.sub.diss of the active fluorination agent FW.

[0081] Further, the highest energy E.sub.UP of the first spectral range 14 here is less than 50% greater than the dissociation energy E.sub.diss of the active fluorination agent FW (i.e. less than 1.5E.sub.diss; cf. FIG. 2); this is exemplary and not mandatory. This suppresses potentially negative and/or competing effects. The highest energy E.sub.UP of the first spectral range 14 may also be no more than the band gap energy EG of the oxide layer 4, such as no more than 75% of the band gap energy EG of the oxide layer 4.

[0082] Moreover, the fluoride or oxyfluoride layer 1 is irradiated with further electromagnetic radiation 7 by way of example, this serving the annealing of at least one crystal defect 10 in the fluoride or oxyfluoride layer 1. To this end, the further electromagnetic radiation 7 includes a spectral range 16 that overlaps with the absorption range 17 of the at least one crystal defect 10. In the illustrated example, the spectral range 16 of the further electromagnetic radiation 9 lies within the absorption range 17 of the crystal defect 8, which is an F center; however, this is not necessarily required. In an alternative to that, the UV/VUV radiation 6 may also include a corresponding spectral range.

[0083] In the illustrated example, the spectral range 16 of the further electromagnetic radiation 9 comprises the absorption energy E.sub.A of the crystal defect 10 at which the absorption cross section is maximal. However, this is not necessarily the case. The absorption range 17 of the crystal defect 10 is defined by a drop to one hundredth of the maximum value of the absorption cross section (FWHM) at the absorption energy E.sub.A of the crystal defect 10. Further, it is desirable if a mean energy E.sub.m (arithmetic mean) of the spectral range 16 deviates from the absorption energy E.sub.A of the crystal defect 10 by no more than 0.5 eV, for example by no more than 0.25 eV.

[0084] Moreover, the UV/VUV radiation 8 includes a second spectral range 18 for mobilizing atoms at the surface 5, at the grain boundaries 5 and/or in the grain volume 5 of the fluoride or oxyfluoride layer 1 to be newly formed, which correspond to the grain boundaries 5 and the grain volume 5 of the oxide layer 4. In the illustrated example, this second spectral range 18 lies in an energy range of between 75% and 100% of the band gap energy E.sub.G of the fluoride or oxyfluoride layer 1. The second spectral range 18 may also lie between 80% and 95% of the band gap energy E.sub.G of the fluoride or oxyfluoride layer 1.

[0085] FIG. 3 shows a device 60 for forming the fluoride or oxyfluoride layer 1 of the optical element 2 from FIG. 1 by converting the oxide layer 4 into the fluoride or oxyfluoride layer 1. The device 60 comprises a fluorination chamber 61, supply unit 62 and a UV/VUV radiation source 63.

[0086] The optical element 2 that comprises the oxide layer 4, which is applied to a substrate 3 in exemplary fashion in this case, is attached to a substrate holder 64, which is rotatable about a rotation axis 65, within the fluorination chamber 61. However, deviating from the example illustrated here, the device 60 need not comprise a rotatable substrate holder 64.

[0087] The supply unit 62 serves to supply protective gas, which is in the form of inert gas IG, and the active fluorination agent FW into the fluorination chamber 61, the supply unit 62 comprising a first valve 66 for controlled supply of the inert gas IG and a second valve 67 for controlled supply of the active fluorination agent FW. The second valve 67 is a controllable metering valve. As a consequence, the oxide layer 4 may be irradiated in the presence of the active fluorination agent FW in a protective gas atmosphere within the fluorination chamber 61. The device 60 moreover comprises a gas outlet 68 for letting out the inert gas IR and reaction products formed during the fluorination. In the example illustrated, the inert gas IR is argon, but it is also possible to use other inert gases IR, for example other light noble gases such as helium or neon. Mixtures of noble gases, for example of the noble gases mentioned, can also be used as inert gas IR.

[0088] The UV/VUV radiation source 63 serves to irradiate the oxide layer 4 with UV/VUV radiation 6 in the presence of the active fluorination agent FW in the fluorination chamber 61. By way of example, in the illustrated example, the UV/VUV radiation 6 enters the fluorination chamber 61 through an MgF.sub.2 window 69. The VUV radiation source 63 serves to generate UV/VUV radiation 6 in the above-described first spectral range 14.

[0089] Moreover, by way of example, the device 60 in this case comprisesalthough this is not mandatorya second UV/VUV radiation source 70 for irradiating the oxide layer 4 with UV/VUV radiation 7 in the above-described second spectral range 18 for mobilizing atoms at the surface 5, at the grain boundaries 5 and/or in the grain volume 5 of the oxide layer 4. In the illustrated example, the UV/VUV radiation 7 from the second UV/VUV radiation source 70 enters the fluorination chamber 61 through an MgF.sub.2 window 69. The device 60 also comprises a further radiation source 71 for irradiating the fluoride or oxyfluoride layer 1, formed during the conversion, with further electromagnetic radiation 7 in the spectral range 17, described above in the context of FIG. 2, for annealing at least one crystal defect 10 in the fluoride or oxyfluoride layer 1. The further electromagnetic radiation 7 from the further radiation source 71 enters the fluorination chamber 61 through a further MgF.sub.2 window 69.

[0090] In place of at least one of the MgF.sub.2 windows 69, 69, 69, it is possible in principle to also use windows made of other materials, for example from CaF.sub.2, SrF.sub.2 and/or BaF.sub.2, with sufficient transparency at the utilized wavelengths being decisive in this respect.

[0091] The fluorination chamber 61 may be sealed in a gas-tight manner. Furthermore, the inner side 72 of the fluorination chamber 61 is resistant to the active fluorination agent FW and its conversion products. For this purpose, in the example illustrated, the fluorination chamber 61, at least on its inner side 72, is formed from a metal in the form of Monel steel, which forms a passivating layer in order to prevent corrosion. In principle, the fluorination chamber 61 can also be formed from other corrosion-resistant metals if the latter are free of Cr and Ti.

[0092] Alternatively, a corrosion-resistant coating, e.g. composed of NiP, Pt or Ru/Rh mixtures, can be applied to the inner side 72 of the fluorination chamber 61. The corrosion-resistant coating can be applied to the inner side 72 of the fluorination chamber 61 via a galvanic process, for example. The components which are arranged in the fluorination chamber 61 and which come into contact with the active fluorination agent FW are likewise resistant to the active fluorination agent FW and the conversion products thereof.

[0093] Further the device 60 depicted here comprises, by way of example but not necessarily, a sensor 73 for measuring the oxygen concentration c.sub.O2 in the fluorination chamber 61 and a further sensor 74 for measuring the H.sub.2O concentration c.sub.H2O in the fluorination chamber 61.

[0094] By way of example, the oxygen concentration c.sub.O2 in the fluorination chamber 61 is less than 50 ppbV during the irradiation of the oxide layer 4 or the conversion. The oxygen concentration c.sub.O2 should be as low as possible, although it may also be greater than 50 ppbV. However, it is desirable for the oxygen concentration c.sub.O2 to be less than 10 ppmV, such as less than 1 ppmV, for example less than 100 ppbV.

[0095] Further, in the illustrated example, the H.sub.2O concentration c.sub.H2O in the fluorination chamber 61 is less than 100 ppbV during the irradiation of the oxide layer 4. In principle, the H.sub.2O concentration c.sub.H2O in the fluorination chamber 61 during the irradiation of the oxide layer 4 should be as low as possible, although the H.sub.2O concentration c.sub.H2O may also be greater than 100 ppbV. However, it is desirable for the H.sub.2O concentration c.sub.H2O to be less than 10 ppmV, such as less than 1 ppmV, for example less than 500 ppbV.

[0096] Although this is not mandatory, the device 60 of the illustrated example moreover comprises a sensor 75 for measuring the partial pressure c.sub.FW of the active fluorination agent FW in the fluorination chamber 61 and a closed-loop controller 76 for adjusting the partial pressure c.sub.FW of the active fluorination agent FW in the fluorination chamber 61 to a target value, the control being implemented via the actual measured value M from the sensor 75 for measuring the partial pressure crw of the active fluorination agent FW in the fluorination chamber 61 and via the control of the second valve 67. The sensor 75 may be designed to measure only the partial pressure cow of the active fluorination agent FW; however, it may also be a residual gas analyzer that is able to also determine the partial pressures of other gases contained in the fluorination chamber 21. It is possible that such a residual gas analyzer assumes the function of the three sensors 73, 74, 75 depicted in FIG. 3. If the second valve 67 is a metering valve, for example a mass flow regulator, then it is possible to dispense with the use of the sensor 75 for measuring the partial pressure c.sub.FW of the active fluorination agent FW in the fluorination chamber 61.

[0097] The active fluorination agent FW is added to the inert gas IR in the supply unit 62. The partial pressure c.sub.FW of the active fluorination agent FW in the aftertreatment chamber 61 lies typically between 0.05 and 10.sup.6 ppmV, such as between 0.075 ppmV and 50 ppmV, for example between 0.1 ppmV and 10 ppmV, during the irradiation of the oxide layer 4.

[0098] In principle, the chemically and energetically driven conversion of an oxide into a fluoride works particularly well whenever the fluoride M.sub.xF.sub.y(M=metal, F=fluorine) is more stable than the oxide M.sub.aO.sub.b. FIG. 4A shows, by way of example, the formation enthalpy (in kJ/mol) for the three substance pairs MgO/MgF.sub.2, Al.sub.2O.sub.3/AlF.sub.3 and La.sub.2O.sub.3/LaF.sub.3. FIG. 4B shows the difference between the formation enthalpy .sub.fH.sup.0.sub.ox of the oxide and the formation enthalpy .sub.fH.sup.0.sub.fl of the corresponding fluoride for the three chemical elements Mg, Al and La. For a positive value of the difference .sub.fH.sup.0.sub.ox.sub.fH.sup.0.sub.fl, the fluoride of the respective substance pair is more stable than the oxide. As evident from FIG. 6b, this is only the case for Mg from among the three elements shown, i.e. for Mg there is a pronounced driving force to convert the oxide into the corresponding fluoride. Experiments have demonstrated a significant reduction in extinction for Al.sub.2O.sub.3, too, following the above-described fluorination step. Evaluation of the experiments suggests that the conversion of Al.sub.2O.sub.3 to AlF.sub.3 works slightly less wellin agreement with the prediction from the formation enthalpiesthan the conversion of MgO to MgF.sub.2. The conversion of other oxides to fluorides or oxyfluorides is also possible, for example the conversion of Gd.sub.2O.sub.3 to GdF.sub.3, of CaO to CaF.sub.2, of SrO to SrF.sub.2 or of BaO to BaF.sub.2.

[0099] The method described above in the context of FIG. 1 may find use for the production of different optical elements. Two examples for the production of an optical element 2 in the form of a mirror that reflects radiation in the VUV wavelength range in broadband fashion are described below on the basis of FIG. 5A and FIG. 5B.

[0100] In the example shown in FIG. 5A, the substrate 3 is introduced into a coating chamber 59 in order to perform a coating process, in which, in a first step, a metallic reflection layer in the form of an aluminum layer 10 is deposited on the substrate 3 by a conventional deposition method. In a subsequent step on the aluminum layer 10, the dense oxide layer 4 described in the context of FIG. 1 is deposited on the aluminum layer 10 via a plasma-assisted coating method (see above).

[0101] Since the aluminum layer 10 is protected from environmental influences by the oxide layer 4, the substrate 3 with the deposited aluminum layer 10 and the oxide layer 4 may be taken from the coating chamber 59 and introduced into the fluorination chamber 61, which is part of the device 60 shown in FIG. 3. The fluorination process which is described in the context of FIG. 3, which follows the coating process and in which the oxide layer 4, e.g. in the form of an MgO layer, is converted into the fluoride or oxyfluoride layer 1 takes place in the fluorination chamber 61.

[0102] In the example shown in FIG. 5B, the deposition of the dense oxide layer 4 is preceded by the deposition of a (further) fluoride layer 11, possibly made e.g. of MgF.sub.2, on the aluminum layer 10. A comparatively thin, dense oxide layer 4 is deposited on the fluoride layer 11, as described in the context of FIG. 1. In a manner analogous to the example described in FIG. 5A, the substrate 3 is taken from the coating chamber 59 and transferred into the fluorination chamber 61, in which the fluorination process for converting the oxide layer 4 into a fluoride layer 1 takes place. In the example described in FIG. 5B, the oxide layer 4, which is deposited on the further fluoride layer 11, is comparatively thin, typically 5-10 nm, and is therefore, unlike the example described in FIG. 5A, converted not into an oxyfluoride layer but into a fluoride layer 1. However, the oxide layer 4 may also have a thicker embodiment.

[0103] The above-described optical element 2, which comprises the fluoride or oxyfluoride layer 1, may be used in different optical arrangements for the VUV wavelength range.

[0104] FIG. 6 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, namely an illumination system 22 and a projection system 23. The VUV lithography apparatus 21 additionally comprises a radiation source 24, which may be an excimer laser, for example.

[0105] 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 comprises 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.

[0106] The mask 26 comprises, 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 transmissive optical element. In alternative embodiments, the mask 26 may also be designed as reflective optical element.

[0107] The projection system 22 comprises at least one transmissive optical element in the example illustrated. The example shown illustrates, in a representative manner, two transmitting optical elements 30, 31, which serve, for example, to reduce the structures on the mask 26 to the size desired for the exposure of the wafer 29.

[0108] Both in the illumination system 22 and in the projection system 23, a wide variety of transmissive, reflective or other optical elements can be combined with one another as desired, including in a more complex manner. Optical arrangements without transmissive optical elements can also be used for VUV lithography.

[0109] FIG. 7 shows an optical arrangement for the VUV wavelength range in the form of a wafer inspection system 41, but this may also be a mask inspection system. The wafer inspection system 41 comprises 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 off a concave mirror 46 to the wafer 49. In the case of a mask inspection system, it would be possible to replace the wafer 49 with a mask to be examined. 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 comprises a housing 52, in which the two mirrors 46, 48 and the transmissive optical element 47 are arranged. The radiation source 54 may, for example, be exactly one radiation source or a combination of a plurality of individual radiation sources in order to provide a substantially continuous radiation spectrum. In modifications, it is also possible to use one or more narrowband radiation sources 54.

[0110] At least one of the optical elements 27, 28, 30, 31 of the VUV lithography apparatus 21 shown in FIG. 6 and at least one of the optical elements 46, 47, 48 of the wafer inspection system 41 shown in FIG. 7 are designed here as described above. The at least one of the optical elements 27, 28, 30, 31, 46, 47, 48 thus comprises (at least) one fluoride or oxyfluoride layer that was formed or produced by the above-described method.