DE102011054427A1 - Method for manufacturing optic element e.g. lens, in UV wavelength range, involves attaching porous layer by commonly applying two inorganic materials, and removing one of materials so that pores are formed in unremoved material - Google Patents

Abstract

The method involves providing an antireflection coating (51) with a layer made of porous material. A porous layer (56) is attached by commonly applying two inorganic materials. One of the materials is removed so that pores are formed in unremoved material. Two layers are attached on a substrate (50) as the antireflection coating. The inorganic materials are simultaneously applied or as alternating thin layers. Refraction indexes of layers of a partial layer system (52) are smaller than refraction indexes of layers of another partial layer system. An independent claim is also included for an optic element.

Description

The present invention relates to a method for producing an optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating comprising at least one layer of porous material. Furthermore, the invention relates to such optical elements.

For better utilization of existing radiation intensity by optical elements in the ultraviolet, but also visible or near-infrared wavelength range, optical elements are usually provided with antireflection coatings. These can be single-layered or multi-layered. Particularly in the case of multilayer antireflection coatings, it is possible to use layer systems composed of alternatingly arranged layers of materials which are higher or lower in the wavelength range used. One approach is to reduce the total reflection through destructive interference of the partial beams reflected at ply boundaries. Another approach is to provide a porous, typically single-layer anti-reflection coating to achieve a refractive index as close as possible to the refractive index of the surrounding medium. Such porous layers are usually prepared by sol-gel processes. The optical elements may be, for example, lenses, beam splitters, windows or prisms.

From the WO 2008/148462 A1 It is known to provide an anti-reflection surface on an optical element for the ultraviolet wavelength range by etching nanostructures into the substrate surface of the optical element, omitting etch masks. In further variants, the substrate surface can first be coated and the nanostructure etched into the coating. The nanostructure leads to a reduction in the density of the material and thus to a reduction in the effective refractive index. Particularly preferably, the etching is carried out by plasma etching or ion beam etching. It has proven to be advantageous to carry out a plasma-supported anisotropic etching in a suitable gas atmosphere.

It is an object of the present invention to provide a further possibility of producing an ultraviolet wavelength optical element with antireflection coating, in particular with at least one porous layer.

This object is achieved by a method for producing an optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating comprising at least one layer of porous material, wherein the porous layer is applied by applying two inorganic materials together and then one of the materials is removed, so that pores are formed in the material not removed.

It has been found that the co-application of two inorganic materials, which can be removed differently well, to form a porous layer by choosing the ratio of the two materials to each other control the pore content and thus the resulting refractive index of this layer quite easily with relatively little effort leaves. It is of great advantage that, surprisingly, porous inorganic layers can be produced directly and organic materials can be completely dispensed with. Particularly in the case of shorter-wave ultraviolet radiation and at higher radiation intensities in the ultraviolet wavelength range, it is not possible to use organic materials on optical elements, since they in particular strongly absorb ultraviolet radiation and are not long-term stable.

The application of the two materials can take place via any method of chemical vapor deposition (CVD method) or physical vapor deposition (PVD method) or combinations thereof in a conventional manner known in the art. During the subsequent removal of the one material, small to very small cavities are formed in the material not removed, so that the resulting layer of material which has not been removed is porous and has a lower refractive index at the same wavelength than if it were not porous. Due to the co-application of the two materials, the pores in the resulting porous layer are more evenly distributed than, for example, the plasma deposited nanostructures, which often have a more columnar structure and are very sensitive unlike the porous layers made by the method proposed herein. so they can not be cleaned by wiping, for example.

It should be noted that here and in the following of two applied materials is mentioned, but this is not to be understood as exactly two materials. Depending on the choice of material for the resulting porous layer, for example, if it is not a pure substance, but a compound, it may be advantageous if this compound is formed only by applying the necessary individual components. Likewise, this may apply to the material to be removed, especially if certain compounds or mixtures are particularly easy to remove.

In preferred embodiments, as antireflection coating, at least two layers are applied to a substrate, and the layer furthest from the substrate is applied as a porous layer, wherein as material not to be removed, one in the wavelength range of the optical element, i. In the wavelength range for which the optical element is designed, low refractive index material is applied. Thus, a conventional single or multi-layer antireflection coating of non-porous material can be further improved in its antireflection effect by providing at least one porous layer at the interface to the surrounding medium, since the at least one porous layer has a particularly low refractive index and thereby a particularly effective Antireflection effect by destructive interference or by a gradual transition of the refractive index from the substrate on the conventional antireflection coating to the surrounding medium, ie e.g. Vacuum or air allowed.

Advantageously, the two inorganic materials are applied simultaneously or as alternating thin layers. In simultaneous application, both materials are applied simultaneously, in particular vapor-deposited by CVD and / or PVD processes, so that a mixed layer of both materials is formed. Alternatively, it has proven useful to apply the two materials as alternating thin layers, in particular vapor-deposited by CVD and / or PVD methods, the layers should be so thin that forms by interdiffusion at the interfaces also a mixed layer of both materials ,

Preferably, the material to be removed is removed chemically or chemically-physically. In chemical processes, in particular wet-chemical processes are preferred, for example the use of water as solvent. As a result, the effort when removing the one material is kept very low. When wet-chemical removal processes are used, the two materials are advantageously selected in particular according to their different solubilities. In chemical-physical processes, in particular dry etching processes, for example reactive ion etching or plasma etching, are used. When dry etching methods are used, the two materials are advantageously chosen, in particular, for having different etching rates for the selected dry etching method. It is also particularly advantageous to also select the two materials according to that both have a rather lower refractive index in the wavelength range in which the optical element is to be used. This has proven particularly useful in porous layers, in which the one material targeted or procedural reasons is not completely removed.

In a further aspect, this object is achieved by an optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating comprising at least one layer of porous material, which is prepared by the described method.

In particular, by u.a. this method produces an optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range whose antireflection coating comprises a first part-layer system of non-porous layers of materials which alternate in the wavelength range of the optical element higher and lower refractive materials on one substrate and a second, from the substrate further removed part-layer system of one or more porous layers, wherein the at least one porous layer is based on a lower refractive in the wavelength range of the optical element material.

The first part-layer system is a conventional antireflection coating without porous layers made by conventional coating techniques. In addition, the second part-layer system is applied from at least one porous layer so that the difference between the resulting refractive index of the first part-system and the refractive index of the surrounding medium in the wavelength range of the optical element is reduced, which additionally reduces the reflection at the interface with the surrounding medium. Thus, a conventional single or multi-layer antireflection coating of non-porous material can be further improved in its antireflection effect by providing at least one porous layer at the interface with the surrounding medium since the at least one porous layer has a particularly low refractive index and thereby a gradual transition the refractive index of the substrate over the resulting refractive index of the conventional single or multilayer antireflection coating allows to the refractive index of the surrounding medium.

The second ply system preferably has two or more porous layers, the refractive index of the porous layers arranged closest to the substrate being at the highest of all porous layers and the refractive index of each further porous layer being continuously lower. As a result, a steadily decreasing refractive index gradient approaches as closely as possible to the surrounding medium, which has a positive effect on the suppression of the reflection at the interface from the optical element to the surrounding medium.

It has proven to be advantageous if the optical thickness of the second part-system is less than half the wavelength for which the optical element is designed. This can avoid that the second partial system may lead to increased absorption, which could affect the desired high transmission as too high a reflection.

The refractive indices of the layers of the second part-system are preferably smaller than the refractive indices of the layers of the first part-system. This has proven particularly useful in ambient media such as vacuum or air, where the refractive index is close to 1, since normal inorganic material layers without pores in the wavelength ranges of the optical element, especially if it is in the ultraviolet, have a refractive index of significantly greater than 1. In this way, a gradual transition of the refractive index to the surrounding medium can be approximated particularly well.

In preferred embodiments, the first part-layer system has no more than one layer whose refractive index in the wavelength range of the optical element is greater than 1.25 times the refractive index of the substrate. For optical elements which are designed for wavelengths less than about 250 nm, the first part-layer system preferably has no more than one layer whose refractive index in the wavelength range of the optical element is greater than the refractive index of the substrate. As a result, it is possible to obtain particularly broadband antireflection coatings which are also broadband over large incident angle intervals, as well as narrowband antireflection coatings which retain their effect even at very large angles of incidence.

Advantageously, the first part-layer system comprises as higher-refractive-index material one or more of lanthanum fluoride, gadolinium fluoride, neodymium fluoride, ytterbium fluoride, aluminum oxide, hafnium oxide, zirconium oxide, niobium oxide, scandium oxide, ytterbium oxide, lanthanum oxide, tantalum oxide and as lower refractive material one or more of the group aluminum fluoride, Chiolite, cryolite, sodium fluoride, magnesium fluoride, lithium fluoride, silica, yttrium fluoride, calcium fluoride, barium fluoride. Based on these materials, antireflection coatings with particularly good reflection suppression can be obtained.

Advantageously, the optical element or the second partial layer system as the material of the one or more porous layers of magnesium fluoride and / or silicon dioxide. Magnesium fluoride and silicon dioxide have particularly low refractive indices not only in the ultraviolet, visible and near-infrared wavelength range, in particular between 180 nm and 800 nm, but can be handled particularly easily both during application and during removal.

The present invention will be explained in more detail with reference to a preferred embodiment. Show this

1 to 4 Flowcharts for four different embodiments of the proposed method for the production of optical elements for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an anti-reflection coating having at least one layer of porous material;

5a , b a first and a second embodiment of an optical element;

6a -E percent reflection at 193 nm versus angle of incidence for s-polarized radiation, p-polarized radiation and unpolarized radiation in various embodiments of an optical element;

7a -E the reflection for unpolarized radiation in the wavelength range of 200 to 400 nm for different angles of incidence in various embodiments of an optical element;

8a F the reflection for unpolarized radiation in the wavelength range between 380 nm and 750 nm for different angles of incidence in different embodiments of the optical element;

9a -E the reflection for unpolarized radiation in the wavelength range between 750 nm and 1400 nm for different angles of incidence in different embodiments of an optical element; and

10a -E the reflection for unpolarized radiation in the wavelength range between 250 nm and 500 nm for different angles of incidence in various embodiments of an optical element.

In 1 is a first embodiment for carrying out the method for producing optical elements for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating having at least one layer of porous material, shown schematically. In a first step 101 For example, a first part-layer system which already has reflection-suppressing properties was applied by conventional coating methods. In a further step 103 At temperatures of about 250 ° C and a pressure of 1 × 10 ^-6 mbar to 5 × 10 ^-4 mbar magnesium fluoride and silicon dioxide were vapor-deposited simultaneously on the surface of the first part-system. As the mixing ratio, a ratio of the vapor deposition rates was set at which 0.25 to 1.0 part of silica came for one part of magnesium fluoride. Thus, an MgF 2 / SiO 2 mixed layer having an SiO 2 content of about 20% by volume to 50% by volume was produced. The content of one or the other of the mixed layer can be estimated by GX = R2 / (R1 + R2), where GX is the volume fraction of material X where X is 1 or 2 and R1 and R2 are the vapor deposition rates of materials 1 and 2, respectively.

In a subsequent step 105 The silica contained in the resulting mixed layer was dissolved out by a dry etching method to form a porous magnesium fluoride layer. Preferably, an isotropic etching process is used. For example, plasma etching with tetrafluoromethane as the etching gas has proven itself. A magnesium fluoride layer produced in this way with a pore content of 20% by volume exhibits, for example, a refractive index of about 1.32 at a wavelength of 266 nm. The porosity can be increased by a higher silicon dioxide content in the mixed layer or at an already higher silicon dioxide content by a more complete removal of the silicon dioxide from the magnesium fluoride matrix and thus further reduce the refractive index.

In 2 is a second embodiment for carrying out the method for producing optical elements for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating having at least one layer of porous material, shown schematically. In a first step 201 For example, a first part-system which already has reflection-suppressing properties has also been applied by conventional coating methods. In a further step 203 were at temperatures of about 250 ° C and a pressure of 1 · 10 ^-6 mbar to 5 · 10 ^-4 mbar sodium fluoride and silicon dioxide vapor-deposited simultaneously on the surface of the first part-system. As a mixing ratio, a ratio of the vapor deposition rates was set at which 0.4 to 1.5 parts of sodium fluoride came to one part of silica. Thus, an SiO 2 / NaF mixed layer having a NaF content of about 29% by volume to 60% by volume was produced.

In a subsequent step 205 From the resulting mixed layer, the sodium fluoride content was removed wet-chemically. As a solvent, water has been proven. The dissolution rate can be increased by heating the solvent. It has also been beneficial to continuously supply pure solvent, for example demineralized water, in order to avoid saturation of the solvent with the material to be dissolved out. A porous silica sheet thus prepared having a pore content of 36% by volume has a refractive index of 1.32 at 266 nm. The refractive index can be influenced via the pore fraction. For this purpose, the sodium fluoride content and / or the degree of removal of the sodium fluoride portion can be varied.

In 3 is a third embodiment for carrying out the method for producing optical elements for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating having at least one layer of porous material, shown schematically. In a first step 301 For example, a first part-layer system which already has reflection-suppressing properties was applied by conventional coating methods. In a further step 303 At temperatures of about 250 ° C and a pressure of 1 × 10 ^-6 mbar to 5 × 10 ^-4 mbar magnesium fluoride and silicon dioxide were vapor-deposited alternately as thin individual layers. The ratio of the individual layer thicknesses of magnesium fluoride to silicon dioxide was 1: 0.25 to 1: 1. The individual layer thicknesses were chosen so that they were in the order of the roughness depth of the respective interfaces. Typically they are in the subnanometer range. As a result, a sufficient mixing of the single layer sequence to a mixed layer is achieved. In the present example, the thickness of the magnesium fluoride layers was set to be about 0.5 nm and that of the silica layers to be correspondingly thinner.

In a subsequent step 305 The silica contained in the resulting mixed layer was dissolved out by a dry etching method to form a porous magnesium fluoride layer. Preferably, an isotropic etching process is used. For example, plasma etching with tetrafluoromethane as the etching gas has proven itself. A magnesium fluoride layer produced in this way with a pore content of 20% by volume exhibits, for example, a refractive index of about 1.32 at a wavelength of 266 nm. The porosity can be increased by a higher silicon dioxide content in the mixed layer or at an already higher silicon dioxide content by a more complete removal of the silicon dioxide from the magnesium fluoride matrix and thus further reduce the refractive index.

In 4 is a fourth embodiment for carrying out the method for producing optical elements for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating having at least one layer of porous material, shown schematically. In a first step 401 For example, a first part-layer system which already has reflection-suppressing properties was applied by conventional coating methods. In a further step 403 were at temperatures of about 250 ° C and a pressure of 1 · 10 ^-6 mbar to 5 · 10 ^-4 mbar sodium fluoride and silicon dioxide vapor deposited as thin individual layers alternately. The ratio of the individual layer thicknesses of silicon dioxide to sodium fluoride was 1: 0.4 to 1: 1.5. The individual layer thicknesses were chosen so that they were in the order of the roughness depth of the respective interfaces. Typically they are in the subnanometer range. As a result, a sufficient mixing of the single layer sequence to a mixed layer is achieved. In the present example, the thickness of the silicon dioxide layers was set to be about 0.5 nm and that of the sodium fluoride layers to be correspondingly thinner.

In a subsequent step 405 From the resulting mixed layer, the sodium fluoride content was removed wet-chemically. As a solvent, water has been proven. The dissolution rate can be increased by heating the solvent. It has also been beneficial to continuously supply pure solvent, for example demineralized water, in order to avoid saturation of the solvent with the material to be dissolved out. A porous silica sheet thus prepared having a pore content of 36% by volume has a refractive index of 1.32 at 266 nm. The refractive index can be influenced via the pore fraction. For this purpose, the sodium fluoride content and / or the degree of removal of the sodium fluoride portion can be varied.

It should be noted that the choice of inorganic materials magnesium fluoride and silicon dioxide or silicon dioxide and sodium fluoride is only an example. As the matrix material not to be removed, any inorganic material is suitable which, with its refractive index in the wavelength range of the optical element, lies between the refractive index of the optical element without porous layer and the refractive index of the medium surrounding the optical element in use in the wavelength range used. As the inorganic material to be removed, any material that has a higher removal rate than the non-removable material by wet-chemical or dry-etching process is suitable.

With the previously in conjunction with the 1 to 4 described methods can be prepared in which directly on the substrate one or more porous layers are applied, optionally also in conjunction with non-porous layers. In particularly preferred embodiments, optical elements as in the 5a and b are shown. For their preparation can be made of conventional methods for the preparation of porous layers.

The in the 5a and b illustrated optical elements 5 have in common that on a substrate 50 a part-day system 52 an anti-reflection coating 51 from non-porous layers 54 . 55 is applied, the materials and layer thicknesses are selected according to that the least possible reflection on the corresponding surface of the optical element is caused. In particular, higher and lower breaking layers alternate 54 . 55 from. Depending on the embodiment variant, the position closest to the substrate as well as the position farthest from the substrate may be low or higher-refractive. In the example shown here is an even number of non-porous layers 54 . 55 shown. In other variants, their number can also be odd. In addition, the non-porous part-system can 52 also have layers of not only two, but three, four, five or more materials.

It should be noted that in the 5a and b only one surface of the optical element each 5 is shown. Is the optical element 5 formed as a lens, for example, are two opposing surfaces with an antireflection coating described herein 51 Mistake. At prisms and For example, beam splitters may have three surfaces with an antireflection coating described herein 51 be provided.

The optical element 5 out 5a points to that of the substrate 50 distant side of the part-system 52 a porous layer 56 on. This in 5b illustrated example of an optical element 5 points to that of the substrate 50 distant side of the part-system 52 three porous layers 56a -C on. Other variations may be two, four, five, six or more porous layers. As shown below by means of concrete examples, the porous partial system allows 53 from one or more porous layers on the conventional, non-porous part-system 52 be achieved that not only the total reflection for desired wavelength ranges and / or angle of incidence decreases. The splitting into s-polarized and p-polarized radiation also becomes significantly lower, ie the reflection depends less on the polarization state of the radiation than on optical elements with conventional antireflection coating without a combination of non-porous and porous partial-surface system. This has a positive effect on the imaging properties and thus the accuracy of the transfer of the pattern from a mask to an object to be exposed, such as a semiconductor wafer, in particular for optical elements which are used in microlithography.

The part-level system 51 from conventional, ie non-porous layers 54 . 55 is composed of materials which are higher or lower refractive in the wavelength range of the respective optical element, for example in the ultraviolet, visible, near-infrared wavelengths or in the transition region between ultraviolet and visible radiation. The layers 54 . 55 are arranged alternately in order to achieve a destructive interference of the partial beams reflected at the individual layer boundaries, thereby keeping the reflection as low as possible. The at least one porous layer 56 . 56a On the other hand, -c is made of a material which is lower refracting in the respective wavelength range. Lanthanum fluoride, gadolinium fluoride, neodymium fluoride, ytterbium fluoride, aluminum oxide, hafnium oxide, zirconium oxide, niobium oxide, yttrium oxide, scandium oxide, ytterbium oxide, lanthanum oxide and tantalum oxide are particularly suitable as higher refractive materials for the different wavelength ranges. For example, aluminum fluoride, chiolite, cryolite, sodium fluoride, magnesium fluoride, lithium fluoride, silicon dioxide, yttrium fluoride, calcium fluoride and barium fluoride are suitable as lower refracting material in said wavelength ranges.

At the in 5b illustrated embodiment, the multiple porous layers 56a -C, are the porous layers 56a C arranged such that the refractive index in the respective wavelength range at the substrate 50 nearest porous location 56a is highest and at the substrate 50 most remote location 56c is lowest and decreases continuously from location to location. In this case, overall the optical thickness of the second partial system of only porous layers is less than half the wavelength for which the respective optical element is designed, ie for optical elements which are designed for wavelength ranges, the substantially central wavelength. In addition, the refractive indices of the porous layers are preferably smaller than the refractive indices of the non-porous layers. As the material for the one or more layers of the partial porous system, magnesium fluoride and / or silica are preferable. However, other materials such as yttrium fluoride are also conceivable.

It should be pointed out that, in special cases of application, a protective layer can still be applied to the porous layer which is furthest away from the substrate, in order in particular to protect the porous partial-layer system of the antireflection coating from mechanical influences. Material and thickness of this protective layer are selected in particular according to that they do not affect the optical properties of the optical element appreciably negative. Possible materials are for example non-porous silicon dioxide or magnesium fluoride.

Optical elements for a wavelength of 193 nm

The positive influence of porous layers at the interface of an optical element to the surrounding medium will be explained with reference to the following figures. In the 6a These are examples of antireflection coating optical elements optimized for a wavelength of 193 nm, which can be used in microlithography at 193 nm, for example. These are in the 6a Example illustrated an antireflection coating, which is already known. It is based on the doctrine of US Pat. No. 6,825,976 B2 whose contents are fully referenced. On a substrate made of synthetic quartz glass alternating layer of lanthanum fluoride and magnesium fluoride are shown in Table 1, where 1 is the closest to the substrate location and No. 6, the most distant from the substrate location are designated. Table 1 No. material Refractive index at 193 nm Thickness [nm] optical thickness [nm] 1 LaF ₃ 1.68 52.6 88.3 2 MgF ₂ 1:45 7.8 11.4 3 LaF ₃ 1.68 11.0 18.4 4 MgF ₂ 1:45 29.2 42.3 5 LaF ₃ 1.68 25.0 42.0 6 MgF ₂ 1:45 40.8 59.3

The reflection on this optical element according to the prior art is shown for a wavelength of 193 nm over an angle of incidence between 0 ° and 60 ° to the surface normal of the corresponding surface of the optical element, namely for s-polarized radiation (Rs), for p- polarized radiation (Rp) and unpolarized radiation (Ra). At angles of incidence of up to about 10 °, the difference between s-polarized, p-polarized and unpolarized radiation is negligible and the reflection is slightly below 0.4% for all three types of radiation. At angles of incidence from about 10 ° to 15 °, the difference between the reflection for s-polarized radiation, unpolarized radiation and p-polarized radiation increases sharply, in particular, the reflection for s-polarized radiation already at an angle of incidence of 35 ° above a 1% and for unpolarized radiation from an angle of incidence of 45 ° increases above 1%, while the reflection for p-polarized radiation drops to almost zero in the range between 40 ° and 45 ° and only from about 58 ° a reflection of 1% reached.

In contrast, in the 6b -E the reflection at a wavelength of 193 nm for s-polarized radiation, p-polarized radiation and unpolarized radiation over incident angle between 0 ° to 60 ° plotted for optical elements, as proposed here, following a partial layer system of non-porous layers at least one have porous layer at the interface of the optical element to the surrounding medium.

The optical element whose reflection in 6b has an antireflection coating, which is applied according to Table 2 on a synthetic quartz glass substrate having a refractive index of 1.5608 at a wavelength of 193 nm. For example, calcium fluoride having a refractive index of 1.5018 at 193 nm may also be used as the substrate material. Table 2 No. material Refractive index at 193nm Thickness [nm] optical thickness [nm] 1 MgF ₂ 1:45 9.0 13.1 2 LaF ₃ 1.68 10.0 16.8 3 MgF ₂ 1:45 56.2 81.5 4 LaF ₃ 1.68 6.5 10.9 5 MgF ₂ 1:45 29.0 42.0 6 LaF ₃ 1.68 14.2 23.9 7 MgF ₂ + 50% pores 1.22 52.5 63.9

On a partial layer system of nonporous layers of the materials magnesium fluoride and lanthanum fluoride as in the comparative example, a porous medium to the surrounding medium of porous magnesium fluoride is applied, which has a void content of 50 vol .-%. The porous magnesium fluoride layer is preferably applied by means of one of the methods described above. Compared with the reflection of the optical element known from the prior art (see 6a ) has the optical element according to Table 2 (see 6b ) a much lower reflection, namely from well below 0.2% at angles of incidence to 50 °. In addition, the splitting of the reflection, depending on the polarization state of the radiation is significantly lower than in the optical element according to the prior art.

This effect can also be observed for the other optical elements with an additional porous layer which, according to Table 3 (FIG. 6c ), Table 4 ( 6d ) or Table 5 ( 6e ) have an antireflection coating on a substrate made of synthetic quartz glass in the present example and their reflection depending on the angle of incidence in each of the 6c . 6d respectively. 6e are shown. Table 3 No. material Refractive index at 193nm Thickness [nm] optical thickness [nm] 1 MgF ₂ 1:45 9.0 13.1 2 LaF ₃ 1.68 10.0 16.8 3 MgF ₂ 1:45 56.2 81.5 4 LaF ₃ 1.68 6.5 10.9 5 MgF ₂ 1:45 29.0 42.0 6 LaF ₃ 1.68 14.2 23.9 7 SiO ₂ + 60% pores 1.22 52.5 63.9 Table 4 No. material Refractive index at 193nm Thickness [nm] optical thickness [nm] 1 MgF ₂ 1:45 9.0 13.1 2 LaF ₃ 1.68 11.4 19.1 3 MgF ₂ 1:45 44.3 64.2 4 LaF ₃ 1.68 6.5 10.9 5 MgF ₂ 1:45 33.3 48.3 6 LaF ₃ 1.68 12.0 20.1 7 MgF ₂ 1:45 5.0 7.3 8th MgF ₂ + 20% pores 1:36 5.0 6.8 9 MgF ₂ + 30% pores 1.31 7.0 9.2 10 MgF ₂ + 40% pores 1.26 10.0 12.6 11 MgF ₂ + 50% pores 1.22 33.4 40.7 Table 5 No. material Refractive index at 193nm Thickness [nm] optical thickness [nm] 1 MgF ₂ 1:45 10.0 14.5 2 LaF ₃ 1.68 16.0 26.8 3 MgF ₂ 1:45 37.3 54.1 4 LaF ₃ 1.68 8.1 13.6 5 MgF ₂ 1:45 33.1 48.1 6 LaF ₃ 1.68 10.0 16.8 7 SiO ₂ 1:57 8.0 12.6 8th SiO ₂ + 20% pores 1:45 5.0 7.3 9 SiO ₂ + 30% pores 1:39 6.0 8.4 10 SiO ₂ + 40% pores 1:33 8.0 10.7 11 SiO ₂ + 50% pores 1.27 10.0 12.7 12 SiO ₂ + 60% pores 1.22 30.6 37.3

The optical element with an antireflection coating according to Table 3 has a porous layer of silicon dioxide with a pore content of 60% by volume. The porous silicon dioxide layer is preferably applied by means of one of the methods described above.

The optical element with an antireflection coating according to Table 4 has four porous layers of magnesium fluoride, wherein the porous layer closest to the substrate has the lowest void content, namely 20 vol .-%, and thus the highest refractive index of the porous layers during the layer furthest from the substrate has the highest pore content, namely 50% by volume, and thus the lowest refractive index. Between these two porous layers, the intermediate layers have an increasing pore content or decreasing refractive index at 193 nm.

The 193 nm antireflection coating optical element of Table 5 has a silicon dioxide layer on the underlying alternating magnesium fluoride and lanthanum fluoride layers as the outermost layer of the non-porous layer partial layer system. This is followed by five porous silica layers, with the pore content increasing from 50% by volume to 60% by volume such that the pore content is highest at the position farthest from the substrate.

For all optical elements according to Table 2, Table 3, Table 4 and Table 5, the optical thickness of the second partial system of porous layers is less than half the wavelength 193 nm, for which the respective optical element is designed. In addition, the refractive indices of the layers of the porous part-system are equal to or smaller than the refractive indices of the layers of the partial-layer system of non-porous layers.

Optical elements for a wavelength range from 200 nm to 380 nm

The wavelength range from 200 nm to 380 nm essentially comprises the ultraviolet wavelength range, in particular the ranges of the UV-A, UV-B and UV-C radiation. Over the wavelength range from 200 nm to 400 nm, the reflection on optical elements with different antireflection coatings for unpolarized radiation at angles of incidence of 0 °, 20 °, 40 ° and 50 °, measured to the surface normal, was investigated.

In 7a First, as a comparative example, the reflection of an optical element for the ultraviolet wavelength range from 200 nm to 380 nm, which was prepared by applying to a substrate made of synthetic quartz glass an antireflection coating of non-porous, alternately arranged layers of magnesium fluoride and aluminum oxide, conventional for this wavelength range, according to the table 6 was applied. Synthetic quartz glass has a refractive index of 1.4903 at a wavelength of 290 nm. For example, calcium fluoride having a refractive index of 1.4562 at 290 nm may also be used as the substrate material. Table 6 No. material Refractive index at 290nm Thickness [nm] optical thickness [nm] 1 MgF ₂ 1:39 29.4 41.0 2 Al ₂ O ₃ 1.64 6.0 9.9 3 MgF ₂ 1:39 46.8 65.2 4 Al ₂ O ₃ 1.64 17.8 29.3 5 MgF ₂ 1:39 16.5 23.1 6 Al ₂ O ₃ 1.64 41.1 67.5 7 MgF ₂ 1:39 46.2 64.5

For angles of incidence of 0 ° and 20 °, the reflection in the stated wavelength range is between about 0.5% and about 2.5%. At an angle of incidence of 40 °, the reflection is already above 250% above 1.5% and increases to over 4% to the long-wave end of the wavelength range. For an incidence angle of 50 °, the reflection over the entire wavelength range of 200 nm to 400 nm is more than 1.5% and already exceeds 4% from 350 nm.

In contrast, in the 7b -E applied the reflection for optical elements, which as proposed here, following a partial layer system of non-porous layers have at least one porous layer at the interface of the optical element to the surrounding medium. In 7b the reflection of unpolarized radiation of an optical element with an antireflection coating according to Table 7 is applied to a substrate made of synthetic quartz glass for angles of incidence of 0 °, 20 °, 40 ° and 50 °, in 7c the reflection of an optical element with an antireflection coating according to Table 8, in 7d the reflection of an optical element with an antireflection coating according to Table 9 and in 7e the reflection of an optical element with an antireflection coating according to Table 10. Table 7 No. material Refractive index at 290nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.64 7.4 12.1 2 MgF ₂ 1:39 16.1 22.5 3 Al ₂ O ₃ 1.64 25.0 41.0 4 MgF ₂ 1:39 7.9 11.0 5 Al ₂ O ₃ 1.64 49.4 81.1 6 MgF ₂ 1:39 21.8 30.4 7 Al ₂ O ₃ 1.64 13.4 22.1 8th MgF ₂ + 50% pores 1.19 60.3 71.8 Table 8 No. material Refractive index at 290nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.64 9.8 16.2 2 MgF ₂ 1:39 7.3 10.2 3 Al ₂ O ₃ 1.64 7.3 12.0 4 MgF ₂ 1:39 8.7 12.1 5 Al ₂ O ₃ 1.64 28.6 47.0 6 MgF ₂ 1:39 20.4 28.5 7 Al ₂ O ₃ 1.64 17.5 28.8 8th SiO ₂ + 50% pores 1.24 56.9 70.4 Table 9 No. material Refractive index at 290nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.64 10.6 17.5 2 MgF ₂ 1:39 18.2 25.4 3 Al ₂ O ₃ 1.64 21.2 34.9 4 MgF ₂ 1:39 29.8 41.6 5 Al ₂ O ₃ 1.64 9.0 14.8 6 MgF ₂ 1:39 5.0 7.0 7 MgF ₂ + 20% pores 1.31 6.0 7.9 8th MgF ₂ + 30% pores 1.27 8.0 10.2 9 MgF ₂ + 40% pores 1.23 12.0 14.8 10 MgF ₂ + 50% pores 1.19 37.5 44.7 Table 10 No. material Refractive index at 290nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.64 11.4 18.7 2 MgF ₂ 1:39 17.6 24.6 3 Al ₂ O ₃ 1.64 22.5 37.0 4 MgF ₂ 1:39 1.27 37.8 5 Al ₂ O ₃ 1.64 7.0 11.5 6 SiO ₂ 1:49 5.0 7.4 7 SiO ₂ + 20% pores 1:39 5.0 6.9 8th SiO ₂ + 30% pores 1:34 6.0 8.0 9 SiO ₂ + 40% pores 1.29 8.0 10.3 10 SiO ₂ + 50% pores 1.24 10.0 12.4 11 SiO ₂ + 60% pores 1.19 39.5 46.8

The optical element according to Table 7 is applied to a partial layer system of nonporous layers of the materials magnesium fluoride and aluminum oxide as in Comparative Example, a final position towards the surrounding medium of porous magnesium fluoride having a void content of 50 vol .-%. The porous magnesium fluoride layer is preferably applied by means of one of the methods described above. Compared with the reflection of the optical element known from the prior art (see 7a ) has the optical element according to Table 7 (see 7b ) a much lower reflection, namely of well below 0.2% at angles of incidence of 0 ° and 20 ° over the entire wavelength range of 200 nm to 380 nm. Even for higher angles of incidence of 40 ° or 50 °, the reflection remains over the entire Wavelength range well below 1% for 40 ° and 2% for 50 °.

This effect, that the reflection over the entire wavelength range from 200 nm to 400 nm is clearly smaller also for large angles of incidence than in 7a Comparative example shown can also be observed for the other optical elements with additional porous layer, which according to Table 8 ( 7c ), Table 9 ( 7d ) or Table 10 ( 7e ) have an antireflection coating on a substrate of synthetic quartz glass in the present example.

The optical element with an antireflection coating according to Table 8 has a porous layer of silicon dioxide with a pore content of 50% by volume. The porous silicon dioxide layer is preferably applied by means of one of the methods described above. The optical element with an antireflection coating according to Table 9 has four porous layers of magnesium fluoride, wherein the porous layer closest to the substrate has the lowest void content, namely 20 vol.%, And thus also the highest refractive index of the porous layers the layer furthest from the substrate has the highest pore content, namely 50% by volume, and thus the lowest refractive index. Between these two porous layers, the intervening layers have increasing pore content or decreasing refractive index at the central wavelength of 290 nm. The optical element according to Table 10 has a silicon dioxide layer on the underlying alternating magnesium fluoride and aluminum oxide layers as the substrate of the non-porous layers located farthest from the substrate. This is followed by five porous silica layers, the pore content increasing from 20% by volume to 60% by volume at the porous silicon dioxide layer farthest from the substrate.

For all optical elements designed according to Table 7, Table 8, Table 9 and Table 10 for a wavelength in the ultraviolet wavelength range, the optical thickness of the second partial system of porous layers is less than half of the central wavelength 290 nm Refractive indices of the layers of the porous partial system equal to or less than the refractive indices of the layers of the partial system of non-porous layers.

Optical elements for a wavelength range from 380 nm to 750 nm

The wavelength range from 380 nm to 750 nm essentially covers the visible wavelength range. Over the wavelength range of 350 nm to 800 nm, the reflection on optical elements with different antireflection coatings for unpolarized radiation was examined at incident angles of 0 °, 20 °, 40 ° and 50 °, measured to the surface normal.

In 8a First, as a comparative example, the reflection of an optical element for the ultraviolet wavelength range from 380 nm to 750 nm, which was prepared by applying to a substrate made of synthetic quartz glass an antireflection coating of non-porous, alternatingly arranged layers of niobium oxide and silicon dioxide, which is conventional for this wavelength range, according to the table 11 was applied. Synthetic quartz glass has a refractive index of 1.4596 at a wavelength of 565 nm. As the substrate material, for example, optical glasses may also be used, such as the optical glass available under the name BK7 from Schott AG, which has a refractive index of 1.5187 at a wavelength of 546 nm. Table 11 No. material Refractive index at 565nm Thickness [nm] optical thickness [nm] 1 Nb ₂ O ₅ 2.31 8.0 18.5 2 SiO ₂ 1:44 65.3 93.8 3 Nb ₂ O ₅ 2.31 12.7 29.3 4 SiO ₂ 1:44 84.7 121.8 5 Nb ₂ O ₅ 2.31 8.0 18.5 6 SiO ₂ 1:44 84.7 121.7 7 Nb ₂ O ₅ 2.31 20.1 46.6 8th SiO ₂ 1:44 27.4 39.3 9 Nb ₂ O ₅ 2.31 77.0 178.1 10 SiO ₂ 1:44 13.1 18.9 11 Nb ₂ O ₅ 2.31 24.7 57.1 12 MgF ₂ 1:37 95.8 131.6

For angles of incidence of 0 ° and 20 °, the reflection in the wavelength range from 380 nm to 750 nm substantially varies between below about 0.1% and below about 0.4%. For angles of incidence of 40 °, the reflection in the wavelength range from 380 nm to 750 nm varies substantially between approximately 0.3% and slightly above approximately 1.0%. For angles of incidence of 50 °, the reflection over the entire wavelength range from 380 nm to 750 nm is substantially more than 1%.

In contrast, in the 8b -E applied the reflection for optical elements, which as proposed here, following a partial layer system of non-porous layers have at least one porous layer at the interface of the optical element to the surrounding medium. In 8b the reflection of unpolarized radiation of an optical element with an antireflection coating according to Table 12 is applied to a substrate made of synthetic quartz glass for angles of incidence of 0 °, 20 °, 40 ° and 50 °, in FIG 8c the reflection of an optical element with an antireflection coating according to Table 13, in 8d the reflection of an optical element with an antireflection coating according to Table 14 and in 8e the reflection of an optical element with an antireflection coating according to Table 15. Table 12 No. material Refractive index at 565nm Thickness [nm] optical thickness [nm] 1 Nb ₂ O ₅ 2.31 3.5 8.1 2 SiO ₂ 1:44 63.2 90.9 3 Nb ₂ O ₅ 2.31 10.5 24.2 4 SiO ₂ 1:44 49.5 71.2 5 Nb ₂ O ₅ 2.31 3.4 7.9 6 SiO ₂ 1:44 13.0 18.7 7 Nb ₂ O ₅ 2.31 9.5 22.1 8th SiO ₂ 1:44 82.8 119.1 9 Nb ₂ O ₅ 2.31 5.4 12.4 10 MgF ₂ + 50% pores 1.18 124.6 147.3 Table 13 No. material Refractive index at 565nm Thickness [nm] optical thickness [nm] 1 Nb ₂ O ₅ 2.31 5.2 12.0 2 SiO ₂ 1:44 56.7 81.6 3 Nb ₂ O ₅ 2.31 13.6 31.5 4 SiO ₂ 1:44 25.5 36.6 5 Nb ₂ O ₅ 2.31 6.1 14.1 6 SiO ₂ 1:44 28.5 41.0 7 Nb ₂ O ₅ 2.31 18.5 42.9 8th SiO ₂ 1:44 60.3 86.6 9 Nb ₂ O ₅ 2.31 10.4 24.1 10 SiO ₂ + 50% pores 1.22 120.2 146.8 Table 14 No. material Refractive index at 565nm Thickness [nm] optical thickness [nm] 1 Nb ₂ O ₅ 2.31 3.9 9.1 2 SiO ₂ 1:44 62.4 89.7 3 Nb ₂ O ₅ 2.31 11.9 27.5 4 SiO ₂ 1:44 47.4 68.2 5 Nb ₂ O ₅ 2.31 3.1 7.1 6 SiO ₂ 1:44 10.8 15.6 7 Nb ₂ O ₅ 2.31 12.2 28.2 8th SiO ₂ 1:44 70.6 101.5 9 Nb ₂ O ₅ 2.31 5.9 13.6 10 MgF ₂ 1:37 10.0 13.7 11 MgF ₂ + 20% pores 1.30 12.0 15.6 12 MgF ₂ + 30% pores 1.26 16.0 20.1 13 MgF ₂ + 40% pores 1.22 24.0 29.3 14 MgF ₂ + 50% pores 1.18 73.3 86.7 Table 15 No. material Refractive index at 565nm Thickness [nm] optical thickness [nm] 1 Nb ₂ O ₅ 2.31 4.6 10.6 2 SiO ₂ 1:44 60.6 87.1 3 Nb ₂ O ₅ 2.31 13.4 30.9 4 SiO ₂ 1:44 41.8 60.1 5 Nb ₂ O ₅ 2.31 3.0 6.9 6 SiO ₂ 1:44 13.4 19.2 7 Nb ₂ O ₅ 2.31 14.4 33.2 8th SiO ₂ 1:44 65.0 93.4 9 Nb ₂ O ₅ 2.31 5.8 13.4 10 SiO ₂ 1:44 8.0 11.5 11 SiO ₂ + 20% pores 1:36 10.0 13.6 12 SiO ₂ + 30% pores 1:32 12.0 15.8 13 SiO ₂ + 40% pores 1.27 16.0 20.3 14 SiO ₂ + 50% pores 1.22 20.0 24.4 15 SiO ₂ + 60% pores 1.18 74.4 87.4

In the optical element according to Table 12, a layer of porous magnesium fluoride, which has a pore content of 50% by volume, is applied to a partial layer system of nonporous layers of the materials niobium oxide and silicon dioxide as in the comparative example. The porous magnesium fluoride layer is preferably applied by means of one of the methods described above. Compared with the reflection of the optical element known from the prior art (see 8a ) has the optical element according to Table 12 (see 8b ) a much lower reflection, namely of well below 0.2% at angles of incidence of 0 ° and 20 ° over the entire wavelength range of 380 nm to 750 nm. Even for higher angles of incidence of 40 ° or 50 °, the reflection remains over the entire Wavelength range well below 1% for 40 ° and 2% for 50 °.

This effect, that the reflection over the entire wavelength range from 380 nm to 750 nm is clearly smaller also for large angles of incidence than in 8a Comparative example shown, can also be observed for the other optical elements with additional porous layer, which according to Table 13 ( 8c ), Table 14 ( 8d ) or Table 15 ( 8e ) have an antireflection coating on a substrate of synthetic quartz glass in the present example.

The optical element with an antireflection coating according to Table 13 has a porous layer of silicon dioxide with a pore content of 50% by volume. The porous silicon dioxide layer is preferably applied by means of one of the methods described above. The optical element with an antireflection coating according to Table 14 has four porous layers of magnesium fluoride on a porous non-porous part of the non-porous magnesium fluoride layer, wherein the porous layer closest to the substrate, the lowest void content, namely 20 vol .-%, and thus the highest Refractive index of the porous layers, while the most distant from the substrate layer has the highest pore content, namely 50 vol .-%, and thus the lowest refractive index. Between these two porous layers, the intervening layers have increasing pore content or decreasing refractive index at the center wavelength of 565 nm. The optical element according to Table 15 has a silicon dioxide layer on the alternating niobium oxide and silicon dioxide layers as the layer of non-porous layers which is furthest from the substrate of the partial layer system. This is followed by five porous silica layers, with the void content increasing from 20% by volume to 60% by volume at the porous silicon dioxide layer farthest from the substrate.

For all optical elements designed according to Table 12, Table 13, Table 14 and Table 15 for the visible wavelength range, the optical thickness of the second partial system of porous layers is less than half of the mean wavelength 565 nm. In addition, the refractive indices the layers of the porous part-system less than the refractive indices of the layers of the part-system of non-porous layers.

In 8f For example, the reflectance for a further variant of an optical element for the visible wavelength range is shown with an antireflection coating which has a porous magnesium fluoride layer with 50% by volume pores on a non-porous part-layer system (see Table 16). The essential difference from the embodiments described above according to Tables 12 to 15 is the materials of the non-porous part-system. Instead of alternating layers of niobium oxide and silicon dioxide, there are alternately arranged layers of silicon dioxide and aluminum oxide, wherein a silicon dioxide layer further away from the substrate has been replaced by a layer of niobium oxide. Thus, in the anti-reflection coating shown in Table 16, there is only one layer whose refractive index at 565 nm is greater than 1.25 times the refractive index of the synthetic quartz glass substrate at 565 nm at 1.4596. Nevertheless, the reflection path over the visible wavelength range for the different angles of incidence is comparable to the reflection curve for the other variants (see 8b -e). This example has the particular advantage that, apart from one layer, only materials with very low absorption are used and thus a particularly high transmission can be obtained. Table 16 No. material Refractive index at 565nm Thickness [nm] optical thickness [nm] 1 SiO ₂ 1:44 63.0 90.5 2 Al ₂ O ₃ 1.63 14.5 23.5 3 SiO ₂ 1:44 57.3 82.4 4 Al ₂ O ₃ 1.63 46.2 75.1 5 SiO ₂ 1:44 14.8 21.3 6 Al ₂ O ₃ 1.63 106.3 172.9 7 SiO ₂ 1:44 33.7 48.5 8th Al ₂ O ₃ 1.63 17.8 29.0 9 SiO ₂ 1:44 131.1 188.5 10 Al ₂ O ₃ 1.63 99.6 162.0 11 Nb ₂ O ₅ 2.31 8.5 19.7 12 Al ₂ O ₃ 1.63 36.3 59.0 13 SiO ₂ 1:44 22.6 32.6 14 Al ₂ O ₃ 1.63 40.9 66.6 15 MgF ₂ + 50% pores 1.18 115.8 137.0

Optical elements for a wavelength range from 750 nm to 1400 nm

The wavelength range from 750 nm to 1400 nm essentially encompasses the near-infrared wavelength range. Over the wavelength range of 700 nm to 1500 nm, the reflection on optical elements with different antireflection coatings for unpolarized radiation was examined at incident angles of 0 °, 20 °, 40 ° and 50 °, measured to the surface normal.

In 9a First, as a comparative example, the reflection of an optical element for the ultraviolet wavelength range from 750 nm to 1400 nm, which has been prepared by applying to a substrate made of synthetic quartz glass an antireflection coating of non-porous, alternating layers of tantalum oxide and silicon dioxide, conventional for this wavelength range, according to the table 17 was applied. Synthetic quartz glass has a refractive index of 1.4492 at a wavelength of 1100 nm. As the substrate material, for example, optical glasses may also be used, such as the optical glass available under the name LF5 from Schott AG, which has a refractive index of 1.5659 at a wavelength of 1060 nm. Table 17 No. material Refractive index at 1100nm Thickness [nm] optical thickness [nm] 1 Ta ₂ O ₅ 2:01 10.0 20.1 2 SiO ₂ 1:45 64.0 92.7 3 Ta ₂ O ₅ 2:01 20.1 40.4 4 SiO ₂ 1:45 43.4 62.9 5 Ta ₂ O ₅ 2:01 40.6 81.4 6 SiO ₂ 1:45 13.3 19.2 7 Ta ₂ O ₅ 2:01 89.1 178.7 8th SiO ₂ 1:45 10.0 14.5 9 Ta ₂ O ₅ 2:01 70.8 142.1 10 SiO ₂ 1:45 26.9 39.0 11 Ta ₂ O ₅ 2:01 23.9 48.1 12 MgF ₂ 1:37 161.1 221.2

For angles of incidence of 0 ° and 20 °, the reflection in the wavelength range of 750 nm to 1400 nm substantially varies between about 0.2% and about 0.5%. For angles of incidence of 40 °, the reflection in the wavelength range from 750 nm to 1400 nm varies over wide ranges between about 0.6% and about 1.0%. For angles of incidence of 50 °, the reflection over the entire wavelength range from 750 nm to 1400 nm over wide ranges is above 1.5%.

In contrast, in the 9b -E applied the reflection for optical elements, which as proposed here, following a partial layer system of non-porous layers have at least one porous layer at the interface of the optical element to the surrounding medium. In 9b the reflection of unpolarized radiation of an optical element with an antireflection coating according to Table 18 is applied to a substrate made of synthetic quartz glass for angles of incidence of 0 °, 20 °, 40 ° and 50 °, in 9c the reflection of an optical element with an antireflection coating according to Table 19, in 9d the reflection of an optical element with an antireflection coating according to Table 20 and in 9e the reflection of an optical element with an antireflection coating according to Table 21. Table 18 No. material Refractive index at 1100nm Thickness [nm] optical thickness [nm] 1 SiO ₂ 1:45 20.0 29.0 2 Ta ₂ O ₅ 2:01 10.0 20.1 3 SiO ₂ 1:45 62.0 89.9 4 Ta ₂ O ₅ 2:01 19.9 40.0 5 SiO ₂ 1:45 37.9 54.9 6 Ta ₂ O ₅ 2:01 35.1 70.3 7 SiO ₂ 1:45 21.1 30.5 8th Ta ₂ O ₅ 2:01 67.3 135.0 9 SiO ₂ 1:45 10.0 14.5 10 Ta ₂ O ₅ 2:01 70.7 141.9 11 SiO ₂ 1:45 29.4 42.6 12 Ta ₂ O ₅ 2:01 32.7 65.6 13 SiO ₂ 1:45 84.9 123.0 14 Ta ₂ O ₅ 2:01 10.0 20.1 15 MgF ₂ + 50% pores 1.18 182.0 215.1 Table 19 No. material Refractive index at 1100nm Thickness [nm] optical thickness [nm] 1 SiO ₂ 1:45 10.0 14.5 2 Ta ₂ O ₅ 2:01 10.0 20.1 3 SiO ₂ 1:45 59.6 86.3 4 Ta ₂ O ₅ 2:01 16.4 32.9 5 SiO ₂ 1:45 32.2 46.7 6 Ta ₂ O ₅ 2:01 26.9 54.0 7 SiO ₂ 1:45 25.2 36.6 8th Ta ₂ O ₅ 2:01 62.0 124.4 9 SiO ₂ 1:45 10.0 14.5 10 Ta ₂ O ₅ 2:01 79.0 158.6 11 SiO ₂ 1:45 25.4 36.8 12 Ta ₂ O ₅ 2:01 39.4 79.0 13 SiO ₂ 1:45 69.2 100.2 14 Ta ₂ O ₅ 2:01 13.2 26.5 15 SiO ₂ + 50% pores 1.22 176.1 214.8 Table 20 No. material Refractive index at 1100nm Thickness [nm] optical thickness [nm] 1 SiO ₂ 1:45 20.0 29.0 2 Ta ₂ O ₅ 2:01 10.0 20.1 3 SiO ₂ 1:45 63.0 91.3 4 Ta ₂ O ₅ 2:01 20.0 40.2 5 SiO ₂ 1:45 36.7 53.2 6 Ta ₂ O ₅ 2:01 32.3 64.8 7 SiO ₂ 1:45 21.3 30.8 8th Ta ₂ O ₅ 2:01 62.6 125.5 9 SiO ₂ 1:45 10.0 14.5 10 Ta ₂ O ₅ 2:01 72.4 145.3 11 SiO ₂ 1:45 27.3 39.5 12 Ta ₂ O ₅ 2:01 35.1 70.5 13 SiO ₂ 1:45 69.4 100.5 14 Ta ₂ O ₅ 2:01 10.0 20.1 15 MgF ₂ 1:37 12.0 16.5 16 MgF ₂ + 20% pores 1.30 16.0 20.7 17 MgF ₂ + 30% pores 1.26 24.0 30.2 18 MgF ₂ + 40% pores 1.22 40.0 48.8 19 MgF ₂ + 50% pores 1.18 107.8 127.3 Table 21 No. material Refractive index at 1100nm Thickness [nm] optical thickness [nm] 1 SiO ₂ 1:45 20.0 29.0 2 Ta ₂ O ₅ 2:01 10.0 20.1 3 SiO2 1:45 63.3 91.7 4 Ta ₂ O ₅ 2:01 20.0 40.2 5 SiO ₂ 1:45 36.1 52.3 6 Ta ₂ O ₅ 2:01 31.3 62.8 7 SiO ₂ 1:45 21.3 30.8 8th Ta ₂ O ₅ 2:01 60.1 120.6 9 SiO ₂ 1:45 10.0 14.5 10 Ta ₂ O ₅ 2:01 74.3 149.1 11 SiO ₂ 1:45 25.9 37.5 12 Ta ₂ O ₅ 2:01 35.7 71.7 13 SiO ₂ 1:45 62.1 90.0 14 Ta ₂ O ₅ 2:01 10.0 20.1 15 SiO ₂ 1:45 10.0 14.5 16 SiO ₂ + 20% pores 1:36 14.0 19.0 17 SiO ₂ + 30% pores 1.31 25.6 33.7 18 SiO ₂ + 40% pores 1.27 20.0 25.3 19 SiO ₂ + 50% pores 1.22 36.0 43.9 20 SiO ₂ + 60% pores 1.17 108.5 127.4

In the optical element according to Table 18, a layer of porous magnesium fluoride, which has a pore content of 50% by volume, is applied to a partial layer system of non-porous layers of the materials tantalum oxide and silicon dioxide as in the comparative example. The porous magnesium fluoride layer is preferably applied by means of one of the methods described above. Compared with the reflection of the optical element known from the prior art (see 9a ) has the optical element according to Table 18 (see 9b ), a much lower reflection, namely of well below 0.2% at angles of incidence of 0 ° and 20 ° over the entire wavelength range of 750 nm to 1400 nm. Even for higher angles of incidence of 40 ° or 50 °, the reflection remains over this wavelength range well below 1% for 40 ° and 2% for 50 °.

This effect, that the reflection over the entire wavelength range from 750 nm to 1400 nm is clearly smaller also for large angles of incidence than in 9a Comparative example shown, can also be observed for the other optical elements with additional porous layer, which according to Table 19 ( 9c ), Table 20 ( 9d ) or Table 21 ( 9e ) have an antireflection coating on a substrate of synthetic quartz glass in the present example.

The optical element with an antireflection coating according to Table 19 has a porous layer of silicon dioxide with a void content of 50% by volume. The porous silicon dioxide layer is preferably applied by means of one of the methods described above. The optical element with an antireflection coating according to Table 20 has four porous layers of magnesium fluoride on a nonporous magnesium fluoride layer which terminates the non-porous part-layer system The closest porous layer has the lowest void content, namely 20 vol.%, and thus also the highest refractive index of the porous layers, while the layer furthest from the substrate has the highest void content, namely 50 vol.%, and thus the having the lowest refractive index. Between these two porous layers, the intervening layers have increasing pore content or decreasing refractive index at the central wavelength of 1100 nm. The optical element shown in Table 21 has a silicon dioxide layer on the alternating tantalum oxide and silicon dioxide layers as the substrate of the non-porous layers that is farthest from the substrate. This is followed by five porous silica layers, the pore content increasing from 20% by volume to 60% by volume at the porous silicon dioxide layer farthest from the substrate.

For all optical elements designed according to Table 18, Table 19, Table 20 and Table 21 for a wavelength in the near infrared wavelength range, the optical thickness of the second partial system of porous layers is less than half of the central wavelength 1100 nm Refractive indices of the layers of the porous partial system less than the refractive indices of the layers of the partial system of non-porous layers.

Optical elements for a wavelength range from 250 nm to 500 nm The wavelength range from 250 nm to 500 nm essentially covers the ultraviolet and visible wavelength ranges, the spectral ranges UV-C and VIS being partially covered and the spectral ranges UV-A and UV-B being completely covered , Over the wavelength range from 240 nm to 550 nm, the reflection on optical elements with different antireflection coatings for unpolarized radiation was examined at incident angles of 0 °, 20 °, 40 ° and 50 °, measured to the surface normal.

In 10a is first shown as a comparative example, the reflection of an optical element for the UV to VIS wavelength range of 250 nm to 500 nm, which was prepared by applying to a synthetic substrate of a conventional anti-reflective coating for this wavelength range of non-porous, alternately arranged layers of scandium and Silicon dioxide was applied according to Table 22. Synthetic quartz glass has a refractive index of 1.4729 at a wavelength of 375 nm. Calcium fluoride, for example, which has a refractive index of 1.4440 at 375 nm can also be used as the substrate material. Table 22 No. material Refractive index at 375nm Thickness [nm] optical thickness [nm] 1 Sc ₂ O ₃ 2:03 9.0 18.3 2 SiO ₂ 1:45 34.2 49.7 3 Sc ₂ O ₃ 2:03 16.5 33.6 4 SiO ₂ 1:45 38.5 55.8 5 Sc ₂ O ₃ 2:03 9.0 18.3 6 SiO ₂ 1:45 74.1 107.4 7 Sc ₂ O ₃ 2:03 10.3 21.0 8th SiO ₂ 1:45 26.4 38.2 9 Sc ₂ O ₃ 2:03 41.4 84.0 10 SiO ₂ 1:45 9.0 13.1 11 Sc ₂ O ₃ 2:03 26.2 53.2 12 MgF ₂ 1:38 62.3 86.1

For angles of incidence of 0 ° and 20 °, the reflection in the wavelength range from 250 nm to 500 nm substantially varies between below about 0.2% and about 0.6%. For incidence angles of 40 °, the reflection in the wavelength range from 250 nm to 500 nm varies over wide ranges between about 0.4% and about 1.2%. For angles of incidence of 50 °, the reflection over the entire wavelength range from 250 nm to 500 nm varies over wide ranges between approximately 1% and approximately 2%.

In contrast, in the 10b -E applied the reflection for optical elements, which as proposed here, following a partial layer system of non-porous layers have at least one porous layer at the interface of the optical element to the surrounding medium. In 10b the reflection of unpolarized radiation of an optical element with an antireflection coating according to Table 23 is applied to a substrate made of synthetic quartz glass for angles of incidence of 0 °, 20 °, 40 ° and 50 °, in 10c the reflection of an optical element with an antireflection coating according to Table 24, in 10d the reflection of an optical element with an antireflection coating according to Table 25 and in 10e the reflection of an optical element with an antireflection coating according to Table 26. Table 23 No. material Refractive index at 375nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.63 51.8 84.2 2 Sc ₂ O ₃ 2:03 19.4 39.3 3 Al ₂ O ₃ 1.63 12.9 21.0 4 Sc ₂ O ₃ 2:03 30.0 60.9 5 Al ₂ O ₃ 1.63 55.2 89.8 6 MgF ₂ + 50% pores 1.19 74.9 88.9 Table 24 No. material Refractive index at 375nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.63 51.8 84.2 2 Sc ₂ O ₃ 2:03 19.4 39.3 3 Al ₂ O ₃ 1.63 12.9 21.0 4 Sc ₂ O ₃ 2:03 30.0 60.9 5 Al ₂ O ₃ 1.63 55.2 89.8 6 SiO ₂ + 60% pores 1.18 74.0 87.3 Table 25 No. material Refractive index at 375nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.63 54.4 88.5 2 Sc ₂ O ₃ 2:03 17.0 34.5 3 Al ₂ O ₃ 1.63 17.8 29.0 4 Sc ₂ O ₃ 2:03 23.2 47.1 5 Al ₂ O ₃ 1.63 53.5 87.1 6 MgF ₂ 1:38 6.0 8.3 7 MgF ₂ + 20% pores 1.30 7.0 9.1 8th MgF ₂ + 30% pores 1.26 9.0 11.4 9 MgF ₂ + 40% pores 1.23 14.0 17.2 10 MgF ₂ + 50% pores 1.19 45.7 54.2 Table 26 No. material Refractive index at 375nm Thickness [nm] optical thickness [nm] 1 Al ₂ O ₃ 1.63 54.6 88.8 2 Sc ₂ O ₃ 2:03 16.9 34.3 3 Al ₂ O ₃ 1.63 18.2 29.5 4 Sc ₂ O ₃ 2:03 22.6 46.0 5 Al ₂ O ₃ 1.63 50.7 82.6 6 SiO ₂ 1:47 5.0 7.4 7 SiO ₂ + 20% pores 1:37 5.0 6.9 8th SiO ₂ + 30% pores 1:32 7.0 9.3 9 SiO ₂ + 40% pores 1.28 8.0 10.2 10 SiO ₂ + 50% pores 1.23 12.0 14.7 11 SiO ₂ + 60% pores 1.18 48.9 57.7

In the case of the optical element according to Table 23, a layer of porous magnesium fluoride, which has a pore content of 50% by volume, is applied to a partial layer system of non-porous layers of the materials scandium oxide and aluminum oxide. The porous magnesium fluoride layer is preferably applied by means of one of the methods described above. Compared with the reflection of the optical element known from the prior art (see 10a ) has the optical element according to Table 23 (see 10b ) has a much lower reflection, namely of well below 0.2% at angles of incidence of 0 ° and 20 ° over the entire wavelength range of 250 nm to 500 nm. Even for higher angles of incidence of 40 ° or 50 °, the reflection remains over this wavelength range mostly well below 1% for 40 ° and below 2% for 50 °.

This effect, that the reflection over the entire wavelength range from 250 nm to 500 nm is clearly smaller also for large angles of incidence than in 10a Comparative example shown can also be observed for the other optical elements with additional porous layer, which according to Table 24 ( 10c ), Table 25 ( 10d ) or Table 26 ( 10e ) have an antireflection coating on a substrate of synthetic quartz glass in the present example.

The optical element with an antireflection coating according to Table 24 has a porous layer of silicon dioxide with a pore content of 60% by volume. The porous silicon dioxide layer is preferably applied by means of one of the methods described above. The optical element with an antireflection coating according to Table 25 has four porous layers of magnesium fluoride on a porous non-porous part of the non-porous magnesium fluoride layer, wherein the porous layer closest to the substrate, the lowest void content, namely 20 vol .-%, and thus the has the highest refractive index of the porous layers, while the most distant from the substrate layer has the highest pore content, namely 50 vol .-%, and thus the lowest refractive index. Between these two porous layers, the intervening layers have increasing pore content or decreasing refractive index at the central wavelength of 375 nm. The optical element according to Table 26 has as the substrate from the substrate furthest away position of the non-porous layers of partial layer system on a Siliziumdioxidlage on the alternating scandium oxide and alumina layers. This is followed by five porous silica layers, the pore content increasing from 20% by volume to 60% by volume at the porous silicon dioxide layer farthest from the substrate.

For all optical elements designed to have a wavelength in the ultraviolet to visible wavelength range according to Table 23, Table 24, Table 25, and Table 26, the optical thickness of the second partial system of porous layers is less than half the mean wavelength of 375 nm For example, the refractive indices of the layers of the porous part-system are smaller than the refractive indices of the layers of the part-system of non-porous layers. All embodiments according to Table 23, Table 24, Table 25 and Table 26 have a total thickness of less than 250 nm, well below the total layer thickness of 360 nm of the conventional antireflection coating according to Table 22. In addition, in all embodiments according to Tables 23 to 26, the proportion of scandium oxide layers is only half as large as in the comparative example according to Table 22. This has the advantage of allowing antireflection coatings with significantly reduced absorption.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• WO 2008/148462 A1 [0003]
• US 6825976 B2 [0045]

Claims (13)

A method for producing an optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating having at least one layer of porous material, wherein the porous layer is applied by applying two inorganic materials together and then one of the materials is removed, so that form pores in the material not removed. A method according to claim 1, characterized in that as antireflection coating at least two layers are applied to a substrate and the substrate from the substrate furthest removed layer is applied as a porous layer, wherein as a material not to be removed, a low-refractive material in the wavelength range of the optical element is applied. A method according to claim 1 or 2, characterized in that the two inorganic materials are applied simultaneously or as alternating thin layers. Method according to one of claims 1 to 3, characterized in that the material to be removed is removed chemically or chemically-physically. Optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range with an antireflection coating comprising at least one layer of porous material, produced by the method according to one of claims 1 to 4. An optical element according to claim 5, wherein the antireflection coating comprises a first part-layer system of non-porous layers of materials higher and lower alternating in the wavelength range of the optical element on one substrate and a second part-system of one or more porous layers farther from the substrate, wherein the at least one porous layer is based on a lower refractive material in the wavelength range of the optical element. Optical element for a wavelength range in the ultraviolet, visible and / or near-infrared wavelength range, the antireflection coating comprises a first part-layer system of non-porous layers of alternately in the wavelength range of the optical element higher and lower refractive materials on a substrate and a second, further away from the substrate part-system from a or more porous layers, wherein the at least one porous layer is based on a lower refractive material in the wavelength range of the optical element. An optical element according to claim 6 or 7, characterized in that the second layer system comprises two or more porous layers, wherein the refractive index of the porous layers closest to the substrate is at the highest of all porous layers and the refractive index of each further porous layer is continuously lower. Optical element according to one of claims 6 to 8, characterized in that the optical thickness of the second part-system is less than half the wavelength for which the optical element is designed. Optical element according to one of claims 6 to 9, characterized in that the refractive indices of the layers of the second part-system are smaller than the refractive indices of the layers of the first part-system. Optical element according to one of claims 6 to 10, characterized in that the first part-system does not have more than one layer whose refractive index in the wavelength range of the optical element is greater than 1.25 times the corresponding refractive index of the substrate. Optical element according to one of claims 6 to 11, characterized in that the first part-layer system as a higher refractive material of one or more of the group lanthanum fluoride, gadolinium fluoride, neodymium fluoride, ytterbium fluoride, alumina, hafnium oxide, zirconium oxide, niobium oxide, yttrium oxide, scandium oxide, ytterbium oxide, tantalum oxide and as the lower refractive material, one or more of the group comprises aluminum fluoride, chiolite, cryolite, sodium fluoride, magnesium fluoride, lithium fluoride, silica, yttrium fluoride, calcium fluoride, barium fluoride. Optical element according to one of claims 5 to 12, characterized in that it comprises magnesium fluoride and / or silicon dioxide as the material of the one or more porous layers.

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