Optical elements for the ultraviolet wavelength range

Abstract

To increase transmittance or reflectance, we propose an optical element for the ultraviolet (UV) wavelength range, which comprises a substrate and an optical coating configured as a dielectric layer system, the dielectric layer system comprising at least two different substrate layers (56, 57) having different refractive indices at certain wavelengths within the UV wavelength range and arranged alternately, and the optical element comprising a nanolayer system (71, 72) at the position of at least one of the substrate layers (57) having a higher refractive index.

Description

Technical Field

[0001] The present invention relates to an optical element for the ultraviolet (UV) wavelength range. This optical element comprises a substrate and an optical coating configured as a dielectric layer system. The dielectric layer system comprises layers of at least two different substrates having different refractive indices at a certain wavelength within the UV wavelength range, and the layers of different substrates are arranged alternately. The present invention further relates to an optical system having such an optical element. This application claims priority from German Patent Application No. 102023204746.2 filed on May 22, 2023, the entire content of which is incorporated herein by reference.

Background Art

[0002] Optical elements for the UV wavelength range must meet high demands, especially for applications within the short-wavelength UV wavelength range, for example in the range of approximately 100 nm to 300 nm. In this context, the reflectance or transmittance should be as good as possible, depending on whether the optical element is a reflective optical element or a transmissive optical element. Furthermore, the lifespan should also be within the range of several years as much as possible. Optical elements for the UV wavelength range usually comprise a substrate and an optical coating configured as a dielectric layer system. This dielectric layer system comprises layers of at least two different substrates having different refractive indices at a certain wavelength within the UV wavelength range, in order to improve the transmittance or reflectance of the optical element. This optical coating can also contribute to increasing the lifespan to a certain extent. In particular, for use in reflection, the optical coating can additionally comprise a metal layer on the substrate side.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The object of the present invention is to propose an optical element especially for the short-wavelength UV wavelength range.

Means for Solving the Problems

[0004] This objective is achieved by an optical element for the UV wavelength range, which comprises a substrate and an optical coating configured as a dielectric layer system, the dielectric layer system comprising at least two different substrate layers having different refractive indices at certain wavelengths within the UV wavelength range, the layers of different substrates being arranged alternately, and the optical element comprising a nanolayer system at the position of at least one layer of the substrate having a higher refractive index.

[0005] It has been found that both reflectance or transmittance and lifetime can be improved by placing at least one nanolayer system, particularly at the position of a substrate layer with a higher refractive index. In contrast to known dielectric layer systems that increase transmittance or reflectance through interference in the thickness of the optical layer at approximately one-quarter of the incident wavelength, nanolayer systems are structures composed of multiple layers having thicknesses in the nanometer range, and these multiple layers can be used to directly influence the refractive index and absorbance of each nanolayer system. To improve the optical properties of at least partially replaced layers, it is advantageous if at least a portion of the nanolayers is made from one or more materials having a refractive index similar to or higher than that of the replaced material. The lower the absorbance, the greater the transmittance or reflectance of the optical element having a dielectric layer system improved by the nanolayer system. The smaller the radiation absorbed within each dielectric layer system, the smaller the energy that enters the optical system, and this energy would otherwise cause damage to the dielectric system due to expansion of individual layers, resulting in changes in the corresponding optical parameters and stress generation due to the fracture of individual layers.

[0006] It is advantageous to replace at least one layer of a substrate with a higher refractive index with a nanolayer system, at least partially. In certain preferred examples, even one or more layers of a substrate with a higher refractive index can be completely replaced with a nanolayer system to improve the transmittance or reflectance of an optical element, as well as its lifespan.

[0007] In certain preferred examples, the optical element is designed for wavelengths of 190 nm to 300 nm, preferably 190 nm to 200 nm. Within the UV wavelength range, providing a nanolayer system at the position of at least one layer of a substrate with a higher refractive index has a particularly positive effect, firstly, on the transmittance or reflectance of the optical element, and secondly, on its lifetime.

[0008] Preferably, at least one nanolayer system is composed of at least two different nanolayer materials having different refractive indices at some wavelengths within the UV wavelength range, and the different nanolayer materials are arranged alternately so that the refractive index and absorbance of the resulting nanolayer system, and therefore the dielectric layer system of the optical element, can be influenced in the most targeted way possible and without excessive cost / complexity.

[0009] It has been found that nanolayer materials with higher and / or lower refractive indices are particularly advantageous if they are the same as substrates with higher and / or lower refractive indices, respectively. Thus, layers in dielectric layer systems, and also layers in nanolayer systems, can be applied to their respective optical elements in a continuous process without modification or transfer to different coating chambers.

[0010] In particular, for use in optical elements with short-wavelength UV radiation, substrates with a higher refractive index are oxides, especially Al2O3, MgAl2O4, and Lu3Al5O 12 Preferably, the material is one or more of the materials in the group consisting of GeO2, CaO, MgO, HfO2, Si3N4, Y2O3, and La2O3. These materials are suitable for incident radiation wavelengths in the range of 100 nm to 300 nm, preferably 190 nm to 300 nm, and particularly preferably 190 nm to 200 nm.

[0011] For optical elements used particularly with short-wavelength UV radiation, it is equally preferable that the substrate having a lower refractive index be silicon dioxide and / or amorphous fluoropolymer (fluoropolymer). These materials are suitable for incident radiation wavelengths in the range of 100 nm to 300 nm, preferably 190 nm to 300 nm, and particularly preferably 190 nm to 200 nm.

[0012] It is particularly advantageous if each layer of the nanolayer system also contains one or more of these materials, and especially if at least one nanolayer system is composed of at least two different nanolayer materials having different refractive indices at some wavelengths within the UV wavelength range, and the different nanolayer materials are arranged alternately such that the nanolayer materials with higher and / or lower refractive indices are the same as the substrates with higher and / or lower refractive indices, respectively, of the dielectric layer system of the optical element.

[0013] In a particularly preferred example, the optical coating is designed as a reflective coating, which can be embodied as a pure dielectric coating, or it can additionally include a metallic layer as a reflective coating. In the former case in particular, it is advantageous that at least one layer comprising the nanolayer system is located in the optical coating at the third furthest point from the substrate. In this case, it is preferable that the optical element has the nanolayer system at at least one position among the seven layers with higher refractive indices that are arranged furthest from the substrate. In this case, it is advantageous that the optical element has the nanolayer system at all positions of each of the three, four, five, six, or seven layers with higher refractive indices that are arranged furthest from the substrate. It has been found that providing the nanolayer system in a region of the dielectric layer system that is farther from the substrate, i.e., in a region that is closer to or adjacent to the outer periphery of the optical element, can have a particularly significant effect on increasing the reflectivity of the optical element.

[0014] In the case of reflective coatings having or not having a metallic reflective coating on at least one layer with a higher refractive index, the latter is advantageous in replacing the substrate-facing side with a nanolayer system. In many cases where it is not desirable to replace the entire layer with a nanolayer system, if the nanolayer system is placed on the substrate-facing side of the relevant layer of the higher refractive index material, a significant effect of the nanolayer system on the transmittance or reflectance of the optical element, and on the lifespan of the optical element, can be realized. This effect is particularly pronounced in the case of at least one of the three layers with the higher refractive index that are furthest from the substrate, if the substrate-facing side of this layer is replaced with a nanolayer system.

[0015] In an additional preferred example, the optical coating is designed as an anti-reflective coating, and the optical element does not have a nanolayer system at the position of the layer furthest from the substrate. In the preferred example as a transmissive optical element, it is also advantageous to have at least one nanolayer system in the optical coating, but it has been found that the transmittance can be particularly increased by not placing a nanolayer system at the position of the layer furthest from the substrate.

[0016] It has also been demonstrated that, with respect to the transmittance and reflectance of optical elements, and with respect to the lifespan of optical elements, it is advantageous to replace both the substrate-facing and substrate-away-from-substrate sides of at least one layer having a higher refractive index with a nanolayer system. In this case, it is preferable that both nanolayer systems are composed of the same material.

[0017] Overall, it has been proven advantageous to replace at least half of the layers with a nanolayer system in at least one layer having a higher refractive index, particularly if at least one of the layers in question is located third furthest from the substrate, which can significantly affect the transmittance or reflectance of the optical element, as well as its lifespan.

[0018] Upon reflection within the UV wavelength range, a standing wave of the electric field is formed within the optical element, specifically within the dielectric layer system. In a particularly preferred example, the optical element is provided with a nano-layer system at a location where the external electric field strength of the standing wave exists at at least one layer having a higher refractive index. This enables it to particularly effectively influence both the absorptance of the dielectric layer system and thus the transmittance or reflectance and the lifetime of the optical element.

[0019] Furthermore, the above object is achieved by an optical system comprising the described optical element. Such optical systems are particularly well-suited as components of lithographic apparatuses and as components of wafer and / or mask inspection systems, but are also well-suited as components for use with lasers, particularly for use within the UV wavelength range.

[0020] The present invention will be described in more detail with reference to preferred embodiments.

Brief Description of the Drawings

[0021] [Figure 1] It is a basic schematic diagram of a UV lithographic apparatus. [Figure 2] It is a basic schematic diagram of an inspection system. [Figure 3] It is a diagram schematically showing an optical element having a dielectric layer system. [Figure 4] It is a diagram schematically showing a pair of layers having a nano-layer system. [Figure 5] It is a diagram schematically showing a layer pair having two nano-layer systems. [Figure 6] It is a diagram showing the reflectance at the first optical element at 193 nm as a function of the angle of incidence. [Figure 7] It is a diagram showing the configuration of the dielectric layer system of the first optical element. [Figure 8] It is a diagram showing the standing wave formed upon reflection at the first optical element. [Figure 9] It is a diagram showing the reflectance at the second optical element at 193 nm as a function of the angle of incidence. [Figure 10]This figure shows the configuration of the dielectric layer system of the second optical element. [Figure 11] This diagram shows the configuration of the dielectric layer system of the third optical element. [Figure 12] This figure shows the reflectance of the third optical element at 193 nm as a function of the angle of incidence. [Modes for carrying out the invention]

[0022] Figure 1 shows a basic schematic diagram of apparatus 1 for UV lithography, particularly for wavelengths in the range of 190 nm to 300 nm. The UV lithography apparatus 1 comprises, as essential components, two optical systems 12 and 14, namely the illumination system 12 and the projection system 14. Performing lithography requires a radiation source, preferably an excimer laser, which emits light at, for example, 193 nm or 248 nm, and can be an essential part of the UV lithography apparatus. The radiation emitted by the radiation source 10 is regulated using the illumination system 12, thereby illuminating a mask, also called a reticle. In the example shown here, the illumination system 12 comprises transmissive and reflective optical elements. The transmissive optical element 120 focuses the radiation 11, for example, and the reflective optical element 121 deflects the radiation, for example, as shown here in a representative manner. In known ways, the illumination system 12 can combine a wide variety of transmissive, reflective, and other optical elements in arbitrary, and even more complex, manner. It should be noted that the mask 13 can also be embodied as a reflective or transmissive optical element, as proposed here.

[0023] The mask 13 has a structure on its surface, which is transferred to the element to be exposed, for example, a wafer in the context of semiconductor component production, using the projection system 14. In this example, the mask 13 is embodied as a transmissive optical element. In another embodiment, the mask 13 can also be configured as a reflective optical element. The projection system 14 comprises at least one transmissive optical element in the example shown herein. In the example shown herein, two transmissive optical elements 140 and 141 are shown in a representative manner, and they serve, for example, to reduce the structure on the mask 13 to a size desirable for exposure of the wafer 15. The projection system 14 can also be provided with reflective optical elements, and a wide variety of optical elements can be combined with each other in any known way. In particular, it should be noted that in the case of an optical system optimized for wavelengths less than 200 nm, an optical system without transmissive optical elements can also be provided.

[0024] The reflective optical element 121 is a mirror having a reflective surface 1210, which is provided with an optical coating in the form of a dielectric layer system having at least one nanolayer system. In this example, the reflective optical element 121 has a metallic reflective coating below the dielectric layer system. The dielectric layer system not only improves the reflectivity at the emission wavelength of the excimer laser, particularly when using an excimer laser as a radiation source within a specific wavelength range, but also protects the metallic reflective coating from oxidation and other damage. In particular, a metallic layer made of aluminum has been proven to be valuable as a metallic reflective coating for use with good reflectivity over a wide wavelength range, for example, 190 nm to 300 nm. Other suitable metals are precious metals and platinum group metals, particularly for use in glancing incident applications. In relation to the example shown in Figure 1, only one reflective optical element 121 for the UV wavelength range has been described, but it should be noted that two, three, four, five or more reflective optical elements of this type can be provided, for example, in an optical system for UV lithography.

[0025] The UV lithography apparatus 1 shown in Figure 1 also includes transmissive optical elements configured as lenses 120, 140, and 141 in this example. The latter similarly includes an optical coating in the form of a dielectric layer system having at least one nanolayer system on at least its front surface in the beam path. The dielectric layer system functions as an anti-reflective coating and can therefore increase the transmittance of each lens. In particular, optical systems for UV lithography may also include two or more, i.e., three, four, five, six, seven, or more transmissive optical elements.

[0026] Reflective or transmissive optical elements having a dielectric layer system with at least one nanolayer system can also be used in wafer or mask inspection systems and in optical systems for laser applications. One preferred embodiment of wafer inspection system 2 is schematically shown in Figure 2. The description applies similarly to mask inspection systems.

[0027] The wafer inspection system 2 comprises a radiation source 20, the radiation 20 of which is directed onto the wafer 25 by an optical system 22. For this purpose, the radiation is reflected onto the wafer 25 from a concave mirror 220. In the case of a mask inspection system, the mask to be inspected can be placed instead of the wafer 25. The radiation reflected, diffracted, and / or refracted by the wafer 25 is directed onto a detector 23 for further evaluation by a concave mirror 221, which is also associated with the optical system 22. The radiation source 20 can provide a substantially continuous radiation spectrum, for example, by just one radiation source or a combination of several individual radiation sources. In a variation, one or more narrowband radiation sources can also be used. The wavelength or wavelength band is preferably in the range of 190 nm to 300 nm, and particularly preferably in the range of 190 nm to 200 nm. In addition to the two concave mirrors 220, 221, lenses can also be provided within the wafer or mask inspection system.

[0028] The optical element for the UV wavelength range proposed herein comprises an optical coating configured as a dielectric layer system on a substrate, the dielectric layer system comprising at least two different substrate layers having different refractive indices at certain wavelengths within the UV wavelength range, the layers of different substrates arranged alternately, and the optical element comprises a nanolayer system at the position of at least one of the substrate layers having a higher refractive index. For clarity, the nanolayer system is not shown in Figure 3, but its specific details are given in Figures 4 and 5.

[0029] Figure 3 schematically shows the configuration of an optical element 50 for the UV wavelength range, whose optical coating is based on a dielectric layer system 54. In this example, the dielectric layer system 54 is composed of alternating layers added to the substrate 51—for example, layers of substrate having a lower refractive index at the operating wavelength used for lithography exposure (also referred to as the lower refractive index layer 57) and layers having a higher refractive index at this operating wavelength (also referred to as the higher refractive index layer 58), with pairs of lower refractive index layer 57 and higher refractive index layer 56 forming a pair of layers 55. In this case, the thickness of the optical layer of the pair of layers 55 is usually selected to be close to half the incident wavelength in order to increase reflectance or transmittance. In this example, a protective layer 53 can be provided on the side of the dielectric layer system 54 away from the substrate, and this protective layer serves to protect the dielectric layer system 54 from external influences and can optionally consist of two or more layers. In modified examples not shown, a metal layer can be provided for the reflective coating between the substrate 51 and the dielectric layer system 54, which may be advantageous in particular for increasing reflectivity over a wide wavelength range. Depending on the material of the substrate 51, the layer in the dielectric layer system 54 closest to the substrate, or, if appropriate, the material of the metal reflective coating, it may be advantageous to provide an adhesion-promoting layer between them.

[0030] Figures 4 and 5 show enlarged views of the pair of layers 55, respectively. As already explained in relation to Figure 3, the pair of layers 55 comprises a layer 56 with a higher refractive index and a layer 57 with a lower refractive index. In this case, in the example shown herein, the layer 56 with the lower refractive index is the layer facing the substrate in the pair of layers 55. In another modification, the layer 57 with the higher refractive index can be the layer facing the substrate in the pair of layers 55. For transmissive optical elements, the substrate can be made of a material that is transparent to the radiation used, i.e., radiation within the UV wavelength range, with the UV wavelength range of 190 nm to 300 nm being particularly preferred, and the wavelength range of 190 nm to 200 nm being very particularly preferred. For reflective optical elements, dimensional stability and processability are more influential factors in material selection.

[0031] In both examples shown in Figures 4 and 5, the higher refractive index layer 57 is replaced by a single nanolayer system 71 in Figure 4 and by two nanolayer systems 72 and 73 in Figure 5, particularly affecting the absorbance of the higher refractive index layer 57, and specifically reducing its absorbance, thereby increasing its transmittance or reflectance and allowing less energy to enter the dielectric layer system. The individual layers 75 and 76 of the nanolayer systems 71, 72, and 73 have thicknesses in the nm range, while the layers 56 and 57 of the dielectric layer system have thicknesses in the 20-30 nm range. In the example shown in Figure 4, the substrate-facing side of the higher refractive index layer 57 is replaced by nanolayer system 71. In the example shown in Figure 5, the substrate-facing side of the higher refractive index layer 57 is replaced by nanolayer system 73, and the side away from the substrate is replaced by nanolayer system 72. In embodiments more preferred by production orders, in particular, nanolayer systems 72 and 73 are both composed of the same material. Selecting different materials for both nanolayer systems 72 and 73 offers greater potential for influencing the resulting absorbance and the refractive index of the higher refractive index layer 57. In both examples shown in Figures 4 and 5, the higher refractive index layer 57 is replaced by one or two nanolayer systems 71, 72, and 73 over more than half of its thickness. In variations, less than half of the higher refractive index layer may be replaced by a nanolayer system, or the entire higher refractive index layer may be replaced by one or more nanolayer systems. In particular, if two or more, most, or even all of the higher refractive index layers of the dielectric layer system consist of one or more nanolayer systems, different higher refractive index layers can be replaced by nanolayer systems to varying degrees.

[0032] In the example considered here, each of the nanolayer systems 71, 72, and 73 consists of two different nanolayer materials having different refractive indices at certain wavelengths within the UV wavelength range, and the respective layers 75 and 76 of these nanolayer systems are arranged alternately. It is highly advantageous to select the nanolayer materials with higher refractive indices and / or lower refractive indices to be the same material as the substrates of the dielectric layer systems, respectively, with higher refractive indices and / or lower refractive indices. As a result, a significant increase in refractive index or reflectivity can already be achieved, while minimizing the cost / complexity of adding optical coatings.

[0033] In particular, for optical elements with wavelengths in the range of 100 nm to 200 nm, preferably 190 nm to 200 nm, suitable substrates with a higher refractive index are oxides, such as Al2O3, MgAl2O4, and Lu3Al5O 12 Preferably, the material is one or more materials from the group consisting of GeO2, CaO, MgO, HfO2, Si3O4, Y2O3, and La2O3, which are mainly combined with silicon dioxide and / or amorphous fluoropolymers as substrates having lower refractive indices, such as commercially available Teflon® AF. For wavelengths in the range of 200 nm to 300 nm, ZrO2 and Ta5O5 are also suitable as materials with higher refractive indices, in particular. These can be combined not only with silicon dioxide and / or amorphous fluoropolymers as materials with lower refractive indices, but also with the higher refractive index materials described above up to 200 nm. The materials described above are particularly suitable as nanolayer materials with higher refractive indices and / or lower refractive indices, provided that the nanolayer materials with higher refractive indices and / or lower refractive indices are the same as the substrates with higher refractive indices and / or lower refractive indices, respectively.

[0034] Figure 6 shows the angle dependence of the reflectivity of a reflective optical element at an incident wavelength of 193 nm. The dashed curve B represents the reflectivity of a conventional reflective optical element with a dielectric layer system consisting of SiO2 as the lower refractive index material and Al2O3 as the higher refractive index material. This optical element is designed for quasi-normal incidence at a wavelength of 193 nm and has a nearly constant reflectivity of 97% up to an incident angle of 10° with respect to the surface normal. In contrast, the solid line A represents the reflectivity of a reflective optical element whose dielectric layer system similarly consists of SiO2 as the lower refractive index material and Al2O3 as the higher refractive index material, and is similarly designed for quasi-normal incidence at a wavelength of 193 nm, except that several Al2O3 layers are partially replaced by a nanolayer system. This nanolayer system is similarly composed entirely of alternating SiO2 and Al2O3 layers. As a result of this measure, the reflectivity of this optical element increased to just under 98%, which is only slightly more than 1% higher than that of conventional optical elements.

[0035] The configuration of such dielectric layer systems having nanolayers is shown in Figure 7. Starting from the left side of the substrate, the optical coating begins with a higher refractive index layer 57 of Al2O3, followed by a lower refractive index layer 56 of SiO2. In a rough framework, a total of 20 pairs of layers follow one another, with the higher refractive index layers being partially replaced by nanolayer systems 72 and 73, particularly at the third furthest point from the substrate, with more than half the thickness of each layer being replaced at the third furthest point from the substrate. Most of the higher refractive index layer 57 has nanolayer systems 72 made of Al2O3 and SiO2 on the side facing the substrate. In particular, at the third furthest point from the substrate in the coating, the higher refractive index layer 57 also has nanolayer systems 73 made of Al2O3 and SiO2 on the side away from the substrate. Towards the outer edge, the optical coating terminates with layer 72, which completely replaces the higher refractive index layers.

[0036] Figure 8 shows a plot of standing waves as the square of the absolute value of the electric field against the thickness of the optical coating, where these standing waves are formed during reflection by the optical element. A thickness of 0 nm is located at the interface between the dielectric layer system and the substrate. The total thickness of the dielectric layer system is approximately 1175 nm. The layer configuration in Figure 7 is sized and arranged so that the positions of the individual layers correspond to the configuration of the optical element in Figure 8. The nanolayer systems 72 and 73 are provided in a manner that targets points where the electric field within the layers with higher refractive indices is the external electric field (the maximum value in this plot), and therefore a particularly large amount of radiant energy is absorbed there. This strategy reduces the absorbance of the resulting optical element in a particularly effective way, and therefore not only increases the reflectance, or appropriately the transmittance, but also reduces the energy entering the dielectric layer system, thus reducing the probability of radiation damage.

[0037] Figure 9 shows the angular dependence of the reflectivity of another reflective optical element at an incident wavelength of 193 nm. The dashed curve B here again represents the reflectivity of a conventional reflective optical element, which has a dielectric layer system consisting of SiO2 as the lower refractive index material and Al2O3 as the higher refractive index material, is designed for quasi-normal incidence at a wavelength of 193 nm, and has a nearly constant reflectivity of 97% up to an incident angle of 10° with respect to the surface normal. In contrast, the solid line A represents the reflectivity of a reflective optical element whose dielectric layer system similarly consists of SiO2 as the lower refractive index material and Al2O3 as the higher refractive index material, and is similarly designed for quasi-normal incidence at a wavelength of 193 nm, except that several Al2O3 layers are partially replaced by a nanolayer system. This nanolayer system is entirely composed of alternating SiO2 and Al2O3 layers. As a result of this measure, the reflectivity of this optical element increased to just under 98%, which is an increase of just over 1% compared to conventional optical elements. The configuration of the corresponding layers is shown in Figure 10. There are a series of 20 pairs of layers, each comprising a nanolayer system 71 and a layer 56 of SiO2 with a lower refractive index. The nanolayer system 71 is composed of alternately arranged SiO2 layers and Al2O3 layers. Additional layers comprising nanolayer systems containing SiO2 and Al2O3 are arranged toward the outer periphery.

[0038] Figure 11 shows the configuration of another embodiment of the optical element proposed herein. This optical element is embodied as a reflective optical element and includes a metal layer 81 as part of the reflective coating. An adhesion-promoting layer 83 is provided between the substrate and the metal layer 81 for better adhesion. In the dielectric layer system, layers 56 with a lower refractive index and layers 57 with a higher refractive index are arranged alternately, and all of the layers 57 with a higher refractive index are partially replaced on the substrate side by a nanolayer system 71.

[0039] Figure 12 plots the reflectance of the coating shown in Figure 11 against the angle of incidence for incident radiation of 193 nm. A reflectance of over 97% is achieved in the incident angle range of 0° to 30°. Furthermore, the dielectric oxide layer protects the metal layer from ambient influences.

[0040] In optical systems comprising two or more optical elements, the amount of radiation processed through each optical system can be visibly increased by the procedure proposed here, resulting in a doubling of reflectivity or transmittance. As a result of less energy entering the dielectric layer system of the optical system, the probability of radiation damage decreases for each individual optical element.

[0041] It should be noted that the preferred embodiments described herein, with reference to Figures 6-11, are based on SiO2 as a lower refractive index material and Al2O3 as a higher refractive index material. However, the effects described are also achieved with materials for the higher refractive index layer and other layers, such as MgAl2O4, Lu3Al5O 12 Other oxide layer materials such as GeO2, CaO, MgO, HfO2, Si3N4, Y2O3, or La2O3, or Al2O3, MgAl2O4, Lu3Al5O as part of the material for the higher refractive index layer and other layers. 12This could also be achieved with two or more materials from the group consisting of GeO2, CaO, MgO, HfO2, Si3N4, Y2O3, or La2O3, and with Teflon® AF or SiO2, for example, as a material with a lower refractive index or as SiO2, and / or as part of a layer of a material with a lower refractive index and other layers. Even in the case of optical elements designed for use in transmission rather than reflection, an increase in transmittance could be observed, in particular, if the optical element does not have a nanolayer system at the position of the layer furthest from the substrate.

[0042] Due to their improved transmittance or reflectance and lifespan, the optical elements described herein are particularly suitable for use in lithography equipment for the UV wavelength range, or in optical systems for mask or wafer inspection equipment, and also for use in optical systems used with lasers in the UV wavelength range. [Explanation of symbols]

[0043] 1. VUV (vacuum UV) lithography system 2. Wafer inspection system 3. Reflective optical elements 4. Reflective optical elements 5. Reflective optical elements 6. Reflective optical elements 10 Radiation source 11 Radiation 12 Lighting Systems 13 masks 14 Projection system 15 Exposed elements 20 Radiation source 21 Radiation 22 Optical system 23 Detectors 25 wafers 50 Optical elements 51 circuit boards 53 Protective layer 54 Dielectric layer system 55 layers Layers with a refractive index lower than 56 57 Layers with a higher refractive index 60 Electric field strength 61 Minimum electric field strength 62 Maximum electric field strength 71 nanolayer system 72 nanolayer system 73 nanolayer system 75 layers 76 layers 81 Metal layer 83 Adhesion promotion layer 120 lenses 121 Mirror 140 lenses 141 Lens 220 Mirror 221 Miller 1210 Reflective surface

Claims

1. An optical element for the ultraviolet (UV) wavelength range, comprising a substrate and an optical coating configured as a dielectric layer system, wherein the dielectric layer system comprises at least two different substrate layers having different refractive indices at one wavelength within the UV wavelength range, and the layers of the different substrates are arranged alternately in the optical element, An optical element characterized in that the optical element (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) has a nanolayer system (71, 72, 73) at the position of at least one layer (57) of the substrate having a higher refractive index.

2. The optical element according to claim 1, characterized in that at least one layer (57) of the substrate having a higher refractive index is at least partially replaced by the nanolayer system (71, 72, 73).

3. The optical element according to claim 1 or 2, characterized in that the optical elements (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) are designed for wavelengths of 190 nm to 300 nm.

4. The optical element according to any one of claims 1 to 3, characterized in that the at least one nanolayer system (71, 72, 73) is composed of at least two different nanolayer materials (75, 76) having different refractive indices at one wavelength within the UV wavelength range, and the different nanolayer materials are arranged alternately.

5. The optical element according to claim 4, characterized in that the nanolayer material having a higher refractive index and / or a lower refractive index is the same material as the substrate having a higher refractive index and / or a lower refractive index, respectively.

6. The substrate having a refractive index higher than the above is Al 2 O 3 、MgAl 2 O 4 、Lu 3 Al 5 O 12 、GeO 2 、CaO, MgO, HfO 2 、Si 3 N 4 、Y 2 O 3 、La 2 O 3 The optical element according to any one of claims 1 to 5, characterized in that it is one or more of the materials in the group consisting of

7. The optical element according to any one of claims 1 to 6, characterized in that the substrate having a lower refractive index is silicon dioxide and / or an amorphous fluoropolymer.

8. The optical element according to any one of claims 1 to 7, characterized in that the optical coating is designed as a reflective coating, and at least one layer (57) comprising the nanolayer system comprises the nanolayer system located in the optical coating (54) at the third furthest point from the substrate.

9. The optical element according to any one of claims 1 to 8, characterized in that the optical element (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) has the nanolayer system (71, 72, 73) at at least one of the seven layers having a higher refractive index that are located furthest from the substrate.

10. The optical element according to claim 9, characterized in that the optical elements (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) have the nanolayer system (71, 72, 73) at all positions of each of the three, four, five, six, or seven layers having a higher refractive index and located furthest from the substrate.

11. The optical element according to any one of claims 1 to 10, characterized in that the optical coating is designed as a reflective coating, and the substrate-facing side of at least one of the layers (57) having a higher refractive index is replaced by the nanolayer system (71, 72).

12. The optical element according to any one of claims 1 to 7, characterized in that the optical coating is designed as an anti-reflective coating, and the optical elements (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) do not have the nanolayer system at the position of the layer furthest from the substrate.

13. The optical element according to any one of claims 1 to 12, characterized in that both the side of at least one of the layers (57) having a higher refractive index that faces the substrate and the side that is away from the substrate are replaced by the nanolayer system (72, 73).

14. The optical element according to claim 13, characterized in that both of the nanolayer systems are made of the same material.

15. The optical element according to any one of claims 1 to 14, characterized in that at least half of the at least one layer (57) having a higher refractive index is replaced by the nanolayer system (71, 72, 73).

16. An optical element according to any one of claims 1 to 15, characterized in that a standing wave of an electric field is formed when reflection is performed within the UV wavelength range, and the optical element (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) has the nanolayer system (71, 72, 73) at a point where the external electric field strength of the standing wave exists in at least one of the layers (57) having a higher refractive index.

17. An optical system comprising the optical elements (3, 4, 5, 6, 13, 50, 120, 121, 140, 141, 220, 221) according to any one of claims 1 to 16.

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