Lens element of a microlithography projection exposure apparatus designed to operate under DUV, and method and apparatus for forming an anti-reflective layer.

Abstract

The present invention relates to a lens element of a microlithography projection exposure apparatus designed to operate with DUV, and a method and apparatus for forming an antireflection layer. According to one aspect, in the case of the lens element (100) according to the present invention, an antireflection layer (102, 302) is formed on the lens substrate, and the antireflection layer (102, 302) includes a first material having a relatively low refractive index and a second material having a relatively high refractive index, and the mixing ratio of the first material and the second material changes in the lateral direction and / or the longitudinal direction.

Description

Technical Field

[0001] This application claims the priority of German Patent Application No. 10 2022 207 068.2 filed on July 11, 2022. The content of this German application is incorporated herein by reference.

[0002] The present invention relates to a lens element of a microlithography projection exposure apparatus designed to operate in DUV, and a method and apparatus for forming an antireflection layer.

Background Art

[0003] Microlithography is used in the manufacture of microstructured electronic devices. The microlithography process is carried out in a so-called projection exposure apparatus including an illumination device and a projection lens. An image of a mask (reticle) illuminated by the illumination device is projected onto a substrate (e.g., a silicon wafer) coated with a photosensitive layer (photoresist) and arranged on the image plane of the projection lens by the projection lens, so as to transfer the mask structure to the photosensitive coating of the substrate.

[0004] In the case of an antireflection layer used for a lens element in the DUV region (i.e., for example, about 365 nm, about 248 nm, or about 193 nm), its realization becomes a severe problem considering the increasing requirements regarding the lithography system (e.g., regarding minimizing wavefront aberration while providing the best antireflection effect over a wide wavelength range). FIGS. 5a and 5b show schematic diagrams for explaining a conventional method of forming an antireflection layer on a lens element substrate 501, in which sub-layers 502a, 502b of materials having different refractive indices from separate evaporation sources 511, 512 are alternately coated. The actual problem is that the increase in the number of sub-layers in the layer configuration of the antireflection layer is limited due to the undesirable effects of an accompanying increase in thickness (especially an increase in radiation absorption and resulting refractive index fluctuations or wavefront aberration, and an increase in the deformation effect of the antireflection layer due to an increase in line tension).

[0005] Figure 6 schematically illustrates yet another problem that actually arises in terms of manufacturing when forming an anti-reflective layer on a curved (e.g., spherical) lens element. During the formation of the anti-reflective layer 602 on the lens element substrate 601 (which rotates around a spin rotation axis during the coating process, as shown in Figure 6), the material applied by the evaporation source 610 strikes the lens element edges at a considerably larger deposition angle with respect to each surface normal than the center of the lens element, so the above formation of the anti-reflective layer at the lens element edges occurs with a relatively high porosity. This situation further affects the layer thickness profile (which is usually set based on adding a desired mass in the coating process). In the absence of an aperture effect, the layer thickness at the lens element edges is smaller than at the center of the lens element, but the porosity is higher, and therefore the layer thickness is not as small as geometrically expected, as the layer thickness depends on the cosine of the deposition angle when the material density at the center and the material density at the edges are the same. This undesirable effect can be counteracted by redistributing the material across the lens element surface using a shielding aperture, as shown in Figures 7a to 7d. However, the optical performance remains impaired, particularly because the refractive index decreases towards the lens element edges due to the porosity mentioned above. By increasing the layer thickness at the lens element edges compared to the center of the lens element, the reflection loss and polarization separation values ​​at the lens element edges can be approximated to those at the center. However, since the refractive index at the lens element edges is lower, the optical performance of the anti-reflective layer at the center of the lens element cannot be fully achieved. For example, according to Figures 7a to 7d, a 7% thicker anti-reflective layer with a more porous and therefore lower refractive index sublayer exhibits higher transmission loss due to reflection and higher polarization separation at large incident angles compared to the anti-reflective layer at the center of the lens element.

[0006] For the latest technologies, please refer to Patent Document 1, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2 as examples. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] German Patent Application Publication No. 10 2016 200 814 [Patent Document 2] German Patent Application Publication No. 10 2012 215 359 Specification [Non-patent literature]

[0008] [Non-Patent Document 1] MF Schubert et al.: “Performance of antireflection coatings consisting of multiple discrete layers and comparison with continuously graded antireflection coatings”, Applied Physics Express 3 (2010) 082502-1 to 082502-3 [Non-Patent Document 2] M. Jupe et al.: “Laser-induced damage in gradual index layers and rugate filters”, Proc. OF SPIE Vol. 6403,: 2006, 640311-1 to 640311-13 (15. Jan. 2007); doi: 10.1117 / 12.696130 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a lens element for a microlithography projection exposure apparatus designed to operate under DUV, and a method and apparatus for forming an anti-reflective layer, which enable improved optical performance while at least partially avoiding the above-mentioned problems. [Means for solving the problem]

[0010] This objective is achieved by the features described in the independent patent claims.

[0011] According to one aspect, the present invention relates to a lens element for a microlithography projection exposure apparatus designed to operate under DUV, An anti-reflective layer is formed on the lens element substrate of the above lens element, The anti-reflective layer has a first material with a relatively low refractive index and a second material with a relatively high refractive index, This invention relates to a lens element in which the mixing ratio of a first material and a second material changes in the lateral and / or vertical directions.

[0012] The present invention is particularly based on the concept of designing an anti-reflective layer on a lens element intended for use in a microlithography projection exposure apparatus designed to operate under DUV, comprising a relatively low refractive index material and a relatively high refractive index material, such that the mixing ratio of these materials varies in the lateral and / or vertical directions.

[0013] In this text and the following, “lateral direction” is understood to mean the direction parallel to the layer (i.e., along the surface of the anti-reflective layer), and “longitudinal direction” is understood to mean the direction perpendicular to the plane of the layer or the transverse plane (i.e., the direction of the stacking direction).

[0014] The present invention includes, firstly, embodiments in which the above-mentioned change in the mixing ratio is achieved by simultaneous deposition (co-deposition) from separate evaporation sources having different evaporation rates, and this change in the evaporation rate of each of the two materials is accompanied by a change in the lens element substrate region coated from the center of the lens element toward the edge of the lens element, respectively. With this method, as will be described in more detail below, the undesirable effect of the porosity of the anti-reflective layer increasing towards the edge of the lens element due to manufacturing can be compensated for by the undesirable decrease in refractive index near the edge of the lens element due to the increase in porosity being counteracted by increasing the corresponding evaporation rate of the high-refractive-index material.

[0015] Furthermore, the present invention also includes embodiments in which the above-mentioned change in the mixing ratio is performed in the vertical direction (i.e., perpendicular to the transverse direction), thereby achieving the best anti-reflective effect over a relatively large incident angle range with a relatively small total thickness of the anti-reflective layer (and thus avoiding the problems associated with the aforementioned large total layer thickness). For this setting of the mixing ratio changing in the vertical direction, the present invention further includes embodiments in which the change in the mixing ratio of the materials according to the present invention is achieved by setting the shutter opening period assigned to each evaporation source as desired, while ensuring that the evaporation of each material is performed at a constant evaporation rate, thereby avoiding the difficulties that arise in variable closed-loop control of the evaporation rate.

[0016] In other words, according to the present invention, by appropriately synchronized switching between the open and closed states of the shutter for each material (i.e., a high refractive index material on the one hand and a low refractive index material on the other), the evaporation rate of each separate evaporation source itself remains constant over time, but the effective evaporation rate is set which changes with time or with the gradual formation of the anti-reflective layer.

[0017] In this case, the two concepts mentioned above—namely, compensating for the effect of increasing porosity towards the lens element edge during anti-reflective layer formation, and on the other hand achieving the best anti-reflective effect over a wide incident angle range with a relatively small total thickness of the anti-reflective layer—can be combined to each other's advantage. For example, in an anti-reflective layer designed for a wavelength of 365 nm, the decrease in refractive index of the high-refractive-index Al2O3 sublayer from n0=1.72 at the center of the lens element to n1=1.52 at the lens element edge (see also Figure 7a) can be compensated for by co-deposition of HfO2 with a refractive index of 2.1, thus achieving the same optical performance as the center of the lens element (Figures 7b and 7c). As the porosity increases towards the lens element edge, the refractive index of HfO2 also decreases by 12% from a value of 2.1 to a value of n2 = 1.85 at the lens element edge, in the same ratio as Al2O3. Therefore, a mixing ratio of 60% HfO2 to 40% Al2O3 must be selected at the lens element edge (the refractive index obtained according to the mixing ratio x = 0.6 is (1-x)). * n1+x *(due to n2 substantially corresponding to the value n0 = 1.72 of Al2O3 at the center of the lens element).

[0018] Therefore, the present invention particularly relates to, on the one hand, embodiments in which, by compensating for the porosity that increases towards the edge of the lens element and changing the mixing ratio of the high-refractive-index material and the low-refractive-index material in the lateral direction, substantially constant optical performance (particularly, a constant average refractive index) is achieved over the entire surface of the lens element from the center of the lens element to the edge of the lens element, and further, embodiments in which, by changing the mixing ratio of the high-refractive-index material and the low-refractive-index material in the longitudinal direction (using the above-described synchronous opening and closing of shutters at a constant evaporation rate of separate evaporation sources), a good antireflection effect is achieved over a wide incident angle range with a relatively small total thickness of the antireflection layer.

[0019] According to one embodiment, the lens element has at least one curved lens element surface. In particular, the lens element can also be a cylindrical lens element.

[0020] The present invention also relates to a microlithography projection exposure apparatus having at least one lens element having the above-described characteristics.

[0021] The present invention further relates to a method of forming an antireflection layer on a lens element substrate of a lens element of a microlithography projection exposure apparatus designed to operate in DUV, where the antireflection layer is formed from a first material having a relatively low refractive index and at least one second material having a relatively high refractive index, and relates to a method in which the mixing ratio of the first material and the second material changes in the lateral direction and / or the longitudinal direction.

[0022] According to one embodiment, the antireflection layer is formed using separate evaporation sources for the first material and the second material that supply each material through shutters that open intermittently.

[0023] According to one embodiment, the evaporation source operates at a constant evaporation rate, and the change in the mixing ratio is achieved by setting the opening period of the shutter as desired.

[0024] According to one embodiment, simultaneous deposition from an evaporation source is performed, and the increase in the evaporation rate of the second material compared to the evaporation rate of the first material is synchronized with the changes in each region within the coating of the lens element substrate. This synchronization makes it possible to increase the evaporation rate of the second material, in particular, from the central region of the lens element to the edge region of the lens element, compared to the evaporation rate of the first material.

[0025] According to one embodiment, changes in each coating region of the lens element substrate are achieved by changing the relative position of the aperture diaphragm positioned at the shielding diaphragm with respect to the lens element.

[0026] The present invention further relates to an apparatus for forming an anti-reflective layer on a lens element substrate of a lens element of a microlithography projection exposure apparatus designed to operate under DUV, The system comprises a first evaporation source for a first material with a relatively low refractive index and a second evaporation source for a second material with a relatively high refractive index. A separate shutter is assigned to the first evaporation source and the second evaporation source, and This relates to a device equipped with a mechanism for intermittently opening these shutters.

[0027] According to one embodiment, the device further comprises a shielding aperture and a device for changing the relative position of the aperture diaphragm positioned at the shielding aperture with respect to the lens element.

[0028] According to one embodiment, the device is configured to change the position of the aperture diaphragm relative to the lens element in synchronization with an increase in the evaporation rate of the second material compared to the evaporation rate of the first material.

[0029] Further embodiments of the present invention will become apparent from the description and dependent claims.

[0030] The present invention will be described in more detail below with reference to exemplary embodiments shown in the attached drawings. [Brief explanation of the drawing]

[0031] [Figure 1] A schematic diagram illustrating a method for forming an anti-reflective layer on a lens element substrate according to one embodiment of the present invention is shown. [Figure 2] A schematic diagram illustrating a method for forming an anti-reflective layer on a lens element substrate according to one embodiment of the present invention is shown. [Figure 3] A schematic diagram illustrating a method for forming an anti-reflective layer on a lens element substrate according to yet another embodiment of the present invention is shown. [Figure 4] A schematic diagram illustrating possible configurations of a microlithography projection exposure system designed to operate under DUV conditions is shown. [Figure 5] Figures a and b show schematic diagrams illustrating a conventional method for forming an anti-reflective layer on a lens element substrate. [Figure 6] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Figure 7a] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Figure 7b] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Figure 7c] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Figure 7d] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Figure 8a] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Figure 8b] This diagram illustrates the problems that arise in conventional methods for forming an anti-reflective layer on a lens element substrate. [Modes for carrying out the invention]

[0032] The following text describes various embodiments of implementing an anti-reflective layer on a lens element substrate for lens elements intended for use in a microlithography projection exposure system designed to operate under DUV. These embodiments share in common that the mixing ratio of a first material with a relatively low refractive index and a second material with a relatively high refractive index is varied, and this variation occurs laterally and / or longitudinally, depending on the exemplary embodiment, during the formation of the anti-reflective layer.

[0033] Figures 1 and 2 first show schematic diagrams illustrating a method for forming an anti-reflective layer on a lens element substrate indicated by "101". A first evaporation source 111 having a first material with a relatively low refractive index and a second evaporation source 112 having a second material with a relatively high refractive index are used. The formation of the anti-reflective layer indicated by "102" is carried out by forming a mixing ratio that changes in the lateral direction. Materials with a relatively low refractive index include MgF2, AlF3, SiO2, and thiolite (Na5Al3F 14 ), or cryolite (Na3AlF6). Materials with relatively high refractive indices that can be used are LaF3, or oxide materials such as Al2O3, HfO2, TiO2, or ZrO2, depending on the wavelength used in the optical system or projection exposure apparatus. Preferably, high refractive index fluoride materials should be mixed with low refractive index fluoride materials, and high refractive index oxide materials should be mixed with low refractive index oxide materials.

[0034] The formation of a laterally varying mixing ratio is firstly achieved by shifting the shielding aperture 120 during the coating process (the lens element substrate 101 rotates around a spin rotation axis as shown in Figure 2), thereby changing the relative position of the aperture aperture 120a positioned on the shielding aperture 120 with respect to the lens element substrate 101, and simultaneously (i.e., in synchronization with the above change in relative position and the associated changes in the regions within each coating from the center to the edge of the lens element), the evaporation rates of the first and second materials are changed. In this embodiment, the lens element 100, including the lens element substrate 101 and the anti-reflective layer 102, can also be a cylindrical lens element (extending in the plane from Figure 2), in which case the aforementioned rotation of the lens element substrate 101 is omitted.

[0035] Typical evaporation rates for appropriate thermal deposition processes such as electron beam deposition and heated boat deposition are in the range of 0.05 nm / s to 2 nm / s, preferably 0.2 nm / s to 0.5 nm / s. For wavelengths in the range of 193 nm to 365 nm, the single-layer thickness of the anti-reflective coating is in the range of 2 nm to 200 nm, preferably 30 nm to 60 nm. This means that, with a typical coating time of 60 to 300 seconds and an aperture diaphragm 120a with a diameter of 10 mm, the shift at the center of the lens element occurs at a speed of 10 mm to 2 mm per minute, and correspondingly slows down towards the edges of the lens element.

[0036] If we denote the evaporation rate of the first material as α, the refractive index of the first material as n1, the evaporation rate of the second material as β, and the refractive index of the second material as n2, then the refractive index of the resulting anti-reflective layer will be as follows:

[0037]

number

[0038] The evaporation rates α and β are adjusted so that the evaporation rate of the second material, which has a relatively high refractive index, increases as it approaches the lens element edge relative to the evaporation rate of the low refractive index material. As a result, the aforementioned undesirable effect of increased porosity due to the larger deposition angle towards the lens element edge can be compensated for in terms of the effect on the average refractive index obtained by the lens element and, consequently, its optical performance.

[0039] At the same time, undesirable thickness variations during the formation of the anti-reflective layer can be reduced, which are usually caused by the fact that the target mass, which is important for the completion of the coating process, is only achieved later, and therefore only when the thickness is large, as the porosity increases towards the lens element edge. If the high refractive index material used according to the present invention is selected to be denser than the low refractive index material, the target mass suitable for the completion of the sealing process is also achieved earlier towards the lens element edge, thereby compensating for the aforementioned thickness profile.

[0040] Figure 3 shows a schematic diagram illustrating yet another exemplary embodiment in which the mixing ratio change according to the present invention is performed longitudinally, with the aim of achieving maximum anti-reflective effect over a wide incident angle range with a relatively small total layer thickness of the anti-reflective layer, as shown in Figures 8a to 8c. In the case of a microlithography projection exposure apparatus, the normal incident angle range can be 0° to 60°, and the reflectance should not exceed 0.1% up to an incident angle of 30°. To avoid heating of the lens element due to layer absorption, deformation of the lens element due to layer stress, and crack formation of the layer, the total layer thickness should be less than 200 nm, preferably less than 100 nm.

[0041] As shown in Figure 3, the mixing ratio is changed by intermittently shielding each evaporation source (indicated as "311" in Figure 3), and the opening periods of each shutter used for this purpose can be set as desired. As a result, even when the evaporation source 311 is operated at a constant evaporation rate, the "effective rate" at which the material is supplied to the lens element substrate 301 for the formation of the anti-reflective layer 302 changes.

[0042] When the shutter opens during period t1 and closes during period t2, the following effective rates are obtained with a constant evaporation rate β of the evaporation source 311.

[0043]

number

[0044] By appropriately setting the ratio of the open period t1 (when deposition takes place on the lens element substrate 301) to the shielded period t2, it is possible to set any effective speed from 0 to a constant value β according to the rate of the evaporation source 311. In this case, since the switching of the shutter opening and closing is performed very quickly, it is preferable that approximately one atomic monolayer of the material is coated in one cycle. In this case, a substantially continuous gradient mixed layer can be made from different materials. At a normal evaporation rate of 0.05 nm to 0.2 nm per second, the switching of the shutter opening and closing must be performed every 1 to 4 seconds.

[0045] Using separate evaporation sources, each at a constant evaporation rate, is advantageous because it avoids the difficulties typically associated with continuous closed-loop evaporation rate control.

[0046] As described above, even in the case of lens elements that may have strong curvature, the lateral change in the mixing ratio of the high-refractive-index material and the low-refractive-index material according to the present invention (from the center of the lens element to the edge of the lens element) can be combined with the longitudinal change in the mixing ratio of the high-refractive-index material and the low-refractive-index material to achieve substantially constant optical performance across the lens element surface from the center to the edge of the lens element (as a result in the "lateral direction"), and to achieve a good anti-reflective effect over a wide incident angle range with a relatively small total thickness of the anti-reflective layer (as a result in the "longitudinal direction").

[0047] Here, starting with the embodiment described with reference to Figure 2, and then as described above with reference to Figure 3, it is possible to create a gradient mixed layer of different materials with varying mixing ratios in the vertical direction (see Figure 8a) while the shielding aperture 120 is temporarily fixed or the position of the aperture aperture 120a positioned on the shielding aperture 120 is temporarily constant.

[0048] Figure 4 shows the configuration of a microlithography projection exposure system 400 designed to operate under DUV, which is possible in principle.

[0049] The projection exposure apparatus 400 shown in Figure 4 comprises an illumination device 410 and a projection lens 420. The illumination device 410 is used to illuminate the structural support mask (reticle) 415 with light from a light source unit 405, which includes a laser light source in the form of, for example, an ArF excimer laser for a wavelength of 193 nm (or a KrF excimer laser for a wavelength of 248 nm or a mercury lamp for a wavelength of 365 nm) and a beam shaping optical unit that generates a parallel light beam. The laser light source can be designed according to the present invention.

[0050] The illumination device 410 has an optical unit 411, which in the illustrated example includes a deflection mirror 412 in particular. The optical unit 411 includes, for example, a diffractive optical element (DOE) and a zoom axicon system to generate different illumination settings (i.e., intensity distributions of the pupil surface of the illumination device 410). Downstream of the optical unit 411 in the beam path in the direction of light propagation, there is an optical mixing device (not shown) which may have, for example, a known arrangement of micro-optical elements suitable for achieving light mixing, and a group of lens elements 413. Downstream therefrom, a field of view including a reticle masking system (REMA) is positioned, and the field of view is imaged onto a structure-supported mask (reticle) 415 positioned on another field of view by a REMA lens 414 that continues in the direction of light propagation, thus defining the illumination region on the reticle. The structure-supported mask 415 is imaged onto a lens element substrate or wafer 430 having a photosensitive layer (photoresist) using a projection lens 420. The projection lens 420 may be specifically designed for immersion operation, in which case the immersion medium is positioned upstream of the wafer or its photosensitive layer with respect to the direction of light propagation. Furthermore, the projection lens may have a numerical aperture NA greater than, for example, 0.85, and particularly greater than 1.1.

[0051] Although the present invention is also described by certain embodiments, those skilled in the art will recognize multiple variations and alternative embodiments, for example, by combinations and / or substitutions of features of the individual embodiments. Accordingly, it will be understood that such variations and alternative embodiments are also included in the present invention, and the scope of the present invention is limited only to the meaning of the appended claims and their equivalents.

Claims

1. A lens element for a microlithography projection exposure apparatus designed to operate under DUV conditions, An anti-reflective layer (102, 302) is formed on the convex surface of the lens element substrate (101, 301) of the lens element (100) by deposition from an evaporation source. The anti-reflective layer (102, 302) comprises a first material with a relatively low refractive index and a second material with a relatively high refractive index, The mixing ratio of the first material and the second material changes both in the transverse direction along the surface of the anti-reflective layer (102, 302) and in the vertical direction perpendicular to the transverse plane. The ratio of the second material is increased towards the edge of the lens element (100). A lens element in which the reflectivity does not exceed 0.1% up to an incident angle of 30°, and the total layer thickness is less than 200 nm.

2. A lens element according to claim 1, characterized in that it has at least one curved lens element surface.

3. A microlithography projection exposure apparatus comprising at least one lens element according to claim 1 or 2.

4. A method for forming an anti-reflective layer (102, 302) on the convex surface of a lens element substrate (101, 301) of a lens element of a microlithography projection exposure apparatus (400) designed to operate under DUV conditions, The anti-reflective layer (102, 302) is formed from a first material having a relatively low refractive index and at least one second material having a relatively high refractive index. The mixing ratio of the first material and the second material changes in the transverse direction along the surface of the anti-reflective layer (102, 302) and in the vertical direction perpendicular to the transverse plane. The anti-reflective layers (102, 302) are formed by vapor deposition using separate evaporation sources for the first and second materials, and the materials from the evaporation sources are supplied via intermittently opening shutters, respectively. The evaporation rate of the second material increases relative to the evaporation rate of the first material as it approaches the edge of the lens element. A method in which the reflectance does not exceed 0.1% up to an incident angle of 30°, and the total layer thickness is less than 200 nm.

5. The method according to claim 4, characterized in that the lens element (100) has at least one curved lens element surface.

6. The method according to claim 4 or 5, characterized in that the evaporation source is operated at a constant evaporation rate, and the change in the mixing ratio is achieved by setting the opening periods of the shutters assigned to each evaporation source to a target.

7. The method according to claim 4 or 5, characterized in that simultaneous evaporation from the evaporation sources (111, 112) is performed, and the increase in the evaporation rate of the second material compared to the evaporation rate of the first material is synchronized with the change in the region in each coating of the lens element substrate (101, 301).

8. The method according to claim 7, characterized in that, during the same period, the evaporation rate of the second material increases in the direction from the central region of the lens element (100) to the edge region of the lens element (100) compared to the evaporation rate of the first material.

9. The method according to claim 7, characterized in that the change in the region of the coating on the lens element substrate (101, 301) is performed by a change in the relative position of the aperture diaphragm (120a) positioned on the shielding diaphragm (120) with respect to the lens element (100).

10. An apparatus for forming an anti-reflective layer (102, 302) on the convex surface of a lens element substrate (101, 301) of a lens element of a microlithography projection exposure apparatus (400) designed to operate under DUV conditions, The system comprises a first evaporation source for a first material with a relatively low refractive index and a second evaporation source for a second material with a relatively high refractive index. A separate shutter is assigned to the first evaporation source and the second evaporation source, and A device is provided to intermittently open the shutter. The apparatus is configured such that the mixing ratio of the first material and the second material changes both in the transverse direction along the surface of the anti-reflective layer (102, 302) and in the vertical direction perpendicular to the transverse plane, the evaporation rate of the second material increases relative to the evaporation rate of the first material as it approaches the edge of the lens element, the reflectivity of the anti-reflective layer (102, 302) does not exceed 0.1% up to an incident angle of 30°, and the total layer thickness is less than 200 nm.

11. The apparatus according to claim 10, further comprising a shielding aperture (120) and a device for changing the relative position of an aperture diaphragm (120a) positioned on the shielding aperture (120) with respect to the lens element (100).

12. The apparatus according to claim 11, characterized in that the position of the aperture diaphragm (120a) relative to the lens element (100) is changed in synchronization with an increase in the evaporation rate of the second material compared to the evaporation rate of the first material.

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