Method for manufacturing an optical element

Abstract

The optical element (11) has an optical surface (20) with a diffractive structure (21). The optical surface (20) is curved such that the ratio of the distance A between the lowest point (T) and the highest point (H) to the maximum diameter D exceeds 1 / 10. When manufacturing the optical element (11), a raw optical element having a raw optical surface on which the diffractive structure (21) is to be formed is first prepared. The raw optical surface is then coated with photoresist using an isotropic deposition method, and the photoresist is exposed and then developed. This provides a method for manufacturing an optical element having an optical surface with a diffractive structure that meets strict requirements for structural accuracy during the manufacturing of the diffractive structure.

Description

[Technical Field]

[0001] This patent application claims priority from German Patent Application No. 10 2020 206 107.6, the content of which is incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing an optical element having an optical surface with a diffractive structure, and further to an optical element manufactured by said method, an illumination system comprising said optical element, a projection exposure apparatus comprising said illumination system, a method for manufacturing a microstructured or nanostructured component using said projection exposure apparatus, and a microstructured or nanostructured component manufactured by said method. [Background technology]

[0003] An example of an optical element having a curved optical surface in which the distance-to-diameter ratio between the distance between the deepest and highest points on the optical surface and the maximum diameter measured along the mean surface normal exceeds 1 / 10 is a collector for an EUV beam as part of the illumination system of an EUV projection exposure tool. An example of such a collector is known to those skilled in the art from US Pat. No. 5,623,999. The reflective surface of the collector of US Pat. No. 5,623,999 is manufactured using a diamond turning method.

[0004] Patent Document 2 discloses a method for coating curved surfaces by spray coating. In principle, such a method can be used to apply photoresist for producing diffractive structures on optical surfaces. However, as long as diffractive structures must be produced with strict requirements for structural precision, the spray coating method faces limitations.

[0005] See further the prior art below. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 9,541,685 [Patent Document 2] U.S. Patent No. 6,352,747 [Patent Document 3] Special Publication No. 8-146209 [Patent Document 4] Detailed information of the application for exclusive patent No. 10 2016 209 359 [Patent Document 5] Detailed information on the application for exclusive patent No. 10 2017 221 746 [Patent Document 6] Detailed information on the application for exclusive patent No. 10, 2019, 214, 243

Non-licensed literature

[0007]

Non-patent document 1

Non-patent document 2

Non-patent document 3

Non-patent document 4

[0008] An object of the present invention is to develop a method for manufacturing an optical element having an optical surface with a diffractive structure, which satisfies strict requirements for structural precision during the manufacturing of the diffractive structure. [Means for solving the problem]

[0009] This object is achieved according to the invention by a manufacturing method having the features of claim 1.

[0010] For the optical element to be manufactured, the distance-to-diameter ratio A / D can be greater than 1 / 8, greater than 1 / 5, greater than 1 / 4, greater than 1 / 2, or even greater than 1 / 1. The upper limit of the distance-to-diameter ratio can be 1 / 1. The mean surface normal is the directional average value averaged over the directions of all normals to the surface portions of the optical surface. For a rotationally symmetric optical surface having boundary surfaces that are also rotationally symmetric with respect to the axis of rotational symmetry, the direction of the mean surface normal corresponds to the direction of the axis of rotational symmetry.

[0011] The optical surface of the optical element can be a reflective surface. Alternatively, the optical surface can be a refractive surface. The raw distance-to-diameter ratio of the raw optical surface can deviate by no more than 10% from the distance-to-diameter ratio A / D of the fabricated optical surface. With respect to its convex / concave curvature, the raw optical surface can have a base curvature that corresponds to the base curvature of the optical surface of the fabricated element.

[0012] Before coating the raw optical surface with photoresist, the substrate of the raw optical surface can be coated with a structurable layer, and then diffractive structures are introduced therein. First, coating the substrate with a structurable layer and second, developing the photoresist are known from the prior art. For these steps, which are not different in principle from the prior art spray coating using a photoresist coating step, see the technical articles by Pham et al., "Spraycoating of photoresist for pattern transfer on high topography surfaces," J. Micromech. Microeng. 15 (2005) 691 to 697, and by Yu et al., "Spraycoating of photoresist for 3D microstructures with different geometries," Journal of Physics: Conference Series 34 (2006) 937 to 942.

[0013] Following the development of the photoresist, the photoresist residues can be removed. Coating with photoresist and developing the photoresist can also be repeated in sequence during the manufacturing method. As is also known from the prior art, after the manufacturing of the diffractive structure, it can be encapsulated with an encapsulating layer.

[0014] The isotropic deposition method ensures a uniform conformal coating of the raw optical surface with photoresist. The structures already present on the raw optical surface are maintained in the photoresist without being blurred or blurred during coating. The isotropic, uniform coating also ensures that areas that are difficult or impossible to access using conventional directional coating methods are also coated with photoresist as desired. If desired during a subsequent photoresist coating step, the structure sidewalls of the optical diffraction structure already produced in a previous step can also be isotropically coated with photoresist to the desired layer thickness. This is possible even if the already existing structure sidewalls have high sidewall steepness. The isotropic deposition method is particularly independent of gravity.

[0015] The coating thicknesses according to claim 2 have proven to be practically significant. The absolute coating thickness of the photoresist can be in the range of 5 μm to 15 μm, in the range of 6 μm to 12 μm, in the range of 8 μm to 10 μm. The thicknesses can in particular be 8 μm, 9 μm and 10 μm.

[0016] The thickness variation of the photoresist applied by the isotropic deposition method of claim 3 allows the photoresist to be subsequently developed very clearly, regardless of the thickness effect of the photoresist. The thickness variation, i.e., the difference between the maximum and minimum photoresist thickness, in a given portion of a given surface, particularly across the entire optical surface where the diffractive structure is to be applied, can be less than 15%, less than 10%, or even less than 5%. The thickness variation is typically greater than 1%. The absolute thickness variation of the applied photoresist can be less than 2 μm. This applies particularly to absolute photoresist thicknesses greater than 10 μm. The thickness variation can even be significantly less than 2 μm, less than 1.5 μm, less than 1.0 μm, less than 0.7 μm, less than 0.5 μm, for example, 0.4 μm.

[0017] Photoresist coating by electrophoretic deposition as claimed in claim 4 has proven to be advantageous in practice. Electrophoretic deposition is known from US Pat. No. 3,738,835 and DE 10 258 094 A1.

[0018] Molecular layer deposition for photoresist coatings has also proven to be useful in the production of diffractive structures of optical elements. Molecular layer deposition is known from US Patent Application Publication No. 2012 / 0121932.

[0019] The advantages of the optical element as claimed in claim 6 correspond to those already mentioned above with regard to the manufacturing method.

[0020] The fabricated optical diffractive structure may be a multi-periodic diffractive structure, a binary diffractive structure, a ternary diffractive structure, or a diffractive structure having four or more steps or structural levels. The number of periods of the multi-periodic diffractive structure fabricated by this fabrication method may be two or more. Alternatively or additionally, the fabricated optical diffractive structure may be a Fresnel lens, a two-dimensional or multi-dimensional grating, or a computer-generated hologram (CGH).

[0021] The advantages of this manufacturing method are particularly evident in the case of an EUV collector as defined in claim 7. The light-diffractive structure can then be used in particular for extraneous light suppression, thereby preventing unwanted extraneous light that is guided along with the EUV used illumination light from entering downstream optical components in the projection exposure apparatus that guide the used light.

[0022] The advantages of this manufacturing method are particularly evident in the case of the diameter of the optical surface as defined in claim 8. The diameter can be greater than 150 mm, greater than 200 mm, greater than 250 mm, greater than 300 mm, greater than 500 mm, greater than 2 m, or greater than 5 m. The upper diameter limit can be 10 m.

[0023] The sidewall steepness according to claim 9 has been found to be advantageous for achieving the desired diffraction results. The sidewall steepness can be greater than 20°, greater than 30°, greater than 40°, greater than 50°, greater than 60°, greater than 70°, greater than 80°, or even greater than 90°, resulting in a diffraction structure whose structure profile narrows toward the structure base. The upper limit of the sidewall steepness can be 110° or 100°. A preferred sidewall steepness is about 90°. Smaller sidewall steepness can be used, particularly for the production of blazed optical grating structures, i.e., blazed diffraction gratings.

[0024] The embodiment of the diffractive structure according to claim 10 has proven to be advantageous for suppressing extraneous light. The extraneous light wavelength to be suppressed can be in the IR wavelength range, for example in the range of 10 μm to 11 μm. The extraneous light wavelength to be suppressed can also be in a wavelength range adjacent to the wavelength of the illumination light used, in particular in the EUV or VUV wavelength range, i.e. in the wavelength range of 5 nm to 200 nm excluding the wavelength of the illumination light used, or in the range of 100 nm to 200 nm.

[0025] The embodiment of the diffractive structure as defined in claim 11 is particularly suited to the requirements for LPP sources (laser produced plasma), in which firstly an extraneous light wavelength range around the laser pump light wavelength and secondly another extraneous light wavelength range around the used light wavelength of the illumination light but excluding exactly this used light wavelength can be suppressed.

[0026] The optical element may in particular be a multi-band grating designed to diffract different wavelength ranges, in particular firstly in the VUV and secondly in the IR.

[0027] Within each external light wavelength band, multiple discrete external light wavelengths can be suppressed, for example, various pulse and main pulse wavelengths in the case of an LPP radiation source, or different EUV and VUV external light wavelengths generated by the plasma.

[0028] The advantages of the illumination system according to claim 12, the projection exposure apparatus according to claim 13, the manufacturing method according to claim 14 and the component according to claim 15 correspond to those already mentioned above with respect to the manufacturing method and the manufactured optical element. The manufactured component can be a microchip, in particular a memory chip.

[0029] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0030] [Figure 1] 1 shows a schematic meridian section of a projection exposure apparatus for EUV projection lithography; [Figure 2] 1 shows a meridian section through a collector of a projection exposure apparatus; [Figure 3] 1 shows a snapshot of the morphology of a meridian cross section of a portion of the (raw) optical surface of a collector during fabrication. [Figure 4] 1 shows a snapshot of the morphology of a meridian cross section of a portion of the (raw) optical surface of a collector during fabrication. [Figure 5] 1 shows a snapshot of the morphology of a meridian cross section of a portion of the (raw) optical surface of a collector during fabrication. [Figure 6] 1 shows a snapshot of the morphology of a meridian cross section of a portion of the (raw) optical surface of a collector during fabrication. [Figure 7] 6 showing a three-level diffractive structure fabricated with a structure having a sidewall steepness of 90°, but showing a three-level diffractive structure with sidewalls having a sidewall steepness of 45° as yet another embodiment of a fabricated optical element having a diffractive structure. [Figure 8] 1 shows a schematic representation of two sidewall portions of a diffractive structure to illustrate the definition of the parameter "sidewall steepness." [Figure 9] 6 and 7, there is shown yet another embodiment of a fabricated optical element having a diffractive structure in the form of a multi-period grating. [Figure 10] 6, 7 and 9 show yet another embodiment of a fabricated optical element having a diffractive structure in the form of a multi-level grating with multiple levels and multiple height differences. DETAILED DESCRIPTION OF THE INVENTION

[0031] First, the general configuration of a microlithography projection exposure apparatus 1 will be described.

[0032] A Cartesian xyz coordinate system is used for the purposes of explanation. In Figure 1, the x-axis extends perpendicular to the plane of the drawing. The y-axis extends to the right. The z-axis extends downward. In connection with the description of the individual components, from Figure 2 onwards, a local Cartesian coordinate system is used, in which the x-axis extends parallel to the x-axis of the global coordinate system shown in Figure 1 and the x- and y-axes each span a principal plane approximating each optical surface.

[0033] 1 shows a schematic representation of a microlithography projection exposure apparatus 1 in a meridional section. In addition to a radiation source 3, the illumination system 2 of the projection exposure apparatus 1 comprises an illumination optical unit 4 for exposing an object field 5 onto an object plane 6. In this case, a reticle 6a arranged in the object field 5 is exposed, said reticle being held by a reticle holder 6b. A projection optical unit 7 serves to image the object field 5 into an image field 8 in an image plane 9. The structures on the reticle are imaged onto a photosensitive layer of a wafer 9a arranged in the region of the image field 8 in the image plane 9, said wafer being held by a wafer holder 9b.

[0034] The reticle holder 6b is driven by a reticle displacement drive 9c, and the wafer holder 9b is driven by a wafer displacement drive 9d, with the two displacement drives 9c and 9d being driven synchronously with each other along the y direction.

[0035] The radiation source 3 is an EUV radiation source having an emitted radiation in the range of 5 nm to 30 nm. It can be a plasma source, such as a GDPP (gas discharge plasma) source or an LPP (laser-produced plasma) source. For example, tin can be excited to form a plasma by a carbon dioxide laser operating at a wavelength of 10.6 μm, i.e., in the infrared range. Synchrotron-based radiation sources can also be used for the radiation source 3. Those skilled in the art can obtain information about such radiation sources, for example, from U.S. Pat. No. 6,859,515. The EUV radiation 10 emerging from the radiation source 3 is focused by a collector 11. The basic design of a corresponding collector is known from U.S. Pat. No. 5,859,515. Downstream of the collector 11, the EUV radiation 10 propagates through an intermediate focal plane 12 before impinging on a field facet mirror 13 having a plurality of field facets 13a. The field facet mirror 13 is arranged in a plane of the illumination optical unit 4 optically conjugate with the object plane 6.

[0036] The EUV radiation 10 is also referred to below as illumination light or imaging light.

[0037] Downstream of the field facet mirror 13, the EUV radiation 10 is reflected by a pupil facet mirror 14 having a plurality of pupil facets 14a. The pupil facet mirror 14 is arranged in a pupil plane of the illumination optical unit 4, which is optically conjugate with the pupil plane of the projection optical unit 7. By means of the pupil facet mirror 14 and an imaging optical assembly in the form of a transfer optical unit 15 having mirrors 16, 17 and 18 shown in beam path order, the field facets 13a of the field facet mirror 13 are imaged onto the object field 5 in a mutually superimposed manner. The final mirror 18 of the transfer optical unit 15 is a grazing incidence mirror (GI mirror).

[0038] 2 shows the collector 11 in more detail, which has a through opening 19 for the pump light to generate the plasma, insofar as the radiation 3 is embodied as an LPP source. The pump light may have a pump light wavelength in the infrared wavelength range, for example at 10.6 μm.

[0039] Collector 11 is an example of an optical element that is manufactured according to a method described in further detail below.

[0040] The collector 11 has an optical surface 20 with a diffractive structure 21, part of which is shown by way of example in Figures 6 and 7 as the result of a manufacturing method. The diffractive structure 21 serves to suppress extraneous light wavelengths different from the used illumination wavelength of the illumination light 10 for which the collector reflection of the collector 11 is designed. The extraneous light wavelengths to be suppressed can firstly be the IR wavelength of the pump laser and secondly the EUV or VUV wavelengths which are additionally generated in addition to the used light wavelength by the generated plasma, for example in the region below the used light wavelength of 13 nm and from the used light wavelength to, for example, the region of 250 nm. The diffractive structure 21 can be specifically designed to suppress two mutually different extraneous light wavelength ranges, for example firstly the IR wavelength range and secondly the VUV wavelength range.

[0041] The optical surface 20 of the collector 11 is concave. A mean surface normal N of the optical surface 20 extends on the axis of rotational symmetry of the optical surface 20. The surface normal N extends parallel to the z-axis of the local xyz coordinate system of the collector 11. Measured along the mean surface normal N, there is a distance A between the lowest point T of the optical surface 20 and the highest point H of the edge of the optical surface 20. When viewed from the z-direction, the optical surface 20 of the collector 11 is round and has a diameter D. The distance-to-diameter ratio A / D is a measure of the curvature of the optical surface 20 of the collector 11. In the case of the collector 11, this ratio A / D is approximately 1 / 4. Depending on the embodiment of the optical element having a diffractive structure to be manufactured, using the collector 11 as an example, the ratio A / D is in the range of 1 / 10 to 1 / 1.

[0042] The diameter D of the optical surface 20 is greater than 100 mm, and in the illustrated exemplary embodiment is approximately 150 mm. Depending on the embodiment of the optical element, for example a collector, the maximum diameter of the optical surface 20 can be in the range of 100 mm to 10 mm.

[0043] A method for manufacturing a collector 11 having an optical surface 20 with a diffractive structure 21 is described below with reference to Figures 3 to 6. Figure 3 shows a snapshot of the manufacturing method. It shows, in a greatly enlarged view, a portion of a raw optical surface 22 that will become the optical surface 20 during the manufacturing method. A substrate 23 of the raw optical surface 22 carries a structurable layer 24 in which the diffractive structure is to be introduced.

[0044] Raw optical element 25 having raw optical surface 22 has a raw distance-to-diameter ratio A / D that deviates by no more than 10% from the distance-to-diameter ratio A / D of finished collector 11. Thus, raw optical surface 22 has a curvature that corresponds to the curvature of finished optical element 11.

[0045] In the snapshot shown in Figure 3, the structurable layer 24 is coated in a structured manner with portions 26, 27 of photoresist. This coating is carried out using an isotropic deposition method. As an isotropic deposition method for coating the raw optical element 25 with photoresist, firstly the method of electrophoretic deposition and secondly the method of molecular layer deposition can alternatively be used.

[0046] During electrophoretic deposition (EPD), colloidal particles are deposited on the electrode, i.e., the raw optical surface 22, under the influence of an electric field. This deposition method is conformal, so that the photoresist portions 26, 27 accurately reproduce the shape of the structurable layer 24 where they are applied. The photoresist portions 26, 27 are applied with a thickness d in the range of 5 μm to 20 μm, for example 6 μm, 8 μm, or 10 μm. The thickness variation of the thickness d across the xy footprint of the raw optical surface 22 is less than 2 μm, in particular less than 1 μm, less than 0.5 μm, and values ​​of 0.4 μm can be achieved. By way of example, the thickness of the applied photoresist portions 26, 27 may vary by 0.4 μm or less across the raw optical surface 22 of the collector 11, for example 7.8 μm to 8.2 μm.

[0047] Aqueous suspensions can be used as EPD photoresists, and the solids in the suspension are called micelles. These micelles can consist of an acrylic copolymer shell and are stabilized by a surface charge of ionizable amino groups. Those skilled in the art can find details regarding electrophoretic deposition in U.S. Pat. No. 3,738,835, DE-A-19 258 094, and EP-A-0 176 356.

[0048] The photoresist portions 26, 27 are deposited in deposition cells. An electric potential is applied to the conductive workpiece, i.e., the optical blank 25, the polarity of which attracts charged cells of the photoresist, which coalesce to form a uniform film on the structurable layer 24. The layer thickness d of the photoresist portions 26, 27 and the distribution of the portions 26, 27 can vary and be correspondingly controlled by the applied deposition voltage, deposition temperature, and deposition dwell time.

[0049] 4 shows the situation after the development of the photoresist, i.e., after the etching removal of the photoresist portions 26, 27. Two levels have been formed in the structurable layer: an upper level N1 where the photoresist portions 26, 27 were located, and a deeper level N2 where the structurable layer 24 is exposed, i.e., not covered by photoresist. The sidewall steepness of the structure sidewall F between the upper level N1 and the deeper level N2 is, to a good approximation, 90°. Thus, the sidewall F is perpendicular to the surfaces of the first upper level N1 and the second lower level N2.

[0050] FIG. 8 illustrates the definition of the parameter "sidewall steepness angle." Two sidewalls F1 and F2 with different structures are shown as examples. Sidewall F1, with a sidewall steepness of 90°, forms an angle of 90° with the horizontal line (corresponding to the xy plane in FIGS. 3 to 7). Sidewall F2, with a sidewall steepness of 10°, forms an angle of approximately 10° with the horizontal line H.

[0051] 5 shows the situation after yet another second coating step, in which the structurable layer 24 of the raw optical surface 22 is once again coated with portions 28, 29 of photoresist. Due to the coating by electrophoretic deposition, the shape of the photoresist portions 28, 29 exactly follows the structure already introduced in the structurable layer 24. The photoresist portions 26, 27 therefore present two resist levels R1 (higher level) and R2 (deeper level), the height difference ΔR between which is exactly equal to the height difference ΔN between levels N1 and N2 of the structurable layer 24 during the manufacturing step shown in FIG.

[0052] Even in the region of the sidewalls F of the structurable layer 24, a thickness d of photoresist is present, measured in the y direction, after the coating step shown in Figure 5. This ensures that the sidewalls F of the structurable layer 24 are covered with photoresist, if desired.

[0053] 6 shows the finished optical surface 20 with respect to the diffractive structure to be produced after development of the raw optical surface 22 with photoresist portions 26, 27. The diffractive structure is embodied as a three-part structure having three levels N1, N2, and N3.

[0054] The deepest level N3 is where the structurable layer 24 was able to be etched due to gaps between the photoresist portions 28, 29. The sidewalls between levels N2 and N3 also have a sidewall steepness that is to the best of approximation 90°.

[0055] In the three-part structure of the diffractive structure 20, the height difference ΔN 1 / 2 , ΔN 2 / 3 The desired extraneous light suppression can be achieved depending on the configuration of the levels N1, N2, and N3 and the size of the levels N1, N2, and N3 in the xy plane.

[0056] In an alternative molecular layer deposition method, first photoresist portions 26, 27 and second photoresist portions 28, 29 are deposited by molecular layer deposition rather than electrophoretic deposition as described above. Such a method is described, for example, in U.S. Patent Application Publication No. 2012 / 0121932. The photoresist is deposited by two or more self-limiting surface reactions, which are periodically performed, resulting in the deposition of molecular fragments. A multi-component photoresist system that forms a molecular glass can be used as the photoresist. One of these components, a photoacid (photoacid generator, PAG), releases an acid upon irradiation with an appropriate wavelength in multiple steps, which then catalyzes a reaction between other components of the photoresist system upon brief heating of the system (post-exposure bake, PEB). Because the multi-component reactions are initiated by the irradiation photons, this process is called chemical amplification.

[0057] Alternatively, photoresist systems based on coumarin derivatives that react with themselves can be used as photoresists; these derivatives undergo a [2+2] cycloaddition reaction upon UV exposure at wavelengths above 300 nm. As a result, molecular dimers, chains, or networks can form in the molecules of the photoresist system, depending on the number of functional groups. 1,3-dibenzyl-5-tert-butylcoumarin ester and 3,5-di-tert-butylbenzylcoumarin ester are preferred, as they form transparent, amorphous films. After exposure, the monomer in the unexposed regions can be evaporated in a high-vacuum system, resulting in photoresist properties, albeit those associated with "dry" photolithography.

[0058] After removal of the photoresist portions, the produced diffractive structure 21 can be provided with a sealing or protective layer. This can be done by atomic layer deposition (ALD), for example, as known from U.S. Pat. No. 9,640,291 and U.S. Patent Application Publication No. 2016 / 0086681. In particular, a molybdenum-silicon bilayer can serve as a protective layer. Details of such stacks are known from the prior art.

[0059] The method steps "Developing the photoresist" and "Removing photoresist residues" are known from US Pat. No. 6,229,999.

[0060] Figure 7 shows, in a view similar to Figure 6, yet another embodiment of a diffractive structure 30 that can be manufactured instead of the diffractive structure 21 or instead of the diffractive structures also described below during the manufacture of the optical element, i.e. in particular the collector 11. Components and features that correspond to those already described above with respect to the embodiment shown in Figures 2 to 6, in particular the embodiment shown in Figures 3 to 6, have the same reference numerals and will not be described in detail again.

[0061] The diffractive structure 30 also has three structure levels N1, N2 and N3. The sidewalls F, firstly between levels N1 and N2 and secondly between levels N2 and N3, have sidewall steepness in the range of 40° or 45°.

[0062] Diffractive structures with sidewalls F whose sidewall steepness is in particular in the range of 10° to 80°, for example in the range of 30° to 60°, can be produced in particular using greyscale lithography. Those skilled in the art can find information on corresponding manufacturing techniques for sidewalls F with such sidewall steepness in A. Grushina (Advanced Optics Techn. 2019; 8 (3 to 4): 163-169), T. Weichelt et al. (Optics Express, Volume 25, No. 18, pp. 20983 to 20992, 2017), T. Weichelt et al. (Journal of Optics 18 (2016) 125401), C. Stilson et al. (Proceedings of SPIE 8973: Micromachining and Microfabrication Process Technology XIX, No. 8973 (March 2014)), K. Reimer et al. (Proceedings SPIE Vol. 3008, pp. 279 to 288, 1997), T. J. Suleski (Applied Optics, Volume 34, (Applied Optics, Volume 34, No. 32, 7518 to 7526, 1995), and in the technical articles by DC O'Shea et al. (Applied Optics, Volume 34, No. 32, 7518 to 7526, 1995), as well as in the references given in the above articles.

[0063] Blazed diffractive structures can be fabricated with a particular desired sidewall steepness.

[0064] 9 and 10, two embodiments of diffractive structures 31, 32 or optical gratings that can be produced instead of the diffractive structures described above during the production of the optical element, i.e. in particular the collector 11. Components and features that correspond to those already described above with respect to the embodiments shown in Figures 2 to 8, in particular those shown in Figures 6 and 7, have the same reference numerals and will not be described in detail again.

[0065] The diffractive structure 31 shown in FIG. 9 is embodied as a multi-period diffraction grating having periods T1 and T2. It can be stated that: T1 = 7T2, where the ratio T1 / T2 can be, for example, in the range of 1.1:1 to 100:1, or outside this range. Thus, the period T2 occurs a total of seven times within the period T1, with the positive structure PS of the period T1 extending over a total of 4.5 grating periods T2, and the negative structure NS of the grating period T1 extending over the remaining 2.5 grating periods T2. Thus, the duty cycle of the grating with period T1 is 9 / 5. The height difference ΔN of the grating with period T1 is T1 is the height difference ΔN of the grating with period T2 T2 It is about five times the size of

[0066] Thus, the duty cycle of the grating with period T2 is 1:1, so that in that respect each positive structure has the same extent in the grating extension direction along the y direction as one of the negative structures of the grating with period T2.

[0067] The difference in height ΔN is due to the grating periods T1 and T2. T1 , ΔN T2 By this and also by the duty cycles of the two gratings with grating periods T1 and T2, the extraneous light suppression characteristics of the diffractive structure 31 can be precisely defined in advance.

[0068] The diffractive structure 32 shown in FIG. 10 is embodied as a multi-stage diffractive grating having a grating period T. Generally, the diffractive structure 32 has seven different diffractive levels N1 to N7 in one period, and the structural height of level Ni+1 is smaller than the structural height of level Ni. The order of these structural levels in period T is N1, N2, N3, N4, N6, N5, N7, N5, N6, N4, N3, and N2. Other numbers of structural levels and other orders are possible depending on the embodiment of the multi-period grating of the diffractive structure 32.

[0069] Furthermore, the diffractive structure 32 has two different height differences ΔN i / j and ΔN k / lIn the exemplary embodiment of FIG. 10, the larger height difference ΔN between levels N1 / N2, N2 / N3, N4 / N6, and N5 / N7 i / j is the difference in elevation ΔN between levels N3 / N4 and N6 / N5 k / l It is about twice the size of

[0070] Around the deepest level N7, the level arrangement of the diffractive structure 32 is mirror-symmetric with respect to a plane 33 parallel to the xz plane.

[0071] The external light suppression parameter of the diffractive structure 32 is determined by the relative structural heights of the levels N1 to N7, the structural height order of the levels N1 to N7, and the height difference ΔN i / j and ΔN k / l The temperature can also be specified in detail in advance by

[0072] Depending on the embodiment of the diffractive structure 32, other absolute numbers of height differences and some other number of different height differences are possible.

[0073] For the lithographic production of microstructured or nanostructured components, in particular semiconductor components, e.g. microchips, the projection exposure apparatus 1 is used to image at least a part of a reticle in the object field 5 onto an area of ​​a photosensitive layer on a wafer in the image field 8. In this case, the photoresist is exposed in a structured manner and subsequently developed. Depending on the embodiment of the projection exposure apparatus 1 as a scanner or as a stepper, the reticle and the wafer are moved synchronously in time in the y direction, either continuously in a scanner operation or stepwise in a stepper operation.

Claims

1. A method for manufacturing an optical element (11) having an optical surface (20) with a diffractive structure (21; 30; 31; 32) that is a multi-band grating that suppresses an external light wavelength range that includes at least the IR wavelength range and the EUV or VUV wavelength range excluding illumination light (10), comprising: The optical surface (20) is the distance A between the deepest point (T) and the highest point (H) on the optical surface (20) measured along the mean surface normal (N) of the optical surface (20); The maximum diameter D of the optical surface (20) In the method, the curved surface has a distance to diameter ratio A / D of greater than 1 / 10, providing a raw optical element (25) having a raw optical surface (22) on which said diffractive structures (21; 30; 31; 32) are provided; coating said raw optical surface (22) with photoresist (26, 27; 28, 29) using an isotropic deposition method; structuring and exposing the photoresist; developing the photoresist (26, 27; 28, 29); Including, The steps of coating the raw optical surface with photoresist using the isotropic deposition method and developing the photoresist are repeated sequentially during the manufacturing process.

2. 2. A method according to claim 1, characterized in that during coating, the photoresist (26, 27; 28, 29) is applied with a thickness D ranging from 5 μm to 20 μm.

3. 3. The method according to claim 1 or 2, characterized by a thickness variation of the applied photoresist (26, 27; 28, 29) that is less than 20% of the maximum thickness of the applied photoresist (26, 27; 28, 29).

4. A method according to any one of claims 1 to 3, characterized in that the coating is carried out by electrophoretic deposition.

5. The method according to any one of claims 1 to 3, characterized in that the coating is performed by molecular layer deposition.

6. An optical element (11) manufactured by the method according to any one of claims 1 to 5.

7. 7. An optical element according to claim 6, embodied as an EUV collector for use in a projection exposure apparatus.

8. 8. An optical element according to claim 6 or 7, characterized by a diameter of the optical surface (20) exceeding 100 mm.

9. Optical element according to any one of claims 6 to 8, characterized in that the diffractive structure (21; 30; 31; 32) has a sidewall steepness of more than 10°.

10. 10. The optical element according to claim 6, characterized in that the diffractive structure (21; 30; 31; 32) is configured such that, when the illumination light (10) is incident on the optical element (11), at least one extraneous light wavelength different from the illumination light wavelength of the illumination light (10) for which the optical element (11) is designed is suppressed by diffraction.

11. 11. The optical element according to claim 10, characterized in that the diffractive structure (21) is configured such that when the illumination light (10) is incident on the optical element (11), two mutually different extraneous light wavelength ranges are suppressed.

12. An illumination system (2) comprising an optical element according to any one of claims 6 to 11 and comprising an EUV radiation source (3).

13. 13. A projection exposure apparatus for EUV projection lithography, comprising: an illumination system according to claim 12; an illumination optical unit (4) for transmitting illumination light (10) from a radiation source (3) to an object field (5) in which a reticle having a structure to be imaged can be arranged; and a projection optical unit (7) for imaging the object field (5) into an image field (8).

14. 1. A method for manufacturing a microstructured or nanostructured component, comprising: providing a substrate (9a) on which a layer of photosensitive material is at least partially applied; Providing a reticle (6a) having a structure to be imaged; projecting at least a part of the reticle (6a) onto an area of ​​the photosensitive layer of the substrate (9a) using a projection exposure apparatus according to claim 13; A method comprising:

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