Intermediate product for producing optical element of projection exposure apparatus, optical element of projection exposure apparatus, method for producing intermediate product, and method for producing optical element

Abstract

An intermediate product for producing an optical element for a projection exposure apparatus (1), comprising a substrate (20) for specifying a basic topography of an optical surface, in which a plurality of etchable layers comprising a layer (22i) to be structured and a contrast layer (23i) are applied to the substrate (20), in which the layer (22i) to be structured and the contrast layer (23i) have different chemical properties, the removal of the contrast layer (23i) can be detected in situ.

Description

[0001] This patent application claims the priority of German patent application DE 10 2022 208 658.9, the content of which is incorporated herein by reference. Technical Field

[0002] The present invention relates to an intermediate product for producing an optical element for a projection exposure apparatus, in particular for producing a reflector for a projection exposure apparatus, in particular an EUV projection exposure apparatus. The present invention also relates to an optical element for a projection exposure apparatus, in particular a reflector. Furthermore, the present invention relates to a production method for an intermediate product for producing an optical element for a projection exposure apparatus. Furthermore, the present invention relates to a method for producing an optical element for a projection exposure apparatus. Finally, the present invention relates to an apparatus for producing an optical element for a projection exposure apparatus. Background Art

[0003] Precise specification of the surface topography of optical elements, in particular mirrors, of a projection exposure apparatus is important for its production. It is difficult to precisely produce optical elements with a precisely specified surface topography. Summary of the invention

[0004] The problem addressed by the invention is to improve intermediate products for producing optical elements in projection exposure apparatuses and optical elements produced therefrom.

[0005] This problem is solved by an intermediate product as claimed in claim 1 and an optical element produced therefrom.

[0006] One aspect of the invention comprises applying a plurality of structurable layers, in particular etchable layers, to a substrate, wherein at least a subset of these layers serves as a contrast layer. This is understood to mean that the removal of the contrast layer is detectable, in particular detectable in situ.

[0007] As a result, the structuring of the layer to be structured can be monitored during the structuring process, in particular without interrupting the structuring process. In particular, it is not necessary to measure the intermediate product by means of a separate measuring method. This significantly improves the production process of the intermediate product and the optical element that can be produced therefrom.

[0008] The substrate to which the structurable layer is applied may have a planar surface, in particular a substantially planar surface, in particular a completely planar surface, or a curved surface, in particular a convex or concave surface. In particular, the substrate may have a surface topography that can be described by a continuously differentiable function. However, in principle, a surface topography with kinks and / or jump discontinuities is also possible.

[0009] According to one aspect of the invention, the contrast layer may in particular also comprise an etchable material. In particular, it may consist of an etchable material.

[0010] A material is considered etchable if physical and / or chemical removal of the material can be achieved by wet and dry etching methods. To produce the topography, the etching rate of the material in the process can in particular be higher or at least not significantly lower than the etching rate of the etching mask used here (usually made of oxide, nitride or metal (=hard mask) or polymer (=photomask)).

[0011] According to a further aspect, at least 90%, in particular at least 95%, of the different layers, in particular the layer to be structured and the comparison layer, can consist of materials whose etching rates, in particular in a given etching method, deviate from one another by no more than 10%.

[0012] This makes it possible for the layer to be structured and the comparison layer to be structured in essentially the same way, in particular if they are subjected to the same structuring method.

[0013] In particular, the etching method may be a dry etching method, in particular ion etching (RIE, reactive ion etching) or DRIE (deep reactive ion etching) or ion beam etching, in particular reactive ion beam etching (RIBE).

[0014] For example, hydrofluorocarbon CxHyFz (y, x, z are integers including 0) can be used as a process gas in a dry etching method for etching silicon or silicon-containing compounds (SiOx, SiNx).

[0015] Possible additives to the gas mixture in this case are oxygen, nitrogen and argon.

[0016] Typically, accelerating voltages of 30 V to 300 V are conventional in RIE, and 0.5 kV to 2 kV are also conventional in ion beam etching (RIBE).

[0017] What can be utilized here is the fact that a parameter window can be found in each case in which the etching rates of the aforementioned materials do not differ significantly.

[0018] According to another aspect, the different layers, in particular the layer to be structured and the contrast layer, can consist of materials whose densities differ from one another by no more than 10%, in particular by no more than 5%, in particular by no more than 3%, in particular by no more than 2%, in particular by no more than 1%.

[0019] According to another aspect, the layers can have a correspondingly similar roughening behavior.

[0020] According to a further aspect, the contrast layer and the layer to be structured can have starting materials of the same chemical nature, in particular the same chemical element or the same compound, wherein the starting material of the contrast layer is modified by doping or ion implantation.

[0021] In particular, the contrast layer and the layer to be structured can consist of the same starting material, wherein the starting material of the contrast layer is modified, in particular by doping or ion implantation.

[0022] The material of the contrast layer can contain, in particular, at least one further chemical element or one or more further chemical compounds.

[0023] Preferably, all contrast layers and / or layers to be structured are made of corresponding starting materials of the same chemical nature. In particular, they can consist of the same starting material with a specified modification.

[0024] According to another aspect of the invention, the contrast layer may have a thickness, in particular a maximum thickness, of not more than 10 nm, in particular not more than 5 nm, in particular not more than 3 nm, in particular not more than 2 nm, in particular not more than 1 nm, in particular not more than 0.5 nm.

[0025] A lower thickness of the contrast layer may result in a higher precision in the production of specific surface topography.

[0026] According to another aspect of the invention, the layer to be structured may have a thickness in the range of 10 nm to 50 μm. The thickness of the layer to be structured may in particular have at least 20 nm, in particular at least 30 nm, in particular at least 50 nm, in particular at least 100 nm. The thickness of the layer to be structured may in particular be not more than 30 μm, in particular not more than 20 μm, in particular not more than 10 μm, in particular not more than 5 μm, in particular not more than 3 μm, in particular not more than 2 μm, in particular not more than 1 μm.

[0027] The ratio of the thickness of the contrast layer to the thickness of the layer to be structured can in particular be between 1:10 and 4 In particular, the ratio is at least 1:10. 4 , especially at least 1:10 3 .

[0028] In particular, the ratio is not more than 1:1, in particular not more than 1:2, in particular not more than 1:5, in particular not more than 1:10, in particular not more than 1:20; in particular not more than 1:30, in particular not more than 1:50, in particular not more than 1:100, in particular not more than 1:200, in particular not more than 1:300, in particular not more than 1:500, in particular not more than 1:1000.

[0029] According to another aspect of the invention, the intermediate product can include a plurality of contrast layers, which form intermediate layers in the layer to be structured. In this case, the contrast layer can also form an intermediate layer between the substrate and the layer to be structured.

[0030] The number of contrast layers may be at least 2, in particular at least 3, in particular at least 5, in particular at least 10, in particular at least 20, in particular at least 30, in particular at least 50, in particular at least 100.

[0031] A greater number of contrast layers allows for improved monitoring of the structuring process. A smaller number of contrast layers facilitates the production of intermediate products.

[0032] According to another aspect of the invention, the intermediate product may comprise a plurality of contrast layers, wherein at least two of the contrast layers have different chemical compositions and / or different modifications. In particular, at least two contrast layers may have different doping or be implanted with different ions.

[0033] In particular, it is advantageous if at least two contrast layers are formed in such a way that they can be unambiguously verified by mass spectrometric methods, in particular by residual gas analysis.

[0034] Thus, one or more of the contrast layers can take the form of special signal layers which can be used in particular to control the structuring process.

[0035] All contrast layers can also be made of the same material, in particular have the same chemical composition and / or the same modification.

[0036] It can also be provided that all contrast layers have a different chemical composition and / or a different modification.

[0037] It can also be provided that the intermediate product comprises a single contrast layer which differs from all other layers, in particular from all other contrast layers, in its chemical composition and / or modification.

[0038] This unique contrast layer can be used to trigger special signals, especially stop signals.

[0039] According to another aspect of the invention, the intermediate product may comprise a plurality of contrast layers with different distances between them. In this case, it is possible that only a subset of the contrast layers have different distances between them. It is also possible that all contrast layers have different distances between them, in particular distances that are different in each case in pairs. It is also possible that a subset of the contrast layers, in particular all contrast layers, have the same distances between them.

[0040] In particular, provision can be made for the distance between the contrast layers to increase with increasing distance from the substrate, in particular to grow monotonically, in particular to grow strictly monotonically.

[0041] This may be advantageous for controlling the structuring process. In particular, it has been recognised that tighter and tighter control of the structuring process may be advantageous as the structuring process progresses.

[0042] According to another aspect of the invention, one or more subsets of contrast layers can form a special sequence. To this end, they can have a predetermined sequence of their thickness and / or the distance between them and / or the chemical composition. Such a sequence can be used as a structured control signal for controlling a production process, in particular for controlling an intermediate product.

[0043] According to a further aspect of the invention, one or more contrast layers and / or one or more layers to be structured have a thickness which varies within its range.

[0044] In this case, the thickness can in each case be measured locally perpendicularly to the surface, in particular perpendicularly to the front side or back side of the respective layer.

[0045] In particular, it can be provided that exactly one of the contrast layer and / or the layer to be structured is formed with a thickness which varies within its extent.

[0046] It can also be provided that all contrast layers and / or all layers to be structured have thicknesses which vary within their scope.

[0047] All contrast layers and / or all layers to be structured can also have a constant thickness across their extent.

[0048] According to another aspect of the invention, the intermediate product may comprise a plurality of contrasting layers, wherein at least two of the contrasting layers have a distance between them that varies within a range.

[0049] According to another aspect of the invention, the intermediate product may include a plurality of layers to be structured, wherein at least two of the layers to be structured have a distance between them that varies within their range.

[0050] In particular, one or more contrast layers and / or one or more layers to be structured may be provided with a thickness gradient.

[0051] This can improve, in particular simplify, the production of a defined surface topography, in particular the production of an optical component having a defined surface topography. This can be advantageous, in particular in the production of optical elements having free-form surfaces.

[0052] According to another aspect of the invention, an optical element for a projection exposure apparatus, in particular an EUV projection exposure apparatus, can be produced from the above-described intermediate product.

[0053] The optical element may in particular comprise a radiation reflecting layer, in particular an EUV radiation reflecting layer.In particular, a double stack, in particular a molybdenum-silicon double stack, may be used as the radiation reflecting layer.

[0054] In particular, the optical element can be a mirror, in particular a mirror with a grating structure. The grating structure can be used as a spectral filter, in particular for suppressing unwanted wavelengths. In particular, the grating can be used to suppress infrared radiation and / or in the case of an EUV mirror for suppressing DUV radiation.

[0055] In particular, the reflector can be a collector mirror, in particular a collector reflector of a radiation source module of a projection exposure apparatus, a reflector of an illumination optical unit of a projection exposure apparatus, in particular a facet reflector, in particular a single facet, or a reflector of a projection optical unit of a projection exposure apparatus.

[0056] The reflector may have a total reflection area of ​​more than 100 square centimeters, in particular more than 200 square centimeters, in particular more than 300 square centimeters, in particular more than 500 square centimeters, in particular more than 1000 square centimeters, in particular more than 2000 square centimeters, in particular more than 3000 square centimeters, in particular more than 5000 square centimeters, in particular more than 10 000 square centimeters. Typically, the total reflection area of ​​the reflector is less than 10 square meters. However, this should not be understood as restrictive.

[0057] The optical element may also have a smaller total reflective area.

[0058] A further problem addressed by the present invention is to improve the method for producing an intermediate product according to the preceding description and the method for producing an optical element of a projection exposure apparatus according to the preceding description.

[0059] These problems are solved by a method comprising the following steps:

[0060] - providing a substrate for specifying the basic topography of the optical surface,

[0061] - applying a plurality of etchable layers to the substrate, wherein the layers comprise at least one layer to be structured and at least one contrast layer,

[0062] - wherein the layer to be structured and the comparison layer have different chemical properties, making it possible to detect the removal of the comparison layer in situ.

[0063] The method for producing an optical element further comprises the following steps:

[0064] - structured intermediate products, and

[0065] - In situ monitoring of structuring processes.

[0066] The method according to the invention enables structuring of intermediate products for the production of EUV mirrors with sufficiently precise etch rate control while placing high demands on profile fidelity.

[0067] In particular, an etching method, in particular a dry etching method, in particular ion etching, in particular reactive ion etching or reactive ion beam etching, is provided for structuring an intermediate product.

[0068] In particular, mass spectrometry methods, especially residual gas analysis, can be used to monitor structuring processes in situ.

[0069] Radiation reflecting coatings, in particular EUV radiation reflecting coatings, may be applied to the structured intermediate product.

[0070] By providing a contrast layer, the application of which can be reliably verified in situ, the progress of the material removal can be precisely monitored spatially and / or temporally. The interruption of the structuring process, which was previously required in order to determine the step depth that has been etched, can be omitted.

[0071] Since there is no need to interrupt the structuring process to monitor the progress of the structuring process, the overall process duration can be significantly reduced.

[0072] Since there is no need to remove intermediate products from the vacuum chamber for control measurements, the risk of contamination is reduced.

[0073] Furthermore, there is no risk that the mirror surface is modified by contact with the atmosphere, which could in particular lead to undesired changes in the etching rate.

[0074] Changes in the process chamber are also reliably prevented.

[0075] In particular, the progress of the structuring of the intermediate product can be monitored accurately and reliably during the structuring process, ie in situ.

[0076] Advantageously, the structuring of the intermediate product can be controlled based on the monitoring of the structuring process. For this purpose, a feedback loop can be provided. Thus, the structuring of the intermediate product can be regulated (closed loop method).

[0077] In particular, varying etching rates due to wear or long process durations can be detected via the feedback signal. This can be compensated by increasing the power in the etching process, for example based on an evaluation of the peak distance in the residual gas analysis.

[0078] According to one aspect of the invention, provision can be made for an in-situ analysis of the removed layer to monitor the structuring process, wherein the evaluation of this analysis is used in particular as a control signal for a further structuring process.

[0079] In situ analysis can be used in particular to determine the chemical signature, in particular the chemical fingerprint, of the at least partially removed layer.

[0080] In the structuring of the intermediate product, different contrast layers, in particular contrast layers with different chemical compositions and / or with different modifications and / or sequences of contrast layers, in particular contrast layers with different thicknesses and / or different distances between them and / or different numbers of contrast layers, can be used as signal transmitters, in particular for different control signals.

[0081] The structuring of an intermediate product for producing an optical element for a projection exposure apparatus can take a long time, in particular hours or even days, in particular in the case of optical elements with a large total reflection area. By means of a targeted arrangement and / or formation of the contrast layer, the structuring process can in this case be monitored very precisely without interrupting the structuring process in the process, in particular without removing the intermediate product, in particular an intermediate product which may have already been partially structured, from a vacuum atmosphere provided for structuring, in particular from a vacuum chamber provided for this purpose, in particular from an at least partially evacuated vacuum chamber provided for this purpose.

[0082] According to another aspect of the invention, a method for maintaining roughness, in particular a smoothing method, such as a sputtering method, in particular a magnetron sputtering method (MSD, magnetron sputtering deposition), a physical or chemical vapor deposition method (PVD, CVD, in particular plasma enhanced CVD, PECVD), an atomic layer deposition method (ALD method), a pulsed laser deposition method (PLD method), an ion beam sputtering method or an electron beam evaporation method can be provided for applying the layer to be structured and / or for applying a contrast layer.

[0083] Such an application method enables a very precise application of the layer, in particular with a predetermined thickness, in particular with a predetermined thickness profile.

[0084] According to another aspect of the invention, a method for applying a layer is provided which may comprise only the addition step of maintaining the roughness.

[0085] A further problem addressed by the invention is that of improving an apparatus for producing optical elements for a projection exposure apparatus.

[0086] This problem is solved by a device that has the following features:

[0087] a vacuum chamber for receiving intermediate products for producing optical elements for a projection exposure apparatus,

[0088] - a device for structuring the intermediate product in a vacuum chamber,

[0089] - structured devices for in-situ monitoring of intermediate products,

[0090] wherein the device for monitoring the structuring of the intermediate product is coupled in a data transmission manner to the device for structuring the intermediate product in the vacuum chamber.

[0091] In particular, the intermediate product is an intermediate product according to the previous description.

[0092] In particular, the device comprises control means for controlling the means for structuring the intermediate product.

[0093] In particular, a feedback loop can be provided at the device for monitoring the structuring and at the device for structuring the intermediate product.

[0094] Detection by means of residual gas analysis can be carried out in particular by means of one or more mass spectrometers. The use of a plurality of detectors / measuring devices can increase the precision, in particular improve the signal-to-noise ratio.

[0095] The mass spectrometer is preferably selected in such a way that masses with higher atomic numbers can also be detected. This can be matched to the additive material in the signal layer.

[0096] In particular, multiple mass spectrometers may be distributed in the chamber in such a way that the spatial distribution of the etch rate can be determined (in a manner similar to triangulation) by appropriate evaluation of the measurement data at a specific chamber pressure. This may be advantageous, for example, when calibrating or determining tool functionality.

[0097] The mass spectrometer may be located in the backscatter region of the etched material.

[0098] The mass spectrometer may not be located directly in the process chamber (the mass spectrometer operating pressure is usually ideally 10 -8 mbar to 10 -6 mbar, max 10 -4 mbar), especially at higher chamber pressures in etching processes (especially at 10 -4 mbar to 5.10 -4 mbar range). This problem is solved by positioning in a differentially pumped area (secondary chamber) which is connected to the main process chamber only via a pinhole (= gas flow restriction). This area can then be at a lower pressure and the detected mass ratio remains almost the same.

[0099] Furthermore, the invention relates to a collector, an illumination optical unit, an illumination system, a radiation source module and a projection exposure apparatus having optical components according to the preceding description, and also to a method for producing a nanostructured component and a component produced according to the method.

[0100] In principle, one or more etch stop layers can also be specified.

[0101] The etch stop layers can differ significantly from the contrast layer. In particular, they can be made of a material that differs significantly from the structured layer. In particular, they can have a different etching rate, in particular a significantly lower etching rate, than the structured layer. For details, reference should be made to German patent application DE 10 2020 207807.9. The combination of contrast layer and etch stop layer can also bring advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0102] Further details and advantages of the present invention will become apparent from the description of exemplary embodiments with reference to the accompanying drawings, in which:

[0103] Figure 1 schematically shows a meridional section through a projection exposure apparatus for EUV projection lithography,

[0104] Figure 2 schematically shows a detail from a cross section through an intermediate product for producing an optical element,

[0105] Figure 3 A sequence of process steps from a process chain for producing an optical element is schematically shown,

[0106] Figure 4 schematically shows a cross section through an intermediate product for producing an optical component with a curved reflective surface,

[0107] Figure 5 schematically shows a detail of a cross section through an intermediate product for producing an optical element, and

[0108] Figure 6 Schematically shows the structure of the Figure 5 details. DETAILED DESCRIPTION

[0109] Firstly, the general construction of a microlithography projection exposure apparatus 1 will be described.

[0110] Figure 1 A meridional section through a microlithography projection exposure apparatus 1 is schematically shown. The illumination system 2 of the projection exposure apparatus 1 has, in addition to a radiation source 3, an illumination optical unit 4 for exposing an object field 5 in an object plane 6. In this case, a reticle (not shown in the figure) arranged in the object field 5 and held by a reticle holder (also not shown) is exposed. The 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 (also not shown in the figure) which is arranged in the image plane 9 in the region of the image field 8 and held by a wafer holder (also not shown).

[0111] The radiation source 3 is an EUV radiation source having radiation used in an emission range between 5 nm and 30 nm. This can be a plasma source, such as a GDPP (gas discharge produced 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. Information about such radiation sources can be found by a person skilled in the art, for example, in US 6,859,515 B2. The EUV radiation 10 emitted from the radiation source 3 is focused by a collector 11. A corresponding collector is known from EP 1 225 481 A. Downstream of the collector 11, the EUV radiation 10 propagates through an intermediate focal plane 12 before being incident 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, which is optically conjugate relative to the object plane 6.

[0112] EUV radiation 10 is also referred to below as illumination light or imaging light.

[0113] 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 respect to a pupil plane of the projection optical unit 7. With the aid 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 assigned in the order of the beam paths, the individual field facets (also called subfields or individual mirror groups) of the field facet mirror 13 are imaged into the object field 5. The last mirror 18 of the transfer optical unit 15 is a mirror for grazing incidence ("grazing incidence mirror").

[0114] With the aid of the projection exposure apparatus 1, at least a portion of the reticle in the object field 5 is imaged onto a region of a photosensitive layer on a wafer in the image field 8 for the lithographic production of microstructured or nanostructured components, in particular semiconductor components, such as microchips. Depending on the embodiment of the projection exposure apparatus 1 as a scanner or a stepper, the reticle and the wafer are moved in a time-synchronized manner in the y-direction, continuously in scanner operation or stepwise in stepper operation.

[0115] References below Figures 2 to 5 A method for producing an optical element for a projection exposure apparatus 1 and intermediate products in the production of this optical element are described.

[0116] The optical element may in particular be a reflector, in particular a reflector of the illumination optical unit 4 or of the projection optical unit 7. In particular, it may be a reflector of the collector 11. It may also be a spectral filter, in particular a filter for suppressing infrared radiation (IR radiation). In particular, it is an EUV reflector with an IR suppression effect. For further details of such optical elements, reference is made by way of example to PCT / EP 2019 / 082 407, to which PCT / EP 2019 / 082 407 is hereby cited.

[0117] First, a substrate 20 is provided in a providing step 19. The substrate 20 is used to specify the basic topography of the optical element. In particular, it can have a non-planar, i.e. curved surface. In particular, it can have a convex or concave surface. The substrate can have an aspherical, in particular ellipsoidal, or parabolic basic topography.

[0118] In the application step 21 , the layer 22 to be structured is applied i (i≥1) and comparison layer 23 i A sequence of (i≥1) is applied to the substrate 20 .

[0119] The layer 22 to be structured i and contrast layer 23 i It can be applied in particular by means of a deposition method, in particular by means of a sputtering method, in particular by means of a magnetron sputtering method (MSD, magnetron sputter deposition) or by means of a vapor deposition method (PVD, CVD, PECVD) or an atomic layer deposition method (ALD) or a pulsed laser deposition (PLD) method, an ion beam sputtering method or an electron beam evaporation method.

[0120] The layer 22 to be structured i With thickness D i Application. Layer thickness D i can vary on the surface of the substrate 20, D i =D i (s); Here, s represents the position on the surface of the substrate 20. The etching layer 22 i is applied to the substrate 20, in particular with a layer thickness distribution D according to a specified iv (s) layer thickness D i (s).

[0121] Layer thickness D i (s), in particular in the region of the entire surface of the substrate 20, deviates from the specified layer thickness D iv (s) not more than 1%.

[0122] The layer 22 to be structured iThey have a smooth surface. Their surface roughness is in particular 0.15 nm rms. The present description relates in particular to the range of high spatial frequencies, in particular at least 1 / μm.

[0123] The layer 22 to be structured i In particular, the thickness D is several μm. i In particular, the layer 22 to be structured i Thickness D i It can be in the range of 0.1 μm to 12 μm.

[0124] The total thickness of the coating of the substrate 20, in particular all layers 22 to be structured i and contrast layer 23 i The sum of the thicknesses of , in particular, does not exceed 100 μm, in particular does not exceed 50 μm, in particular does not exceed 30 μm, 20 μm, in particular does not exceed 10 μm. These specifications should not be understood as restrictive.

[0125] The layer 22 to be structured i For example, it can be made of crystalline amorphous silicon, SiO2, Si3N4 or other silicon-based compounds.

[0126] Their thickness D i Set directly during coating. Thickness D i In particular, it can be set with an accuracy of better than 1%, in particular better than 0.5%, in particular better than 0.3%, in particular better than 0.2%.

[0127] Contrast layer 23 i Preferably, the layer 22 to be structured i Comparative layer 23 i It can be made in particular of a material which has a comparable etching rate and / or a comparable density and / or a comparable roughening behavior in the same etching process. In this case, comparable properties are understood to mean that the corresponding parameters differ by no more than 50%, in particular by no more than 30%, in particular by no more than 20%, in particular by no more than 10%, in particular by no more than 5%, in particular by no more than 3%, in particular by no more than 2%, in particular by no more than 1%.

[0128] The contrast layer 23 may be made, for example, by doping or ion implantation. i modified.

[0129] Contrast layer 23 i The contrast layer has a thickness D of the order of magnitude of a few nm, in particular in the range of 0.5 nm to 20 nm, in particular up to 10 nm. In particular, the contrast layer has a thickness corresponding to the layer 22 to be structured. i The maximum surface roughness of the surface roughness.

[0130] The layer 22 to be structured i and contrast layer 23 i In particular, it is applied by a roughness-preserving (in particular smoothing) process.

[0131] They are applied with great precision. The maximum thickness deviation over the optically useful surface area of ​​the optical component is in particular not more than 2%, in particular not more than 1%, in particular not more than 0.5%, in particular not more than 0.3%, in particular not more than 0.2%. i In the case of a layer thickness of the order of a few micrometers, the maximum thickness deviation may be in particular not greater than 50 nm, in particular not greater than 30 nm, in particular not greater than 20 nm, in particular not greater than 10 nm. i Also called shape-retaining layer or shaping layer.

[0132] If a layer has a constant thickness, the term shape-retaining layer is specifically used. Layers of varying thickness are called shaping layers.

[0133] After all layers to be structured 22 i and contrast layer 23 i After application to a substrate 20, an intermediate product 24 for producing an optical element is obtained. Figure 4 An example of an intermediate product 24 for producing a collector housing is shown. In this case, the substrate 20 has a curved surface, in particular an ellipsoid or a parabola.

[0134] The layer 22 to be structured i It is structured in a structuring step 25. For this purpose, a photolithography step 26 and a subsequent etching step 27 are provided.

[0135] For details on the structuring step, refer to DE 10 2018 220 629.5.

[0136] In a subsequent application step 36, a radiation-reflecting layer is applied. This is not shown in the drawing.

[0137] The radiation reflecting layer is in particular an EUV radiation reflecting layer. The radiation reflecting layer is in particular a layer stack made of a molybdenum-silicon bilayer.

[0138] The radiation reflecting layer and the shaping layer 22 to be structured i There may be further possible layers in between. In particular, a protective layer or other functional layers may be applied to the layer 22 to be structured. i , in particular applied to the layer 22 to be structured i on the top.

[0139] The radiation reflecting layer can be applied directly to layer 22 iDue to the low surface roughness of these layers, a previous polishing step can be omitted.

[0140] In principle, the uppermost layer 22 to be structured i Can also be polished.

[0141] The method described above leads to advantages in particular with regard to the integral parts of the collector 11, in particular the collector housing. This is due to the reduction of step depth errors. At the same time, the method according to the invention leads to a considerable simplification of the process chain, in particular to a reduction in throughput times. This is due to the fact that the polishing step is bypassed and the etching depth determination may be omitted.

[0142] Monitoring, in particular continuous monitoring, of the layer 22 to be structured in the etching step 27 i In particular, in this process, the detection reaches the contrast layer 23 i .

[0143] Contrast layer 23 i As an intermediate layer with a defined interval D n (s) and / or with a defined thickness T n (s) is introduced into the layer 22 to be structured i In this context, the parameter s specifies a position on the substrate and thus on the optical component to be produced therefrom.

[0144] After removing the contrast layer 23 i During this process, in particular by etching methods, these layers can be detected by mass spectrometry methods, in particular by residual gas analysis. i The removal can be detected in situ, especially in real time. i ,twenty three i+1 If the distance between is known, the etch rate can be determined from the time between the two peaks in the residual gas analysis. This can occur globally (ie, over the entire intermediate product) or locally.

[0145] By reducing the continuous contrast layer 23 i ,twenty three i+1 The distance between them is used to increase the accuracy of etching rate determination.

[0146] It may be provided that the contrast layer 23 i are arranged such that the distance between them increases with increasing distance from the substrate 20. This results in a greater distance between them at the beginning of the structuring process and in a shorter distance towards the end of the process and thus in a higher precision.

[0147] One or more contrast layers may be provided with a particular chemical signature which indicates that a certain depth is reached during etching.i Can be used as a signaling device, in particular as a stop signal.

[0148] In principle, any material which has a sufficiently high etching rate in the etching process used and which can be detected with sufficient accuracy by mass spectrometry methods can be used as the reference layer 23. i Advantageously, the contrast layer 23 i The layer 22 to be structured i However, they are different from the layer 22 to be structured. i different materials, for example by doping or ion implantation.

[0149] For example, contrast layer 23 i The contrast in the contrast layer can be established by a PVD method, wherein a silicon target or a silicon-filled crucible is used, wherein the target / crucible is doped with phosphorus for producing the contrast layer 23 i It is also possible to do so by ion implantation or by using a layer having a structure similar to the layer 22 to be structured. i Contrast is created by using materials with different chemical compositions but similar etching behaviors.

[0150] The layer 22 to be structured i Contrast between layers 23 i The arrangement of can have a gradient. This allows locally varying etching rates, such as can be provided for curved optical units, to be taken into account in a targeted manner.

[0151] exist Figure 5 In the example, a layer 22 to be structured is shown. i and contrast layer 23 i Detail of a cross section of an intermediate product 24 of the sequence. In this case, the contrast layer 23 increases with increasing distance from the substrate 20. i The distance between them increases.

[0152] exist Figure 6 In the example, the local removal of the layer 22 to be structured is shown. i and contrast layer 23 i The basis for later Figure 5 The state of the intermediate product 24. The etching depth can be determined by the amount of the contrast layer removed.

[0153] In the following, different aspects of the invention are described again in the form of keywords. These aspects each produce advantages individually or in combination.

[0154] Shape-retaining or shaping methods for depositing the layer to be structured 22 i Therefore, the layer 22 to be structured iAlso called the shaping layer.

[0155] Deposition methods, in particular roughness-retaining, preferably smooth deposition methods, are particularly useful for applying shaped layers. Thus, the layer has a specified layer thickness distribution and very low surface roughness immediately after its application.

[0156] Ion beam methods (especially reactive ion beam methods), plasma methods (especially reactive plasma methods), plasma jet methods, remote plasma methods, atomic layer etching (especially spatial atomic layer etching), electron beam assisted etching or other methods can be used to selectively remove the layer 22 to be structured. i and / or contrast layer 23 i In particular, it is possible to remove and / or smoothen these layers. Spatial atomic layer processing or processing with the aid of a focused electron beam can also be provided.

Claims

1. An intermediate product for producing an optical element of a projection exposure apparatus (1), the intermediate product comprising 1.

1. A substrate (20) for specifying the basic topography of the optical surface, 1.

2. wherein the layer to be structured (22 i ) and contrast layer (23 i ) are applied to the substrate (20), 1.

3. Wherein, the layer to be structured (22 i ) and the contrast layer (23) have different chemical properties, so that the contrast layer (23) can be detected in situ i ) removal.

2. The intermediate product according to claim 1, characterized in that The layer (22 ii ) is composed of materials whose etching rates in a specified etching method deviate from each other by no more than 10%.

3. The intermediate product according to any one of the preceding claims, characterized in that The layer (23 i ) is composed of materials whose densities differ by no more than 10%.

4. The intermediate product according to any one of the preceding claims, characterized in that The contrast layer (23 i ) and the layer to be structured (22 i ) have a starting material containing the same chemical element or the same compound, wherein the contrast layer (23 i )'s starting materials are modified by doping or ion implantation.

5. The intermediate product according to any one of the preceding claims, characterized in that The contrast layer (23 i ) has a thickness of no greater than 10 nm.

6. The intermediate product according to any one of the preceding claims, characterized in that The layer to be structured (22 i ) has a thickness in the range of 10 nm to 5 μm.

7. The intermediate product according to any one of claims 1 to 6, characterized in that The intermediate product comprises a plurality of contrasting layers (23 i ), the plurality of contrast layers (23 i ) in the layer to be structured (22 i ) to form an intermediate layer.

8. The intermediate product according to any one of claims 1 to 6, characterized in that The intermediate product comprises a plurality of contrasting layers (23 i ), wherein the contrast layer (23 i ) have different chemical compositions and / or different modifications.

9. The intermediate product according to any one of claims 1 to 6, characterized in that The intermediate product comprises a plurality of contrasting layers (23) having different distances therebetween. i ).

10. The intermediate product according to any one of the preceding claims, characterized in that The contrast layer (23 i ) and / or the layer to be structured (22 i ) has a thickness that varies within its range.

11. An optical element for a projection exposure apparatus (1) produced from an intermediate product as claimed in any one of the preceding claims.

12. A method for producing an intermediate product according to any one of claims 1 to 10, The following steps are involved: 12.

1. Providing a substrate (20) for specifying the basic topography of the optical surface, 12.

2. Applying a plurality of etchable layers to the substrate, wherein the layers include at least one layer to be structured (22 i ) and at least one contrast layer (23 i ), 12.

3. Among them, The layer to be structured (22 i ) and the contrast layer (23 i ) have different chemical properties, making it possible to detect the contrast layer in situ (23 i ) removal.

13. A method for producing an optical element for a projection exposure apparatus (1), The following steps are involved: 13.

1. Providing an intermediate product as claimed in any one of claims 1 to 10, 13.

2. Structuring the intermediate products, 13.

3. In situ monitoring of structuring processes.

14. The method according to claim 13, characterized in that The monitoring of the structuring process comprises an in-situ analysis of the removed layer, wherein an evaluation of this analysis is used as a control signal for a further structuring process.

15. A device for producing an optical element for a projection exposure device (1), comprising 15.

1. Vacuum chamber for receiving intermediate products for producing optical elements of a projection exposure apparatus (1), 15.

2. means for structuring the intermediate product in the vacuum chamber, 15.

3. Means for in-situ monitoring of the structuring of the intermediate product, 15.

4. Among them, The device for monitoring the structuring of the intermediate product is coupled in a data transmission manner to the device for structuring the intermediate product in the vacuum chamber.

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