Optical components and optical systems, especially for microlithography

Abstract

Optical components and systems for microlithography are provided. [Solution] The optical component comprises a first layer system (210) that exhibits a first wavelength-dependent reflectance curve when struck by electromagnetic radiation, and at least one second layer system (220) that exhibits a second wavelength-dependent reflectance curve when struck by electromagnetic radiation, wherein the first layer system and the second layer system are disposed on different optical surfaces, and the wavelength dependences of the first reflectance curve and the second reflectance curve at least partially compensate each other such that the resulting total reflectance of the first layer system and the at least one second layer system has a relative deviation of 5% or less from a desired reflectance curve that is linear or constant with respect to wavelength within a specified wavelength range.

Description

[Technical Field]

[0001] This patent application claims priority from German patent application DE 102022113164.5, filed with the German Patent and Trademark Office on May 24, 2022. The content of German patent application DE 102022113164.5 is incorporated by reference into this patent application.

[0002] The present invention relates to optical components and optical systems. The invention can be advantageously applied to, for example, laser light sources, but can also be used in other applications, in particular in microlithographic projection exposure apparatus. [Background technology]

[0003] Microlithography is used to manufacture finely structured electronic components. The microlithography process is carried out in an apparatus known as a projection exposure apparatus, which comprises an illumination device and a projection lens. The image of a mask (= reticle) illuminated by the illumination device is projected by the projection lens onto a substrate (e.g. a silicon wafer) coated with a photosensitive layer (photoresist), which is located in the image plane of the projection lens, in order to transfer the mask structure into the photosensitive coating of the structure.

[0004] In projection exposure apparatus designed to operate in the DUV range (e.g., operating wavelengths below 250 nm, in particular below 200 nm), laser light sources in the form of excimer lasers, in particular krypton fluoride excimer lasers with an operating wavelength of 248 nm, or argon fluoride excimer lasers with an operating wavelength of 193 nm, are typically used.

[0005] Existing challenges in the area of ​​development of projection exposure apparatus relate inter alia to the microlithographic production of ever smaller structures and the ever stricter requirements regarding the accuracy of their positioning on the wafer.

[0006] A problem that arises in optical components, for example in the aforementioned laser light sources, but also in illumination devices, projection lenses or other optical systems, is that degradation of the material of the components caused by the respective ambient conditions (e.g., by exposure to electromagnetic radiation, ions, etc.) leads to changes in their optical properties, which are accompanied by a deterioration in the performance of the optical system that includes them.

[0007] For example, ambient conditions can cause unwanted changes in the wavelength-dependent reflection or transmission curves of beam splitters used in optical systems, such as the aforementioned laser light sources, which - as shown in the merely exemplary diagram of Figure 13 - ultimately correspond to a shift in the effective wavelength of the electromagnetic radiation incident on the component in terms of their effect on reflection or transmission behavior. Optical components are in principle designed for the respective operating wavelength of the optical system (e.g. 193 nm) and therefore no longer exhibit their optimal behavior when the effective wavelength shifts in this way, which consequently impairs the performance of the optical system and, in the example of the aforementioned laser light source, leads to unwanted variations in the respective delivered light source power.

[0008] With regard to the prior art, reference is made only to European Patent No. EP 3 111 257 as an example. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. EP 3 111 257 Summary of the Invention

[0010] SUMMARY OF THE INVENTION It is an object of the present invention to provide optical components and an optical system which avoid at least to some extent the problems mentioned above, while allowing operation as stable as possible even under changing conditions of use.

[0011] This object is achieved by an optical component according to the features of independent patent claim 1 and by an optical system according to the features of alternative independent patent claim 13.

[0012] According to the invention, the optical component comprises: a first layer system that exhibits a first wavelength-dependent reflectance curve when struck by electromagnetic radiation; - at least one second layer system exhibiting a second wavelength-dependent reflectance curve when struck by electromagnetic radiation, the first layer system and the second layer system are arranged on different optical surfaces; - the wavelength dependences of the first and second reflectance curves at least partially compensate each other so that the resulting total reflectance of the system of first layers and the system of at least one second layer has a relative deviation of no more than 5% from a desired reflectance curve that is linear or constant with wavelength within a specified wavelength range.

[0013] In particular, the invention is based on the idea of ​​designing the respective wavelength-dependent reflectance curves of the layer systems present on the different optical surfaces of the component in such a way that, even in the event of drifts in the respective reflectance behavior of the layer systems in question, caused for example by things in the component's surroundings and in particular by contamination or degradation, the resulting total reflectance behavior of the optical component remains at least approximately constant or at least only slightly deviates from the desired linear reflectance curve with respect to wavelength.

[0014] In other words, the invention takes the approach of matching the layer systems located on at least two optical surfaces of a component to one another in such a way that their respective wavelength-dependent reflectance curves, which are intentionally allowed for each of the individual layer systems in question, at least partially compensate each other, so that for the layer systems in question or for the respective optical component as a whole, there is no longer, or only a small, spectral drift in the reflectance behavior that is problematic from the perspective of the performance of the optical system.

[0015] The present invention, which allows for intentional, reversible structural changes and the accompanying spectral shifts in the reflection behavior of each individual layer system of the aforementioned layer systems, makes it possible to ensure a stable and almost constant operation even in the case of relatively problematic ambient conditions in terms of the risk of degradation or contamination (for example, in the wavelength range of 100 nm to 700 nm, in particular in the wavelength range of 100 nm to 400 nm, which is due to the relatively high energy of the electromagnetic radiation and the atmosphere optionally present in the respective optical system), and especially also when these ambient conditions vary over time, since, as mentioned above, the layer systems in question are in a sense "pitted" against each other in terms of the influence of the above-mentioned changes during operation.

[0016] According to the present invention, even in the case of optical systems with a practically constant operating wavelength (e.g. laser light sources), the disadvantage of increased expenditure for constructing respective layer designs on different surfaces of the optical component due to the mutual compensation associated with the respective wavelength-dependent reflectivity curves is intentionally tolerated, since in return, such construction makes it possible to accommodate the effects of degradation or reversible structural changes in the sense of the shift in effective wavelength in the reflection behavior mentioned at the beginning.

[0017] The reflectivity of the second layer system can also be equal to zero, in which case the resulting reflectivity within the specified wavelength range corresponds to the reflectivity of the first layer system.

[0018] According to one embodiment, the wavelength dependencies of the first and second reflectance curves at least partially compensate each other so that the resulting total reflectance of the system of first layers and the system of at least one second layer has a relative deviation of no more than 3%, in particular no more than 2%, from a desired reflectance curve that is linear or constant with wavelength within a specified wavelength range.

[0019] According to one embodiment, the resulting total reflectance of the first layer system and the at least one second layer system is constant within the specified wavelength range except for a maximum relative variation of 5%, in particular except for a maximum relative variation of 3%, and more particularly except for a maximum relative variation of 2%.

[0020] According to one embodiment, the maximum variation in reflectance for the resulting reflectance curve within the specified wavelength range is less than the respective maximum variations in reflectance for the first wavelength-dependent reflectance curve and for the second wavelength-dependent reflectance curve within the specified wavelength range.

[0021] In the first reflectance curve of the first layer system, the reflectance as a function of wavelength varies, according to one embodiment, within a particular wavelength range by at least 5%, in particular by at least 10%, relative to the maximum reflectance.

[0022] According to an embodiment, the optical component further comprises at least one third layer system having a third wavelength-dependent reflectance curve.

[0023] In one embodiment, the relative deviation of the resulting total reflectance of the first layer system, the second layer system, and the third layer system from the desired linear reflectance curve within the specified wavelength range is 5% or less, particularly 3% or less, and more particularly 2% or less.

[0024] According to an embodiment, the specified wavelength range extends for a given operating wavelength λ0 from 0.95λ0 to 1.05λ0, in particular from 0.9λ0 to 1.1λ0, more particularly from 0.8λ0 to 1.2λ0, and even more particularly from 0.7λ0 to 1.3λ0.

[0025] According to an embodiment, the optical component comprises at least one beam splitter.

[0026] According to an embodiment, the optical component comprises an output coupling element for output coupling the component beams from the optical beam path of the optical system.

[0027] According to an embodiment, the optical component comprises a deflecting element for deflecting the component beams within the optical beam path of the optical system.

[0028] According to one embodiment, the optical components are designed for an operating wavelength in the range of 100 nm to 700 nm.

[0029] Furthermore, the invention also relates to an optical system, in particular for microlithography, comprising an optical component according to the above-mentioned characteristics, in particular, although the invention is not limited thereto, that can be arranged within a laser light source.

[0030] Further embodiments of the invention are evident from the present description and the dependent claims.

[0031] The invention will now be explained in more detail on the basis of exemplary embodiments shown in the accompanying drawings. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a diagram illustrating the concept underlying the present invention. [Figure 2] 1 is a schematic diagram of a possible basic structure of a beam splitter in which the present invention can be implemented; [Figure 3a] 1 is a diagram illustrating a possible embodiment of the present invention. [Figure 3b] 1 is a diagram illustrating a possible embodiment of the present invention. [Figure 4] 1 is a diagram illustrating a possible embodiment of the present invention. [Figure 5] 1 is a diagram illustrating a possible embodiment of the present invention. [Figure 6] 1 is a diagram illustrating a possible embodiment of the present invention. [Figure 7] 1 is a schematic diagram of exemplary optical components in which the present invention may be implemented; [Figure 8] 1 is a schematic diagram of exemplary optical components in which the present invention may be implemented; [Figure 9]1 is a schematic diagram of exemplary optical components in which the present invention may be implemented; [Figure 10] 1 is a schematic diagram of exemplary optical components in which the present invention may be implemented; [Figure 11] 1A and 1B are schematic diagrams illustrating possible architectures of a microlithographic projection exposure apparatus designed to operate in DUV; [Figure 12] 1 is a schematic diagram illustrating an exemplary application of the present invention; [Figure 13] 1 is a diagram for explaining a problem that occurs in the case of the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, an embodiment of the present invention will be described with reference to the diagrams of FIGS. 3a to 6, and the schematic diagrams of FIG. 2 and FIGS.

[0034] Common to the embodiments described below is that - with the objective of avoiding changes in optical performance due to degradation during operation of an optical component or an optical system comprising said component - at least two layer systems located on different surfaces of said optical component are matched to each other in terms of their respective wavelength-dependent reflectance behavior in order to obtain at least a partial compensation effect and an overall almost constant reflectance behavior of the optical component in terms of the effects of degradation or structural changes.

[0035] In doing so, the invention proceeds in particular from the idea that—as already explained at the beginning with the diagram of Fig. 13—degradation of the material of an optical component, such as a beam splitter, ultimately corresponds to a shift in the effective wavelength in terms of its influence on the reflective behavior of the optical component, which shift, without appropriate countermeasures, will entail impairment of the performance of the optical component (which of course is initially constructed in a manner that targets the specific operating wavelength of the respective optical system). According to the invention, these situations are addressed by the required substantially plateau-shaped wavelength-dependent reflectivity curve for the entire component for the optical component—despite being intended for use only at a specific operating wavelength (e.g., 193 nm)—even over a relatively large wavelength range, since, as a result of this plateau-shaped curve, as shown in Fig. 1, the aforementioned degradation-related shift in the effective wavelength no longer leads to impairment of the light reflective behavior.

[0036] As will be described below on the basis of various embodiments with reference to Figures 2 to 10, a substantially constant performance of the optical component in terms of reflection behavior is achieved overall in accordance with the invention in that at least two layer systems located on different surfaces of the optical component have in a sense contrasting wavelength-dependent reflectance curves and are therefore "pitted against one another" or matched to one another in the sense of mutual compensation with regard to their respective degrading effects.

[0037] In particular, although the invention is not limited thereto, the concept according to the invention can be realized in an optical component in the form of an optical beam splitter, for example as used in laser light sources or other optical systems, in particular for microlithography. According to the purely schematic illustration of Figure 2, such a beam splitter 200 can consist of a first layer system 210 and a second layer system 220, which further shows that for an incident light beam of intensity I0, the reflected intensity component I R and transmitted intensity component I TThe resulting overall reflectance and corresponding overall transmittance of beamsplitter 200 are both composed of the properties of the two layer systems 210, 220, and the overall reflectance, neglecting optical losses, appears as:

[0038]

number

[0039] For an exemplary realization of the concepts according to the present invention, Figure 3a now shows possible wavelength-dependent reflectance curves for a first layer system 210, and Figure 3b shows wavelength-dependent reflectance curves for a second layer system 220 suitable for achieving the desired compensation effect according to the present invention. As is clear from Figures 3a-b, significant variations in the individual wavelength-dependent reflectance curves are clearly "tolerated" in the process, although these wavelength-dependent variations (including the intermediate extremes present in this particular example) run exactly counter to or complementary to each other.

[0040] FIG. 4 shows a further example of the matching of two layer systems of an optical component, such as an optical beam splitter, with one another according to the invention, where the reflectance curve of the second layer system (illustrated using a dashed line) again runs exactly inversely to the reflectance curve of the first layer system (illustrated using a solid line).

[0041] To illustrate specific exemplary embodiments, Table 1 shows possible layer designs for the first layer system, and Table 2 shows preferred layer designs for the second layer system suitable for achieving the desired compensation effect.

[0042] Table 1: [Table 1]

[0043] Table 2: [Table 2]

[0044] In this regard, Figure 5 shows the corresponding wavelength-dependent reflectance curves, showing both the desired target profile for an ideal compensation effect and the actual profile achieved by the specific layer design for the second layer system. As can be seen from Figure 5, a nearly plateau-shaped curve is achieved for the resulting overall reflectance over a relatively wide wavelength range from about 160 nm to 240 nm.

[0045] As further specific exemplary embodiments, Table 3 shows further possible layer designs of the first layer system, and Table 4 shows correspondingly matched layer designs of the second layer system suitable for obtaining the compensation effect according to the invention.

[0046] Table 3: [Table 3]

[0047] Table 4: [Table 4]

[0048] In a similar manner to FIG. 5, FIG. 6 shows the respective wavelength-dependent reflectance curves for the exemplary embodiments of Tables 3-4.

[0049] The present invention is not limited to realizing two mutually matched layer systems on an optical component. Figure 7 shows, in a purely schematic view, an optical component 700 made up of two partial components 701, 702, where partial component 701 is again an optical beam splitter and partial component 702 is a mirror. As a result, component 700 can utilize a total of three optically effective surfaces or layer systems 710, 720, 730 present on these surfaces, which can be matched to one another with respect to their respective wavelength-dependent reflectance curves in order to obtain the compensation effect according to the invention.

[0050] 8 shows a further application example of an optical component 800, on whose surfaces three optically effective surfaces or layer systems 810, 820, 830 are located. In this case, optical component 800 selectively acts either as a deflecting mirror (for the portion reflected by layer system 830 and transmitted through layer system 820) or as an output coupling element (for the portion transmitted through layer system 830). Depending on the specific use scenario, layer systems 820 and 830, for example, can be matched to one another in accordance with the invention so that the proportion of the portions transmitted therethrough in each case remains constant over a sufficiently wide wavelength range.

[0051] 9 shows in a schematic diagram a further example of an optical component 900 made up of two partial components 901, 902, each in the form of a beam splitter, so that a total of four optically effective surfaces or systems of layers located on these surfaces 910, 920, 930 and 940 are available for obtaining the compensation effect according to the invention.

[0052] As a further example of a possible application, Fig. 10 shows an optical component 1000 in the form of a deflection or output coupling element, in which three different optical surfaces or layer systems 1010, 1020, 1030 located on those surfaces are available, of which layer system 1010 is passed through twice according to the beam path shown. As shown in Fig. 10, optical component 1000 can be used to output two different component beams (corresponding to the part transmitted through layer system 1020 and the part transmitted through layer system 1030). Furthermore, depending on the specific use scenario, all three layer systems, or alternatively only two of these layer systems, can be matched to each other in terms of their wavelength-dependent reflectance curves in a manner according to the invention.

[0053] FIG. 11 shows a possible architecture in principle of a microlithography projection exposure apparatus 1100 designed to operate in the DUV.

[0054] The projection exposure apparatus 1100 according to Fig. 11 comprises an illumination device 1110 and a projection lens 1120. The illumination device 1110 serves to illuminate a structured mask (reticle) 1115 with light from a light source unit 1105, which comprises a laser light source, for example in the form of an ArF excimer laser for an operating wavelength of 193 nm (or else in the form of a KrF excimer laser for an operating wavelength of 248 nm), and a beam-shaping optical unit furthermore generating a collimated light beam. In this case, the laser light source can be designed in a manner according to the invention.

[0055] The illumination device 1110 comprises, inter alia, an optical unit 1111 which, in the example shown, comprises a deflection mirror 1112. The optical unit 1111 can comprise, for example, a diffractive optical element (DOE) and a zoom axicon system for obtaining various illumination settings (i.e., intensity distributions in the pupil plane of the illumination device 1110). A light mixing device (not shown) is located in the beam path downstream in the light propagation direction of the optical unit 1111 and can, for example, in a manner known per se, comprise an arrangement of micro-optical elements suitable for achieving light mixing and a group of lens elements 1113, downstream of which is a field plane with a reticle masking system (REMA), which is imaged by a REMA lens 1114 arranged downstream in the light propagation direction onto a mask (reticle) 1115 having structures arranged in a further field plane, thereby defining an illumination area on the reticle. By means of the projection lens 1120, the mask 1115 with the structure is imaged onto a substrate with a photosensitive layer (photoresist) or onto a wafer 1130. In particular, the projection lens 1120 can be designed for immersion operation, in which case the immersion medium is located upstream of the wafer or its photosensitive layer in relation to the light propagation direction. Furthermore, the projection lens 1120 can have a numerical aperture NA, for example, greater than 0.85, in particular greater than 1.1.

[0056] Figure 12a shows, purely diagrammatically, a laser 1210 into which a beam splitter 1211 has been inserted, as an exemplary application of the invention. By way of example, beam splitters may also be used in optical pulse stretchers or for the purpose of output coupling of component beams, e.g., for beam measurement purposes. Figure 12b also shows, purely diagrammatically, a microscope 1220 (e.g., for wafer inspection) into which a beam splitter 1221 has been inserted, as an exemplary application of the invention.

[0057] While the present invention has also been described based on particular embodiments, numerous variations and alternative embodiments will be apparent to those skilled in the art, e.g., by combining and / or substituting features of the particular embodiments. Accordingly, it will be readily apparent to those skilled in the art that the present invention concomitantly encompasses such variations and alternative embodiments, and that the scope of the present invention is limited only within the meaning of the appended claims and equivalents thereof.

Claims

1. An optical component comprising an optical surface, A system of first layers configured to exhibit a first wavelength-dependent reflectance curve when exposed to electromagnetic radiation, A system comprising a second layer configured to exhibit a second wavelength-dependent reflectance curve when struck by electromagnetic radiation, The first layer system and the second layer system are located on different optical surfaces of the optical element. For each wavelength across the entire wavelength range from 100 nm to 700 nm, the total wavelength-dependent reflectance curve is the sum of the first wavelength-dependent reflectance curve and the second wavelength-dependent reflectance curve. Over the entire wavelength range from 160 nm to 240 nm, the total wavelength-dependent reflectance curve deviates from a constant value by 5% or less. Optical components.

2. The optical component according to claim 1, wherein the total wavelength-dependent reflectance curve deviates by 3% or less from the constant value over the entire wavelength range of 160 nm to 240 nm.

3. The optical component according to claim 1, wherein the total reflectance of the system of the first layer and the system of the second layer are constant over the entire wavelength range of 160 nm to 240 nm, except for a maximum relative variation of 5%.

4. The optical component according to claim 1, wherein, over the entire wavelength range of 160 nm to 240 nm, the maximum variation of the total wavelength-dependent reflectance curve is smaller than the maximum variation of the reflectance for the first wavelength-dependent reflectance curve and the second wavelength-dependent reflectance curve, respectively.

5. The optical component according to claim 1, wherein the reflectance of the first wavelength-dependent reflectance curve varies by at least 5% with respect to the maximum reflectance of the first wavelength-dependent reflectance curve over the entire wavelength range of 160 nm to 240 nm.

6. The optical component according to claim 1, further comprising a system of third layers having a third wavelength-dependent reflectance curve.

7. The optical component according to claim 6, wherein the resulting total reflectance of the first layer system, the second layer system, and the third layer system is 5% or less of the constant value over the entire wavelength range of 160 nm to 240 nm.

8. The optical component according to claim 1, wherein the optical component comprises a beam splitter.

9. The optical component according to claim 1, wherein the optical component comprises an output coupling element configured to output couple component beams from the optical beam path.

10. The optical component according to claim 1, wherein the optical component comprises a deflection element configured to deflect a component beam within the optical beam path.

11. An optical system comprising the optical components described in claim 1, wherein the optical system is a microlithography optical system.

12. An optical system having a first optical surface and a second optical surface, A system of first layers configured to exhibit a first wavelength-dependent reflectance curve when exposed to electromagnetic radiation, A system comprising a second layer configured to exhibit a second wavelength-dependent reflectance curve when struck by electromagnetic radiation, The first optical surface differs from the second optical surface, The system of the first layer is supported by the first optical surface, The system of the second layer is supported by the second optical surface, For each wavelength across the entire wavelength range from 100 nm to 700 nm, the total wavelength-dependent reflectance curve is the sum of the first wavelength-dependent reflectance curve and the second wavelength-dependent reflectance curve. Over the entire wavelength range from 160 nm to 240 nm, the total wavelength-dependent reflectance curve deviates from a constant value by 5% or less. Optical components.

13. The optical component according to claim 12, wherein over the entire wavelength range of 160 nm to 240 nm, the first wavelength-dependent reflectance curve and the second wavelength-dependent reflectance curve at least partially compensate for each other such that the relative deviation from the constant value with respect to the total wavelength-dependent reflectance curve is 3% or less.

14. The optical component according to claim 12, wherein the total wavelength-dependent reflectance curve has a maximum relative variation of 5% from constant to a maximum in the wavelength range of 160 nm to 240 nm.

15. Over the entire wavelength range of 160 nm to 240 nm, The maximum variation in reflectance for the total wavelength-dependent reflectance curve is smaller than the maximum variation in reflectance for the first wavelength-dependent reflectance curve. The maximum variation in reflectance for the total wavelength-dependent reflectance curve is smaller than the maximum variation in reflectance for the second wavelength-dependent reflectance curve. The optical component according to claim 12.

16. The optical component according to claim 1, wherein the reflectance of the first wavelength-dependent reflectance curve varies by at least 5% from the maximum reflectance of the first wavelength-dependent reflectance curve over the entire wavelength range of 160 nm to 240 nm.

17. The optical component further comprises a system of third layers having a third wavelength-dependent reflectance curve, The optical component according to claim 12, wherein the resulting total reflectance deviation of the system of the first layer, the system of the second layer, and the system of the third layer over the entire wavelength range of 160 nm to 240 nm is 5% or less from the constant value.

18. An optical system comprising the optical components described in claim 12, wherein the optical system is a microlithography optical system.

19. For each wavelength within the entire wavelength range of 160 nm to 240 nm, The system of the first layer is configured to reflect a first portion of electromagnetic radiation at the wavelength, and the first portion of electromagnetic radiation is greater than zero. The system of the first layer is configured to reflect a second portion of electromagnetic radiation at the wavelength, and the second portion of electromagnetic radiation is greater than zero. The second layer system is configured to reflect the third portion of the electromagnetic radiation at the aforementioned wavelength, and the third portion of the electromagnetic radiation is greater than zero. The second layer system is configured to reflect the fourth portion of the electromagnetic radiation at the aforementioned wavelength, wherein the fourth portion of the electromagnetic radiation is greater than zero. The optical component according to claim 12, wherein the optical component is configured to be such as.

20. For each wavelength within the entire wavelength range of 160 nm to 240 nm, The system of the first layer is configured to reflect a first portion of electromagnetic radiation at the wavelength, and the first portion of electromagnetic radiation is greater than zero. The system of the first layer is configured to reflect a second portion of electromagnetic radiation at the wavelength, and the second portion of electromagnetic radiation is greater than zero. The second layer system is configured to reflect the third portion of the electromagnetic radiation at the aforementioned wavelength, and the third portion of the electromagnetic radiation is greater than zero. The second layer system is configured to reflect the fourth portion of the electromagnetic radiation at the aforementioned wavelength, wherein the fourth portion of the electromagnetic radiation is greater than zero. The optical component according to claim 1, wherein the optical component is configured to be such as.

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