Optical component and optical system, especially for microlithography

Abstract

Optical component, with: • a first layer system (210, 710, 810, 910, 1010) which, when exposed to electromagnetic radiation, has a first wavelength-dependent reflectivity profile; and • at least one second layer system (220, 720, 820, 920, 1020) which, when exposed to electromagnetic radiation, has a second wavelength-dependent reflectivity profile; • wherein the first layer system (210, 710, 810, 910, 1010) and the second layer system (220, 720, 820, 920, 1020) are arranged on different optical surfaces; and • wherein the wavelength dependencies of the first and second reflectivity curves at least partially compensate each other such that for a total reflectivity resulting for the first layer system (210, 710, 810, 910, 1010) and the at least one second layer system (220, 720, 820, 920, 1020) in the predetermined wavelength range, the relative deviation from a desired reflectivity curve that is linear or constant with respect to the wavelength is a maximum of 5%; and • wherein the optical component comprises at least one beam splitter.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The invention relates to an optical component and an optical system. The invention is advantageously applicable, for example, in a laser light source, but also in other applications, and in particular for use in a microlithographic projection exposure system. State of the art

[0002] Microlithography is used to manufacture microstructured electronic components. The microlithography process is carried out in a projection exposure system, which has 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 light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] In a projection exposure system designed for operation in the DUV range (e.g. at working wavelengths of less than 250 nm, in particular less than 200 nm), laser light sources in the form of excimer lasers are typically used, in particular krypton fluoride excimer lasers at a working wavelength of 248 nm or argon fluoride excimer lasers at a working wavelength of 193 nm.

[0004] Challenges arising in the development of projection exposure systems include increasing accuracy requirements for the microlithographic production of ever smaller structures and their positioning on the wafer.

[0005] A problem that occurs with optical components, e.g. in the above-mentioned laser light sources, but also in the lighting device, in the projection lens or in other optical systems, is that degradations in the material of the components, which are caused by the respective environmental conditions (e.g. by exposure to electromagnetic radiation, ions, etc.), lead to changes in the respective optical properties, which in turn is accompanied by an impairment of the performance of the optical system containing the component in question.

[0006] For example, in optical systems such as the laser light sources mentioned above, beam splitters used can, depending on the ambient conditions, cause undesired changes in the wavelength-dependent reflection or transmission curve, which - as shown in the merely exemplary diagram of Fig.13, their effect on the reflection or transmission behavior ultimately corresponds to a shift in the effective wavelength of the electromagnetic radiation incident on the component in question. The optical component, which is usually designed for the respective operating wavelength of the optical system (e.g., 193 nm), then no longer exhibits its optimal behavior with this shift in the effective wavelength, so that the performance of the optical system is also impaired. In the above-mentioned example of the laser light source, for example, the source power provided is subject to undesirable fluctuations.

[0007] US 2013 / 0250405 A1 discloses, among other things, a broadband mirror which is constructed from separate microlayer stacks, whereby a comparatively broad reflectivity band in the visible and infrared wavelength range is provided by overlapping the individual reflection bands of the different microlayer stacks.

[0008] DE 102 48 707 A1 discloses, inter alia, a highly reflective mirror with a substrate for an excimer laser, wherein the mirror has a first highly reflective layer system on the substrate inner side facing the laser-active medium for reflecting a first wavelength and a second highly reflective layer system on the substrate outer side facing away from the substrate inner side for reflecting a second wavelength, and wherein the first wavelength differs from the second wavelength.

[0009] For further prior art, reference is made to EP 3 111 257 B1 as an example. SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide an optical component and an optical system which enable the most stable operation possible even under varying operating conditions while at least partially avoiding the problems described above.

[0011] This object is achieved by the optical component according to the features of independent patent claim 1 or the optical system according to the features of the independent patent claim 12.

[0012] According to the invention, an optical component comprises: - a first layer system which, when exposed to electromagnetic radiation, has a first wavelength-dependent reflectivity profile; and - at least one second layer system which, when exposed to electromagnetic radiation, has a second wavelength-dependent reflectivity profile; - wherein the first layer system and the second layer system are arranged on different optical surfaces; and - wherein the wavelength dependencies of the first and second reflectivity curves at least partially compensate each other such that, for a total reflectivity resulting for the first layer system and the at least one second layer system in the predetermined wavelength range, the relative deviation from a desired reflectivity curve that is linear or constant with respect to the wavelength is a maximum of 5%; and - wherein the optical component comprises at least one beam splitter.

[0013] The invention is based in particular on the concept of designing layer systems present on different optical surfaces of a component with regard to their respective wavelength-dependent reflectivity profile in such a way that even in the event of a drift in the respective reflectivity behavior of the layer systems in question, e.g. caused by the environment of the component and in particular by contamination or degradation, the overall resulting reflectivity behavior of the optical component remains at least largely constant or at least deviates only slightly from a desired linear reflectivity profile with respect to the wavelength.

[0014] In other words, the present invention pursues the approach of coordinating the layer systems located on at least two optical surfaces of a component in such a way that the respective wavelength-dependent reflectivity curves - which are deliberately permitted for each of the respective layer systems - at least partially compensate for one another, with the result that for the entirety of the respective layer systems or the respective optical component, a spectral drift in the reflection behavior that is problematic with regard to the performance of the optical system does not occur or only occurs to a small extent.

[0015] Since, according to the invention, deliberately reversible structural changes and the associated spectral shifts in the reflection behavior can be accepted for each individual layer system mentioned above, stable or largely constant operation can be guaranteed at all times, even in the case of ambient conditions that are comparatively problematic with regard to the risk of degradation or contamination (e.g. in the wavelength range from 100 nm to 700 nm, in particular from 100 nm to 400 nm due to the comparatively high-energy electromagnetic radiation and the atmosphere that may be present in the respective optical system) and in particular even when these ambient conditions vary over time, since, as described above, the layer systems in question are to a certain extent "played off" against each other with regard to the effects of said changes in operation.

[0016] According to the invention, the disadvantage of increased effort for the design of the respective layer designs on different surfaces of the optical component with regard to mutual compensation with regard to the respective wavelength-dependent reflectivity curve is deliberately accepted, even in an optical system with an actually constant working wavelength (such as a laser light source), since in return this design can take into account the effects of degradations or reversible structural changes in the sense of the shift in the effective wavelength in the reflection behavior described at the beginning.

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

[0018] According to one embodiment, the wavelength dependencies of the first and second reflectivity curves at least partially compensate for one another in such a way that for a reflectivity resulting in total for the first layer system and the at least one second layer system in the predetermined wavelength range, the relative deviation from a desired reflectivity curve that is linear or constant with respect to the wavelength is at most 3%, in particular by a maximum of 2%.

[0019] According to one embodiment, a total reflectivity resulting for the first layer system and the at least one second layer system in the predetermined wavelength range is constant up to a maximum relative variation of 5%, in particular up to a maximum relative variation of 3%, further in particular up to a maximum relative variation of 2%.

[0020] According to one embodiment, for the resulting reflectivity profile, a maximum variation of the reflectivity in the predetermined wavelength range is smaller than the respective maximum variation of the reflectivity in the predetermined wavelength range for the first wavelength-dependent reflectivity profile and for the second wavelength-dependent reflectivity profile.

[0021] According to one embodiment, in the first reflectivity profile of the first layer system, the reflectivity varies as a function of the wavelength in the predetermined wavelength range by at least 5%, in particular by at least 10%, based on the maximum reflectivity.

[0022] According to one embodiment, the optical component further comprises at least one third layer system with a third wavelength-dependent reflectivity profile.

[0023] According to one embodiment, for a total reflectivity resulting for the first layer system, the second layer system and the third layer system in the predetermined wavelength range, the relative deviation from a desired linear reflectivity curve is a maximum of 5%, in particular a maximum of 3%, further in particular a maximum of 2%.

[0024] According to one embodiment, the predetermined wavelength range for a predetermined working wavelength λ0 extends from 0.95*λ0 to 1.05*λ0, in particular from 0.9*λ0 to 1.1*λ0, further in particular from 0.8*λ0 to 1.2*λ0, and further in particular from 0.7*λ0 to 1.3*λ0.

[0025] According to the invention, the optical component has at least one beam splitter.

[0026] According to one embodiment, the optical component has a coupling-out element for coupling out a partial beam from the optical beam path of an optical system.

[0027] According to one embodiment, the optical component has a deflection element for deflecting a partial beam in the optical beam path of an optical system.

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

[0029] The invention further relates to an optical system, in particular for microlithography, comprising an optical component according to the features described above. The optical component can be arranged in particular (but without the invention being limited thereto) in a laser light source.

[0030] Further embodiments of the invention can be found in the description and the subclaims.

[0031] The invention is explained in more detail below with reference to an embodiment shown in the attached figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] They show: Fig. 1 is a diagram for explaining a concept underlying the present invention; Fig. 2 a schematic representation of the basic possible structure of a beam splitter in which the present invention can be implemented; Fig. 3a-6 diagrams for explaining possible embodiments of the present invention; Fig. 7-10 are schematic representations of exemplary optical components in which the present invention can be implemented; Fig. 11 a schematic diagram to explain the possible structure of a microlithographic projection exposure system designed for operation in DUV; Fig. 12a-12b are schematic representations of exemplary applications of the invention; and Fig. 13 is a diagram illustrating a problem occurring in the prior art. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] Hereinafter, embodiments of the present invention will be described with reference to the diagrams in Fig. 3a-6 and the schematic representations of Fig. 2 and Fig. 7-10 explained.

[0034] The embodiments described below have in common that - with the aim of avoiding a change in the optical performance occurring during operation of an optical component or of an optical system comprising this component due to degradation - at least two layer systems located on different surfaces of the optical component in question are coordinated with one another in their respective wavelength-dependent reflectivity behavior in such a way that an at least partial compensation effect and overall a largely constant reflectivity behavior of the optical component is achieved with regard to the effects of a degradation or structural change.

[0035] The present invention is based in particular on the consideration that - as already explained in the introduction using the diagram of Fig.13 explains - a degradation in the material of an optical component such as a beam splitter, in its effect on the reflection behavior of the optical component, ultimately corresponds to a shift in the effective wavelength, which, without suitable countermeasures, is accompanied by an impairment of the performance of the respective optical component (which was initially specifically designed for the specific operating wavelength of the respective optical system). According to the invention, this circumstance is now taken into account by striving for an essentially plateau-shaped wavelength-dependent reflectivity curve for the component as a whole, even over a larger wavelength range, for the respective optical component - despite its intended use only for a specific operating wavelength (e.g., 193 nm), since then, as a result of this plateau-shaped curve, as in Fig.1 indicates that the said degradation-related shift in the effective wavelength no longer leads to any impairment in the optical reflection behavior.

[0036] As will be explained below with reference to different embodiments and Fig. 2 to Fig. 10, the essentially constant performance for the optical component as a whole with regard to the reflection behavior is achieved according to the invention in that at least two layer systems located on different surfaces of the optical component have, so to speak, opposing wavelength-dependent reflectivity curves and are thus "played off against each other" with regard to their respective degradation effect or are coordinated with each other in the sense of mutual compensation.

[0037] The inventive concept can be implemented in particular (but without the invention being limited thereto) in an optical component in the form of an optical beam splitter, such as is used in a laser light source or in other optical systems, in particular for microlithography. According to the merely schematic representation of Fig. 2, such a beam splitter 200 can be constructed from a first layer system 210 and a second layer system 220, wherein in Fig. 2 furthermore, for an incident light beam with intensity I0 both the creation of a reflected intensity component I R as well as a transmitted intensity component I TBoth the total reflectivity and the corresponding total transmissivity resulting for the beam splitter 200 are composed of the respective properties of the two layer systems 210, 220, whereby the total reflectivity, neglecting optical losses, is Rtotal=r1+(1−r1)2r21−r1r2 . Here, r1 and r2 denote the respective partial reflectivities of the first and second layer systems 210, 220.

[0038] For an exemplary realization of the inventive concept, Fig. 3a shows a possible wavelength-dependent reflectivity curve for the first layer system 210, and Fig. 3b shows a wavelength-dependent reflectivity curve for the second layer system 220, which is suitable according to the invention for achieving the desired compensation effect. Fig.3a-3b clearly show that significant variations are “allowed” for the individual wavelength-dependent reflectivity curves, although these wavelength-dependent variations (including the intermediate extremes present in the concrete example) run in opposite or complementary directions to each other.

[0039] Fig. 4 shows a further example of the inventive coordination of two layer systems of an optical component such as an optical beam splitter, wherein the reflectivity curve of the second layer system (shown in dashed lines) is in turn in the opposite direction to the reflectivity curve of the first layer system (shown in solid lines).

[0040] To illustrate a concrete embodiment, Table 1 shows a possible layer design for a first layer system, and Table 2 shows a suitable layer design of a second layer system suitable for achieving the desired compensation effect. Table 1: material Layer thickness [λ / 4] LaF3 1 MgF2 1 LaF3 1 MgF2 1 LaF3 1 Table 2: material Layer thickness [λ / 4] LaF3 1.82 MgF2 1.54 LaF3 1.69 MgF2 0.99 LaF3 1.01 MgF2 1.85 LaF3 1.05 MgF2 1.02 LaF3 0.99

[0041] Fig. Figure 5 shows the corresponding wavelength-dependent reflectivity curves, where for the second layer system both the desired curve for an ideal compensation effect and the actual curve actually achieved with the specific layer design are shown. Fig. As can be seen in Figure 5, the resulting total reflectivity exhibits a largely plateau-like curve over a comparatively broad wavelength range from approximately 160 nm to 240 nm.

[0042] As a further concrete embodiment, Table 3 shows another possible layer design of a first layer system, and Table 4 shows a layer design of a correspondingly coordinated second layer system suitable for achieving the compensation effect according to the invention. Table 3: material Layer thickness [λ / 4] LaF3 1 MgF2 2 LaF3 1 MgF2 1 LaF3 1 MgF2 1 LaF3 1.1 Table 4: material Layer thickness [λ / 4] LaF3 0.31 MgF2 1.25 LaF3 1.02 MgF2 1.99 LaF3 0.99 MgF2 1.68 LaF3 1.43

[0043] Fig. 6 shows in to Fig. 5 analogously shows the respective wavelength-dependent reflectivity curves for the embodiment from Table 3 to Table 4.

[0044] The invention is not limited to the implementation with two coordinated layer systems on an optical component. Fig.7 shows, in a merely schematic representation, an optical component 700 composed of two subcomponents 701, 702, wherein subcomponent 701 is again an optical beam splitter and subcomponent 702 is a mirror. Thus, a total of three optically effective surfaces or layer systems 710, 720, 730 present on these surfaces are available for component 700, which can be coordinated with one another with regard to their respective wavelength-dependent reflectivity profiles to achieve the compensation effect according to the invention.

[0045] Fig.8 shows, as a further application example, an optical component 800 with three optically effective surfaces or layer systems 810, 820, 830 located thereon. The optical component 800 acts either as a deflecting mirror (for the portion reflected by the layer system 830 and transmitted through the layer system 820) or as an output coupling element (for the portion transmitted through the layer system 830). Depending on the specific application scenario, the layer systems 820 and 830, for example, can be matched to one another according to the invention in such a way that the ratio of the portions transmitted there remains constant over a sufficiently broad wavelength range.

[0046] Fig.Figure 9 shows a schematic representation of another example of an optical component 900, which is composed of two subcomponents 901, 902, each in the form of beam splitters. To achieve the compensation effect according to the invention, a total of four optically effective surfaces or layer systems 910, 920, 930, and 940 located thereon are thus available.

[0047] Fig. 10 shows, as a further possible application example, an optical component 1000 in the form of a deflection or coupling-out element, wherein three different optical surfaces or layer systems 1010, 1020, 1030 located thereon are present, of which, however, the layer system 1010 is traversed twice according to the indicated beam path. As in Fig.As indicated in Figure 10, two different partial beams (corresponding to the portion transmitted through layer system 1020 and the portion transmitted through layer system 1030) can be coupled out with the optical component 1000. Furthermore, depending on the specific application scenario, all three layer systems or just two of these layer systems can be coordinated with one another in the manner according to the invention with regard to their wavelength-dependent reflectivity profile.

[0048] Fig. 11 shows a fundamentally possible structure of a microlithographic projection exposure system 1100 designed for operation in DUV.

[0049] The projection exposure system 1100 according to Fig.11 has an illumination device 1110 and a projection lens 1120. The illumination device 1110 serves to illuminate a structure-bearing 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 also in the form of a KrF excimer laser for an operating wavelength of 248 nm), as well as beam-shaping optics generating a parallel light beam. The laser light source can be configured in the manner according to the invention.

[0050] The illumination device 1110 has an optical unit 1111, which, in the example shown, includes a deflection mirror 1112. The optical unit 1111 can, for example, have a diffractive optical element (DOE) and a zoom axicon system to generate different illumination settings (i.e., intensity distributions in a pupil plane of the illumination device 1110). In the light propagation direction downstream of the optical unit 1111, a light mixing device (not shown) is located in the beam path, which, for example,in a manner known per se, an arrangement of micro-optical elements suitable for achieving light mixing, as well as a lens group 1113, behind which there is a field plane with a reticle masking system (REMA), which is imaged by a REMA objective 1114 following in the direction of light propagation onto the structure-bearing mask (reticle) 1115 arranged in a further field plane, thereby delimiting the illuminated area on the reticle. The structure-bearing mask 1115 is imaged by the projection objective 1120 onto a substrate or wafer 1130 provided with a light-sensitive layer (photoresist). The projection objective 1120 can be designed in particular for immersion operation, in which case an immersion medium is located in front of the wafer or its light-sensitive layer with respect to the direction of light propagation.Furthermore, it may, for example, have a numerical aperture NA greater than 0.85, in particular greater than 1.1.

[0051] In Fig. Figure 12a merely schematically shows a laser 1210 with a beam splitter 1211 inserted therein as an exemplary application of the present invention. Beam splitters can be used, for example, in an optical pulse stretcher or for coupling out a partial beam, for example for beam measurement. Fig. 12b also shows only schematically a microscope 1220 (e.g. for wafer inspection) with a beam splitter 1221 inserted therein as a further exemplary application of the invention.

Claims

[1] Optical component, with: • a first layer system (210, 710, 810, 910, 1010) which, when exposed to electromagnetic radiation, has a first wavelength-dependent reflectivity profile; and • at least one second layer system (220, 720, 820, 920, 1020) which, when exposed to electromagnetic radiation, has a second wavelength-dependent reflectivity profile; • wherein the first layer system (210, 710, 810, 910, 1010) and the second layer system (220, 720, 820, 920, 1020) are arranged on different optical surfaces; and • wherein the wavelength dependencies of the first and second reflectivity curves at least partially compensate each other such that for a total reflectivity resulting for the first layer system (210, 710, 810, 910, 1010) and the at least one second layer system (220, 720, 820, 920, 1020) in the predetermined wavelength range, the relative deviation from a desired reflectivity curve that is linear or constant with respect to the wavelength is a maximum of 5%; and • wherein the optical component comprises at least one beam splitter. [2] Optical component according to claim 1, characterized bythat the wavelength dependencies of the first and the second reflectivity curves at least partially compensate for one another in such a way that for a total reflectivity resulting for the first layer system (210, 710, 810, 910, 1010) and the at least one second layer system (220, 720, 820, 920, 1020) in the predetermined wavelength range, the relative deviation from a desired reflectivity curve that is linear or constant with respect to the wavelength is a maximum of 3%, preferably a maximum of 2%. [3] Optical component according to claim 1 or 2, characterized by that a total reflectivity resulting for the first layer system (210, 710, 810, 910, 1010) and the at least one second layer system (220, 720, 820, 920, 1020) is constant in the predetermined wavelength range up to a maximum relative variation of 5%, preferably of 3% and particularly preferably of 2%. [4] Optical component according to one of claims 1 to 3, characterized by that for the resulting reflectivity curve, a maximum variation of the reflectivity in the predetermined wavelength range is smaller than the respective maximum variation of the reflectivity in the predetermined wavelength range for the first wavelength-dependent reflectivity curve and for the second wavelength-dependent reflectivity curve. [5] Optical component according to one of the preceding claims, characterized by in that in the first reflectivity profile of the first layer system (210, 710, 810, 910, 1010) the reflectivity varies as a function of the wavelength in the predetermined wavelength range by at least 5%, preferably by at least 10%, based on the maximum reflectivity. [6] Optical component according to one of the preceding claims, characterized by that it further comprises at least one third layer system (730, 830, 930, 1030) with a third wavelength-dependent reflectivity profile. [7] Optical component according to claim 6, characterized by that for a total reflectivity resulting for the first layer system (710, 810, 910, 1010), the second layer system (720, 820, 920, 1020) and the third layer system (730, 830, 930, 1030) in the predetermined wavelength range, the relative deviation from a desired linear reflectivity curve is a maximum of 5%, preferably a maximum of 3% and particularly preferably a maximum of 2%. [8] Optical component according to one of the preceding claims, characterized by that the predetermined wavelength range for a predetermined working wavelength λ0 extends from 0.95*λ0 to 1.05*λ0, preferably from 0.9*λ0 to 1.1*λ0, particularly preferably from 0.8*λ0 to 1.2*λ0 and very particularly preferably from 0.7*λ0 to 1.3*λ0. [9] Optical component according to one of the preceding claims, characterized bythat it has a decoupling element for decoupling a partial beam from the optical beam path of an optical system. [10] Optical component according to one of the preceding claims, characterized by that it has a deflection element for deflecting a partial beam in the optical beam path of an optical system. [11] Optical component according to one of the preceding claims, characterized by that it is designed for an operating wavelength in the range of 100 nm to 700 nm. [12] An optical system comprising an optical component according to any one of the preceding claims. [13] Optical system according to claim 12, characterized by that the optical system is designed for microlithography. [14] Optical system according to claim 12 or 13, characterized by that the optical component is arranged in a laser light source.

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