OPTICAL COMPONENT AND OPTICAL SYSTEM, IN PARTICULAR FOR MICROLITHOGRAPHY

Abstract

An optical component comprises a first layer system exhibiting a first wavelength-dependent reflectivity curve when electromagnetic radiation impinges thereon, and at least one second layer system exhibiting a second wavelength-dependent reflectivity curve when electromagnetic radiation impinges thereon. The first layer system and the second layer system are arranged on different optical surfaces. The wavelength dependencies of the first and the second reflectivity curve at least partially compensate one another so that the relative deviation from a desired reflectivity curve which is linear or constant with respect to the wavelength is no more than 5% within the specified wavelength range for a resultant summated reflectivity for the first layer system and the at least one second layer system. An optical system, such as a microlithography projection exposure apparatus, can include such an optical component.

Claims

1. An optical component having optical surfaces, the optical component comprising: a first layer system configured to exhibit a first wavelength-dependent reflectivity curve when electromagnetic radiation impinges thereon; and a second layer system configured to exhibit a second wavelength-dependent reflectivity curve when electromagnetic radiation impinges thereon, wherein: the first layer system and the second layer system are on different optical surfaces; within a predetermined wavelength range, a dependency of the first reflectivity curve and a dependency of the second reflectivity curve at least partially compensate one another so that a relative deviation from a predetermined reflectivity curve is no more than 5% for a resultant summated reflectivity for the first layer system and the second layer system; and the predetermined reflectivity curve is linear or constant with respect to wavelength.

2. The optical component of claim 1, wherein, within the predetermined wavelength range, the wavelength dependencies of the first reflectivity curve and the second reflectivity curve at least partially compensate one another so that the relative deviation from the predetermined reflectivity curve is no more than 3% for the resultant summated reflectivity for the first layer system and the second layer system.

3. The optical component of claim 1, wherein, within the specified wavelength range, the resultant summated reflectivity for the first layer system and the second layer system is constant apart from a maximum relative variation of 5%.

4. The optical component of claim 1, wherein, within the specified wavelength range, a maximum variation of a reflectivity for a resultant reflectivity curve is less than a respective maximum variation of the reflectivity for the first wavelength-dependent reflectivity curve and for the second wavelength-dependent reflectivity curve.

5. The optical component of claim 1, wherein, within the specified wavelength range, a reflectivity of the first wavelength-dependent reflectivity curve varies by at least 5% relative to a maximum reflectivity of the first wavelength-dependent reflectivity curve.

6. The optical component of claim 1, wherein the optical component further comprises a third layer system having a third wavelength-dependent reflectivity curve.

7. The optical component of claim 6, wherein, within the specified wavelength range, a resultant summated reflectivity for the first, second and third layer systems deviates by no more than 5% relative to a linear reflectivity curve.

8. The optical component of claim 1, wherein the specified wavelength range extends for a given operating wavelength λ.sub.0 from 0.95*λ.sub.0 to 1.05*λ.sub.0.

9. The optical component of claim 1, wherein the optical component comprises a beam splitter.

10. The optical component of claim 1, wherein the optical component comprises an output coupling element configured to output couple a component beam from an optical beam path of an optical system.

11. The optical component of claim 1, wherein the optical component comprises a deflection element configured to deflect a component beam in an optical beam path of an optical system.

12. The optical component of claim 1, wherein the optical component is configured to be used in an operating wavelength ranging from 100 nm to 700 nm.

13. An optical system, comprising: an optical component according to claim 1, wherein the optical system is a microlithography optical system.

14. An optical component having first and second optical surfaces, the optical component comprising: a first layer system configured to exhibit a first wavelength-dependent reflectivity curve when electromagnetic radiation impinges thereon; and a second layer system configured to exhibit a second wavelength-dependent reflectivity curve when electromagnetic radiation impinges thereon, wherein: the first layer system is supported by the first optical surface; the second layer system is supported by the second optical surface; within a predetermined wavelength range, the first and second wavelength-dependent reflectivity curves at least partially compensate each other so that a relative deviation from a predetermined reflectivity curve is no more than 5% for a summated reflectivity for the first and second layer systems; and the predetermined reflectivity curve is linear or constant with respect to wavelength.

15. The optical component of claim 14, wherein, within the predetermined wavelength range, the first and second wavelength-dependent reflectivity curves at least partially compensate each other so that the relative deviation from the predetermined reflectivity curve is no more than 3% for the summated reflectivity for the first and second layer systems.

16. The optical component of claim 14, wherein, within the specified wavelength range, the resultant summated reflectivity for the first and second layer systems has a maximum relative variation of at most 5% from being constant.

17. The optical component of claim 14, wherein, within the specified wavelength range: a resultant reflectivity curve is a sum of the first and second wavelength-dependent reflectivity curves; a maximum variation of a reflectivity for the resultant reflectivity curve is less than a maximum variation of a reflectivity for the first wavelength-dependent reflectivity curve; and the maximum variation of a reflectivity for the resultant reflectivity curve is less than a maximum variation of a reflectivity for the second wavelength-dependent reflectivity curve.

18. The optical component of claim 14, wherein, within the specified wavelength range, a reflectivity of the first wavelength-dependent reflectivity curve varies by at least 5% from a maximum reflectivity of the first wavelength-dependent reflectivity curve.

19. The optical component of claim 14, wherein: the optical component further comprises a third layer system having a third wavelength-dependent reflectivity curve; and within the specified wavelength range, a resultant summated reflectivity for the first, second and third layer systems deviates by no more than 5% from a linear reflectivity curve.

20. An optical system, comprising: an optical component according to claim 14, wherein the optical system is a microlithography optical system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the figures:

[0035] FIG. 1 shows a diagram for explaining a concept underlying the present disclosure;

[0036] FIG. 2 shows a schematic illustration of the basic possible structure of a beam splitter in which the present disclosure can be realized;

[0037] FIGS. 3A-6 show diagrams for explaining possible embodiments of the present disclosure;

[0038] FIGS. 7-10 show schematic illustrations of exemplary optical components in which the present disclosure can be realized;

[0039] FIG. 11 shows a schematic illustration for explaining the possible structure of a microlithographic projection exposure apparatus designed for operation in the DUV;

[0040] FIGS. 12A-12B show schematic illustrations of exemplary applications of the disclosure; and

[0041] FIG. 13 shows a diagram for explaining a problem occurring in accordance with the prior art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] Embodiments of the present disclosure are explained hereinafter with reference to the diagrams in FIGS. 3A-6 and also the schematic illustrations in FIG. 2 and FIGS. 7-20 10.

[0043] What is common to the embodiments described hereinafter is that—in view of the object of avoiding a change in the optical performance occurring due to a degradation during operation of an optical component or an optical system comprising this component—at least two layer systems situated on different surfaces of the relevant optical component are matched to one another in terms of their respective wavelength-dependent reflectivity behaviour so that, in respect of the effects of a degradation or structural change, an at least partial compensation effect and, overall, a largely constant reflectivity behaviour of the optical component are obtained.

[0044] In so doing, the present disclosure for example proceeds from the idea that—as already explained at the outset on the basis of the diagram in FIG. 13—a degradation in the material of an optical component such as a beam splitter, for example, ultimately corresponds in terms of its effect on the reflection behaviour of the optical component to a shift of the effective wavelength which, without suitable countermeasures, is accompanied by an impairment of the performance of the relevant optical component (which of course was initially constructed in a targeted manner for the specific operating wavelength of the respective optical system). According to the disclosure, an allowance is made for these circumstances by virtue of a substantially plateau-shaped wavelength-dependent reflectivity curve for the component overall being sought after for the relevant optical component even over a relatively large wavelength range—despite its intended use only for a specific operating wavelength (of 193 nm, for example)—since, as indicated in FIG. 1, a consequence of this plateau-shaped curve is that the aforementioned degradation-related shift of the effective wavelength no longer leads to an impairment in the optical reflection behaviour.

[0045] As described below on the basis of various embodiments with reference to FIG. 2 to FIG. 10, the substantially constant performance of the optical component in view of the reflection behaviour is achieved overall according to the disclosure by virtue of at least two layer systems situated on different surfaces of the optical component having in a certain sense opposing wavelength-dependent reflectivity curves and consequently being “pitted against one another” in respect of their respective degradation effect or being matched to one another within the meaning of a mutual compensation.

[0046] For example (but without the disclosure being restricted thereto), the concept according to the disclosure can be realized in an optical component in the form of an optical beam splitter, for example as is used in a laser light source or in other optical systems, especially for microlithography. According to the purely schematic illustration in FIG. 2, such a beam splitter 200 can be constructed from a first layer system 210 and a second layer system 220, with FIG. 2 further indicating, for an incident light beam with the intensity I.sub.0, the occurrence of both a reflected intensity component I.sub.R and a transmitted intensity component I.sub.T. Both the overall reflectivity resulting for the beam splitter 200 and the corresponding overall transmissivity are composed of the respective properties of the two layer systems 210, 220, with the overall reflectivity arising as

[00001]$\begin{array}{cc}{R}_{\mathrm{overall}}=r_1+\frac{{\left(1-r_1\right)}^2{r}_2}{1-r_1{r}_2}& \left(1\right)\end{array}$

if optical losses are neglected. In this case, r.sub.1 and r.sub.2 denote the respective partial reflectivities of the first and the second layer system 210, 220.

[0047] For the exemplary realization of the concept according to the disclosure, FIG. 3A now 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 suitable according to the disclosure for obtaining the desired compensation effect. As is evident from FIGS. 3A-3B, significant variations of the individual wavelength-dependent reflectivity curves are definitely “allowed” in the process, with however these wavelength-dependent variations (including the intermediate extremals present in the specific example) running precisely counter or complementary to one another.

[0048] FIG. 4 shows a further example for the matching to one another according to the disclosure of two layer systems of an optical component such as an optical beam splitter, for example, with the reflectivity curve (illustrated using dashed lines) of the second layer system once again running precisely counter to the reflectivity curve (illustrated using a solid line) of the first layer system.

[0049] To illustrate a specific exemplary 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 obtaining the desired compensation effect.

TABLE-US-00001 TABLE 1 Layer thickness Material [λ/4] LaF.sub.3 1 MgF.sub.2 1 LaF.sub.3 1 MgF.sub.2 1 LaF.sub.3 1

TABLE-US-00002 TABLE 2 Layer thickness Material [λ/4] LaF.sub.3 1.82 MgF.sub.2 1.54 LaF.sub.3 1.69 MgF.sub.2 0.99 LaF.sub.3 1.01 MgF.sub.2 1.85 LaF.sub.3 1.05 MgF.sub.2 1.02 LaF.sub.3 0.99

[0050] In this respect, FIG. 5 shows the corresponding wavelength-dependent reflectivity curves, with both the desired target profile for an ideal compensation effect and the actual profile in fact realized by the specific layer design being illustrated for the second layer system. As is evident from FIG. 5, a largely plateau-shaped curve over a comparatively broad wavelength range from approximately 160 nm to 240 nm is achieved for the resultant overall reflectivity.

[0051] As a further specific exemplary embodiment, Table 3 shows a further possible layer design of a first layer system, and Table 4 shows a layer design of a correspondingly matched second layer system suitable for obtaining the compensation effect according to the disclosure.

TABLE-US-00003 TABLE 3 Layer thickness Material [λ/4] LaF.sub.3 1 MgF.sub.2 2 LaF.sub.3 1 MgF.sub.2 1 LaF.sub.3 1 MgF.sub.2 1 LaF.sub.3 1.1

TABLE-US-00004 TABLE 4 Layer thickness Material [λ/4] LaF.sub.3 0.31 MgF.sub.2 1.25 LaF.sub.3 1.02 MgF.sub.2 1.99 LaF.sub.3 0.99 MgF.sub.2 1.68 LaF.sub.3 1.43

[0052] In a manner analogous to FIG. 5, FIG. 6 shows the respective wavelength-dependent reflectivity curves for the exemplary embodiment of Table 3 to Table 4.

[0053] The disclosure is not restricted to the realization with two mutually matched layer systems on an optical component. FIG. 7 shows, only in a schematic illustration, an optical component 700 made up of two partial components 701, 702, with the partial component 701 yet again being an optical beam splitter and the partial component 702 being a mirror. Consequently, a total of three optically effective surfaces or layer systems 710, 720, 730 present at these surfaces are available for the component 700, which surfaces or layer systems can be matched to one another in respect of their respective wavelength-dependent reflectivity curves for the purpose of obtaining the compensation effect according to the disclosure.

[0054] FIG. 8 shows, as a further application example, an optical component 800 with three optically effective surfaces or layer systems 810, 820, 830 situated thereon. In this case, the optical component 800 selectively acts as a deflection mirror (for the portion reflected at 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). In this case, depending on the specific use scenario, the layer systems 820 and 830, for example, can be matched to one another according to the disclosure in such a way that the ratio of the portions transmitted there in each case remains constant over a sufficiently broad wavelength range.

[0055] In a schematic illustration, FIG. 9 shows a further example of an optical component 900 which is made up of two partial components 901, 902, each in the form of a beam splitter. Consequently, a total of four optically effective surfaces or layer systems 910, 920, 930 and 940 situated thereon are available for the purpose of obtaining the compensation effect according to the disclosure.

[0056] As a further possible exemplary application, FIG. 10 shows an optical component 1000 in the form of a deflection or output coupling element, wherein three different optical surfaces or layer systems 1010, 1020, 1030 situated thereon are available, of which however the layer system 1010 is passed through twice in accordance with the indicated beam path. As indicated in FIG. 10, the optical component 1000 can be used to output couple two different component beams (corresponding to the portion transmitted through the layer system 1020 and the portion transmitted through the layer system 1030). Moreover, depending on the specific use scenario, all three layer systems or else only two of these layer systems can be matched to one another, in the manner according to the disclosure, in respect of their wavelength-dependent reflectivity curve.

[0057] FIG. 11 shows a structure, possible in principle, of a microlithographic projection exposure apparatus 1100 designed for operation in the DUV.

[0058] The projection exposure apparatus 1100 in accordance with FIG. 11 comprises an illumination device 1110 and a projection lens 1120. The illumination device 1110 serves for illuminating a structure-bearing mask (reticle) 1115 with light from a light source unit 1105 comprising 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 also a beam shaping optical unit that generates a parallel light beam. In this case, the laser light source can be designed in the manner according to the disclosure.

[0059] The illumination device 1110 comprises an optical unit 1111 which, inter alia, comprises a deflection mirror 1112 in the example illustrated. The optical unit 1111 can comprise for example a diffractive optical element (DOE) and a zoom-axicon system for producing different illumination settings (i.e., intensity distributions in a pupil plane of the illumination device 1110). A light mixing device (not illustrated) is situated in the beam path downstream of the optical unit 1111 in the light propagation direction, which light mixing device can have for example, in a manner known per se, an arrangement composed of micro-optical elements which is suitable for attaining light mixing, and a lens-element group 1113, downstream of which there is a field plane with a reticle masking system (REMA), which is imaged by a REMA lens 1114, disposed downstream in the light propagation direction, onto the structure-bearing mask (reticle) 1115 arranged in a further field plane and which thereby delimits the illuminated region on the reticle. Via the projection lens 1120, the structure-bearing mask 1115 is imaged onto a substrate provided with a light-sensitive layer (photoresist) or onto a wafer 1130. For example, the projection lens 1120 can be designed for immersion operation, in which case an immersion medium is situated upstream of the wafer, or the light-sensitive layer thereof, in relation to the light propagation direction. Furthermore, it can have for example a numerical aperture NA greater than 0.85, for example greater than 1.1.

[0060] FIG. 12A indicates, purely schematically, a laser 1210 having a beam splitter 1211 inserted therein as an exemplary application of the present disclosure. By way of example, beam splitters may also be used in an optical pulse stretcher or else for the purpose of output coupling a component beam, for example for beam measurement purposes. FIG. 12B indicates, likewise purely schematically, a microscope 1220 (e.g., for wafer inspection) having a beam splitter 1221 inserted therein as a further exemplary application of the disclosure.

[0061] Even though the disclosure has also been described on the basis of specific embodiments, numerous variations and alternative embodiments will be apparent to a person skilled in the art, for example by the combination and/or exchange of features of individual embodiments. Accordingly, it goes without saying for a person skilled in the art that such variations and alternative embodiments are concomitantly encompassed by the present disclosure, and the scope of the disclosure is restricted only within the meaning of the appended patent claims and the equivalents thereof.