Abstract
A heating arrangement, for example for use in a microlithographic projection exposure apparatus, comprises: at least one beam shaping unit for beam shaping of the electromagnetic radiation steered from a radiation source to the at least one optical element; and a sensor arrangement having at least one intensity sensor. The at least one beam shaping unit comprises at least one microstructured element for steering some the electromagnetic radiation to the sensor arrangement when the heating arrangement is in operation. Methods are provided.
Claims
1. A heating arrangement, comprising: a beam shaping unit configured to shape a beam of electromagnetic radiation travelling from a radiation source to an optical element; and an intensity sensor, wherein the beam shaping unit comprises a microstructured element configured to steer some of the electromagnetic radiation to the intensity sensor.
2. The heating arrangement of claim 1, wherein the microstructured element comprises a diffractive optical element.
3. The heating arrangement of claim 1, wherein the microstructured element comprises a refractive optical element.
4. The heating arrangement of claim 1, wherein the beam shaping unit comprises a plurality of separate regions configured to incident electromagnetic radiation in directions that differ from one another.
5. The heating arrangement of claim 4, wherein the heating arrangement comprises a plurality of intensity sensors.
6. The heating arrangement of claim 5, wherein the separate regions of the beam shaping unit deflect electromagnetic radiation to intensity sensors that differ from one another.
7. The heating arrangement of claim 1, wherein the heating arrangement comprises a plurality of intensity sensors.
8. The heating arrangement of claim 1, further comprising a further beam shaping units configured to shape a beam of the electromagnetic radiation travelling from the radiation source to a further optical element.
9. The heating arrangement of claim 1, further comprising a driving unit configured to drive the radiation source based information from the intensity sensor.
10. The heating arrangement of claim 9, further comprising a control unit configured to control a power of the radiation source based on information from the intensity sensor.
11. The heating arrangement of claim 1, further comprising a control unit configured to control a power of the radiation source based on information from the intensity sensor.
12. The heating arrangement of claim 1, wherein the optical element comprises a mirror.
13. The heating arrangement of claim 1, wherein the electromagnetic radiation has a wavelength of less than 30 nm.
14. An optical system, comprising: an optical element; and a heating arrangement, comprising: a beam shaping unit configured to shape a beam of electromagnetic radiation travelling from a radiation source to the optical element; and an intensity sensor, wherein the beam shaping unit comprises a microstructured element configured to steer some of the electromagnetic radiation to the intensity sensor.
15. The optical system of claim 14, wherein the optical system is a microlithographic projection exposure apparatus.
16. The optical system of claim 15, wherein the electromagnetic radiation has a wavelength of less than 30 nm.
17. A method, comprising: using a beam shaping unit to direct a first portion of electromagnetic radiation to an optical element, the beam shaping unit comprising a microstructured element; and using the microstructured element to direct a second portion of the electromagnetic radiation to an intensity sensor.
18. The method of claim 17, further comprising controlling a power of the radiation source based on information from the intensity sensor.
19. The method of claim 17, further comprising adjusting the method based on information from the intensity sensor.
20. The method of claim 17, comprising heating the optical element to reduce a spatial and/or temporal variation of a temperature distribution in the optical element.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIGS. 1-5 show schematic representations for explaining basic possible embodiments of a heating arrangement according to the disclosure;
[0041] FIGS. 6A-6E show schematic representations for explaining structure and functionality of a specific design of a heating arrangement in an embodiment of the disclosure;
[0042] FIG. 7 shows a schematic representation for explaining structure and functionality of a specific design of a heating arrangement in a further embodiment of the disclosure;
[0043] FIGS. 8A-8D show schematic representations for explaining a further design and application of a heating arrangement according to the disclosure; and
[0044] FIG. 9 shows a schematic representation of the possible structure of a microlithographic projection exposure apparatus designed for operation in the EUV.
DETAILED DESCRIPTION
[0045] FIG. 9 firstly shows a schematic representation of a projection exposure apparatus 900 which is designed for operation in the EUV and in which the disclosure is able to be realized in an exemplary manner.
[0046] According to FIG. 9, an illumination device of the projection exposure apparatus 900 comprises a field facet mirror 903 and a pupil facet mirror 904. The light from a light source unit comprising an EUV light source (plasma light source) 901 and a collector mirror 902 in the example is directed onto the field facet mirror 903. A first telescope mirror 905 and a second telescope mirror 906 are arranged in the light path downstream of the pupil facet mirror 904. A deflection mirror 907 is arranged downstream in the light path, the deflection mirror steering the radiation that is incident thereon at an object field in the object plane of a projection lens comprising six mirrors 921-926. At the location of the object field, a reflective structure-bearing mask 931 is arranged on a mask stage 930, the mask being imaged with the aid of the projection lens into an image plane in which a substrate 941 coated with a light-sensitive layer (photoresist) is situated on a wafer stage 940.
[0047] During operation of the optical system or microlithographic projection exposure apparatus, the electromagnetic radiation incident on the optical effective surface of the mirrors is partly absorbed and, as explained in the introduction, results in heating and an associated thermal expansion or deformation, which can in turn result in an impairment of the imaging properties of the optical system. The heating arrangement according to the disclosure or method for heating an optical element can be applied for example to any desired mirror of the microlithographic projection exposure apparatus of FIG. 9.
[0048] Further, possible designs of a heating arrangement according to the disclosure are initially explained with reference to FIG. 1-5, whereupon specific designs in exemplary embodiments of the disclosure are described on the basis of FIG. 6A-6E and FIG. 7.
[0049] What is common to these designs or specific embodiments of a heating arrangement is the use of a beam shaping unit, in particular in the form of at least one diffractive optical element, and the use of this beam shaping unit, inter alia for the purpose of steering some of the electromagnetic radiation to one or more predefined positions in angular space, where then the information for monitoring the function and optionally for further tasks (for instance, driving or controlling the radiation source and/or position monitoring or adjustment) is acquired by way of a sensor arrangement comprising at least one intensity sensor.
[0050] FIG. 1 shows in a schematic and very much simplified representation a beam shaping unit 12 which is situated within an optical system 11 and has the form of a diffractive optical element (DOE) which partially steers electromagnetic radiation entering the optical system 11 that forms the heating arrangement and being incident on the DOE to a sensor arrangement in the form of an intensity sensor 13. The remaining (heating) radiation that is not steered to the intensity sensor 13 emerges from the heating arrangement 11 and serves to impinge on an optical element (not depicted in FIG. 1 but indicated in FIG. 2, for example), for example in the form of an EUV mirror. According to the schematic example of FIG. 1, the intensity sensor 13 that forms the sensor arrangement is situated within the optical system 11.
[0051] FIG. 2 likewise shows a further fundamentally possible design in a schematic and much simplified manner, with components that are analogous or substantially functionally identical in comparison with FIG. 1 being designated by reference numerals increased by 10. In contrast to FIG. 1, the intensity sensor 23 that forms the sensor arrangement is outside of the optical system 21 according to FIG. 2. The optical element to be heated is indicated using 25.
[0052] FIG. 3 shows, once again in a schematic and much simplified manner, a further possible basic design, with in contrast to FIG. 2 a DOE that forms the beam shaping unit 32 having two separate regions 32a, 32b, which partly steer electromagnetic (heating) radiation to intensity sensors 33a, 33b that form the sensor arrangement and differ from one another.
[0053] FIG. 4 shows a representation analogous to FIG. 3, with components which are analogous or substantially functionally identical to FIG. 3 being denoted by reference numeral increased by 10. In contrast to FIG. 3, the separate regions 42a, 42b of the DOE that form the beam shaping unit 42 steer electromagnetic radiation to one and the same intensity sensor 43 according to FIG. 4.
[0054] FIG. 5 shows a schematic and much simplified representation for the purposes of explaining a further possible design. According to FIG. 5, the heating arrangement has two separate optical systems 51a, 51b for impinging on separate optical elements 55a, 55b, with each of these optical systems 51a, 51b having a respective design analogous to FIG. 4. In this case, the radiation steered in the direction of the sensor arrangement by the separate regions 52a, 52b and 54a, 54b, respectively, of the DOE forming the respective beam shaping unit 52 or 54 is incident on one and the same intensity sensor 53.
[0055] FIG. 6A-6E show schematic representations for explaining structure and functionality of a specific design of a heating arrangement in an embodiment of the disclosure.
[0056] According to FIG. 6A, the heating arrangement according to the disclosure comprises in particular a plurality of emitters 601, 602, 603, 604, which may also be present in greater or smaller number. By way of example, the emitters 601, 602, 603, 604 can be designed as IR lasers or IR LEDs (without the disclosure being restricted thereto). According to FIG. 6A, the electromagnetic radiation generated by the emitters 601-604 strikes a beam shaping unit denoted by 630 via a microlens array 620optionally provided to generate a collimated beam pathand, from the beam shaping unit, the electromagnetic radiation strikes the optical effective surface of an optical element or mirror (not depicted in FIG. 6A).
[0057] The beam shaping unit 630 comprises at least one microstructured element, in particular a diffractive optical element (DOE) or refractive optical element (ROE). In embodiments, the beam shaping unit 630 may also have a plurality of beam shaping segments, with each of these beam shaping segments being able to be assigned to a respective emitter 601-604. These beam shaping segments bring about both beam shaping and a beam deflection with respect to the electromagnetic (heating) radiation that is to be steered to the optical effective surface of the optical element to be heated.
[0058] As indicated in FIG. 6A and FIG. 6B, the DOE that forms the beam shaping unit 630 has separate regions 631, 632, 633, 634, . . . that are spatially separated from one another. According to FIG. 6C, each of the separate regions generates a first defined angle distribution 641, 642, 643 or 644 of the electromagnetic radiation in angular space, with the angle distributions being able to differ from one another for the separate regions. Moreover, according to FIG. 6D, each of the separate regions respectively generates a second defined angle distribution 651, 652, 653 or 654 of the electromagnetic radiation in angular space, with these second angle distributions also being able to differ from one another for the separate regions. The aforementioned first and second angle distributions may irradiate corresponding or else separated regions in real space, with these regions fundamentally being able to be of any desired form according to FIG. 6E (where regions 661, 671, 664 and 674 are sketched out in exemplary fashion) and also being able to overlap one another.
[0059] FIG. 7 shows a schematic representation for explaining structure and functionality of a specific design of a heating arrangement in a further embodiment of the disclosure.
[0060] According to FIG. 7, a beam generated by a radiation source (not depicted), which can be purely in exemplary fashion a fibre laser for generating IR radiation at a wavelength of for example 1070 nm, emerges at a fibre end designated by 701 and firstly passes through an optical collimator 705, which according to FIG. 7 is constructed purely in exemplary fashion from lenses 706, 707. The collimated beam emerging from the collimator 705 enters an optical component 710. In embodiments, the fibre end 701 may be adjustable both laterally (i.e., within the xy-plane in relation to the coordinate system plotted in the region of the fibre end 701) and axially (i.e., in the z-direction in relation to this coordinate system) in this case.
[0061] A function of the optical component 710 (which comprises a beam splitter 711 and a deflection mirror 712 according to FIG. 7) is to provide two partial beams, each of which is linearly polarized, from the laser beam originally still unpolarized upon entering the component 710, with the linearly polarized partial beams being able to be used for input couplingoptimized with regard to absorptionof heating radiation into the optical element to be heated in each case (e.g., an EUV mirror of the microlithographic projection exposure apparatus from FIG. 9). Such a generation of two partial beams, each of which is linearly polarized, by way of the optical component 710 is advantageous in that a sufficient absorption of the heating radiation can be achieved even when input coupling the generated heating radiation at comparatively large angles of incidence in relation to the respective surface normal (what is known as a grazing incidence). Such input coupling of the heating radiation with grazing incidence in turn may prove to be desirable in the concrete application situation with respect to structural space aspects ifas is often the casesufficient structural space is not available within the projection exposure apparatus in the direction perpendicular to the surface of the optical element to be heated. Furthermore, the input coupling of the heating radiation with grazing incidence, depending on the concrete application situation, makes it possible optionally to ensure that the heating arrangement is arranged outside the actual used beam path. Further, input coupling at a grazing incidence makes it possible for the heating radiation to leave the relevant EUV mirror at a correspondingly large angle and not be steered directly to an immediately adjacent mirror. Moreover, the occurrence of reflected IR radiation at the EUV mirror can be reduced in the case of a suitable polarization.
[0062] According to FIG. 7, the partial beams each having linear polarization emerge from the optical component 710 along the original light propagation direction along two separate parallel beam paths and each successively pass through an optical retarder 721 and 731, respectively, a diffractive optical element (DOE) 722 and 732, respectively, and an optical telescope 723 and 733, respectively. A suitable setting of the respective polarization direction can be achieved by way of the optical retarders 721 and 731 (which may be designed as lambda/2 plates, for example). The DOEs 722 and 732 serve inter alia as beam shaping units for impressing an individual heating profile into the optical element to be heated by way of beam shaping of the IR radiation to be steered onto the optical effective surface of the optical element. In this case, at least one of the two DOEs 722 and 732 may be arranged in embodiments as to be rotatable about the respective element axis for adjustment purposes, as indicated in exemplary fashion for the element 732. According to FIG. 7, the optical telescopes 723 and 733 are constructed from lenses 724-726 and 734-736, respectively, purely in exemplary fashion. In embodiments, the respective last lens 726 or 736 in the beam path in one of the telescopes 722, 733 or else in both telescopes 722, 733 may be adjustable by way of a lateral displacement (i.e., within the xy-plane in relation to the coordinate system plotted in the region of the lenses 726, 736). The optical telescopes 723 and 733 serve the provision of a suitable additional beam deflection prior to the input coupling of the electromagnetic (heating) radiation into the optical element to be heated or into the EUV mirror.
[0063] In the embodiment according to FIG. 7, the DOEs 722 and 732 steer incident electromagnetic (heating) radiation in a manner analogous to the embodiments described above, but in this case in combination with the telescopes 723 and 733 downstream in the optical beam path, to defined positions in angular space, with the corresponding distribution of the radiation in angular and real space brought about by the telescopes 723 and 733 corresponding or else being able to differ from one another. Moreover, each DOE 722 and 732 may have a single region (as depicted in FIG. 7) or elsein this respect analogous to FIG. 6Aa plurality of regions that are separate from one another, with in turn the angle distributions generated by the aforementioned regions for the DOEs 722, 733 corresponding or else being able to be different from one another.
[0064] Even though, as described above, the generation according to the design of FIG. 7 of two partial beams which are linearly polarized in each case is advantageous, the optical path (formed by components 712, 731, 732 and 733) used to generate the second partial beam may also be dispensed with in further embodiments. In particular, the light may be unpolarized in this case.
[0065] The steering of electromagnetic radiation according to the disclosure to a sensor arrangement via at least one beam shaping unit may, as illustrated on the basis of FIG. 8A-8D, also be used to adjust and control the installed position of the optical system forming the heating arrangement or of the components thereof, it being possible for example to diagnose an (e.g., thermally induced) drift. In FIG. 8A-8D, 801, 802 and 803 denote light spots generated by the deflection at the location of the sensor arrangement, while 811, 812 and 813 denote intensity sensors of the sensor arrangement. The intensity sensors 811-813 facilitate a spatially resolved intensity measurement, and so the scenarios schematically indicated in FIG. 8B (corresponding to decentration), FIG. 8C (corresponding to a tilt) and FIG. 8D (corresponding to a twist) are able to be diagnosed. In this case, the sensor arrangement formed by the intensity sensors 811-813 is placed in the direct vicinity of the optical element to be heated or the EUV mirror, in particular also in a region situated outside of the optical element's used region on the optical element itself.
[0066] Even though the disclosure has 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 through 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.
