Heating arrangement and method for heating an optical element

Abstract

This invention relates to a heating configuration and a method for heating optical elements, particularly a photolithography exposure apparatus. A heating configuration according to the invention includes at least one beamforming unit (12, 22, 32, 42, 52, 54) for beamforming electromagnetic radiation directed from a radiation source to at least one optical element (25, 35, 45, 55a, 55b); and a sensor configuration having at least one intensity sensor (13, 23, 33a, 33b, 43, 53), wherein the at least one beamforming unit includes at least one microstructure element that, when the heating configuration is in operation, directs some electromagnetic radiation to the sensor configuration.

Description

Technical Field

[0001] [Interactive Reference]

[0002] This patent application claims priority to German patent application No. DE 10 2021 206 203.2, filed on June 17, 2021, the contents of which are incorporated herein by reference.

[0003] This invention relates to a heating configuration and a method for heating optical elements, particularly a photolithography exposure apparatus. Prior Technology

[0004] Lithography is used to produce microstructured components, such as integrated circuits or LCDs. This lithography process is performed within a known projection exposure apparatus, which includes an illumination device and a projection lens. An image of a photomask (=reduced photomask) illuminated by the illumination device is projected, in this case, onto a substrate (e.g., a silicon wafer) coated with a photosensitive layer (photoresist) disposed within the image plane of the projection lens, to transfer the photomask structure to the photosensitive coating on the substrate.

[0005] In projection lenses designed for the EUV range (i.e., at wavelengths of, for example, about 13 nm or approximately 7 nm), mirrors are used as optical components for the imaging process due to the lack of suitable available light-transmitting and refractive materials.

[0006] One problem encountered in practice is that EUV mirrors can heat up and undergo thermal expansion or deformation due to absorption of radiation emitted by the EUV source and other factors, which can then negatively impact the imaging characteristics of the optical system. Several methods are known to be available to avoid surface deformation caused by heat input into the EUV mirror.

[0007] One exemplary method involves using a heating configuration based on electromagnetic radiation. With this configuration, active mirror heating can occur during a relatively low absorption phase of the EUV radiation used, where the active mirror heating decreases relatively as the absorption of the EUV radiation increases. Furthermore, the EUV mirror can be preheated to a so-called zero-crossing temperature before actual operation or before EUV radiation irradiates it, at which the coefficient of thermal expansion has zero-degree thermal dependence in its temperature dependence, and in its vicinity there is no thermal expansion of the mirror substrate material, or only negligible thermal expansion.

[0008] Generating the required heating profile (which should take into account varying radiation intensities, such as the intensity of illumination used on the optically effective surface of the EUV mirror, or even variations at local levels) is a significant challenge, including in this case, providing the electromagnetic radiation required for heating.

[0009] The electromagnetic radiation required for heating is typically guided from the relative laser source to the actual optical unit containing the various optical components in the heating configuration via optical glass fibers. In addition to installation space limitations that must be considered, practical problems arising in this case include the heating configuration's susceptibility to failures, such as fiber breakage, but also due to failures of optical components present within the heating configuration (e.g., failures due to contamination and / or absorption).

[0010] Against this backdrop, it is practically necessary to ensure that the electromagnetic radiation generated by the heated optical elements (e.g., EUV mirrors) also exits the optical system forming the heated configuration throughout the entire heating configuration operation. Another practical challenge involves precisely adjusting the optical system forming the heated configuration (e.g., regarding possible eccentricity and / or tilt in relative mounting positions).

[0011] Regarding prior art, patent case DE 102017 207 862 A1 is cited as an example for reference. Summary of the Invention

[0012] One object of the present invention is to provide a heating configuration and a method for heating optical elements in an optical system, particularly in a photolithography exposure apparatus. This heating configuration and method are advantageous in effectively avoiding surface deformation and resulting optical aberrations caused by heat input to the optical elements, while at least partially avoiding the aforementioned problems.

[0013] This objective is achieved by the heating configuration and method according to the features of the alternative independent application.

[0014] A heating configuration for heating an optical element using electromagnetic radiation includes: - At least one beamforming unit for beamforming electromagnetic radiation guided from a radiation source to at least one optical element; and - A sensor configuration having at least one intensity sensor, - The at least one beamforming unit includes at least one microstructure element that directs some electromagnetic radiation to the sensor configuration when the heating configuration is in operation. In particular, the radiation source can be a laser light source, but in other specific embodiments it can also be a source emitting different radiation or an object emitting radiation. Electromagnetic radiation directed from the radiation source to the optical element for heating the optical element can impact the optically effective surface or the back of the optical element. Furthermore, the electromagnetic radiation can be infrared radiation or radiation of different wavelengths.

[0015] In particular, the present invention is based on the concept of using a beamforming unit (and particularly in a specific embodiment having at least one diffractive or refractive optical element) that is typically present in a heating configuration to direct some electromagnetic radiation to a sensor configuration containing at least one intensity sensor when the function of the heating configuration is being monitored. This heating configuration is used to heat the optical element using electromagnetic radiation, particularly in lithography exposure apparatuses.

[0016] In other words, the present invention specifically provides the use of one or more diffraction (or refraction) elements, etc., to transmit electromagnetic radiation to one or more predetermined locations in angular space, wherein one or more intensity sensors process the relevant electromagnetic radiation and determine the required information in each case. Therefore, the proper functioning of the heating configuration can be monitored or ensured at all times during its operation. Furthermore, as will be described in more detail below, the information obtained by the sensor configuration according to the present invention can also be used to drive or control the radiation source (in particular its source power) that generates electromagnetic radiation. Moreover, this information can also be used to measure or adjust the position of the optical system forming the heating configuration relative to the element to be heated, as will be described in more detail below.

[0017] According to the invention, using a beam-forming unit present within the heating configuration and, in particular, in the form of at least one diffractive optical element, outputting coupled radiation in the direction of the sensor configuration has several advantages in this case:

[0018] First, as described below, multiple regions (distinct from one another) of the associated beamforming unit or diffractive optics can direct radiation for measurement or monitoring purposes to a single intensity sensor. This is advantageous in terms of cost, considering the required installation space and the number of sensors and cable feeds, and also advantageous considering the undesirable dynamic effects that may occur during operation. In this case, the location of the sensor configuration can be freely chosen in any way, either within or outside the optical system forming the heating configuration, depending on the specific installation space conditions.

[0019] Since the beam shaping unit or at least one diffractive optical element used for radiation output coupling according to the present invention is a component that is typically present within the heating configuration in any case, the output coupling of the (measuring) beam guided to the sensor configuration according to the present invention does not require additional optical elements. Furthermore, if the beam shaping unit or diffractive optical element is designed with a plurality of separate regions, these regions can be designed independently of each other in terms of the relative emitted electromagnetic radiation intensity and (measuring) beam shape relative to the light used.

[0020] According to the present invention, the increased expenditure (regarding the generation of one or more additional measurement beams, thus increasing the complexity of the DOE design) in specific embodiments relating to the beam shaping unit and at least one diffraction optical element is acceptable in order to obtain the aforementioned advantages, particularly reliable functional monitoring.

[0021] According to one specific embodiment, the microstructured element is a diffractive optical element (DOE) or a refractive optical element (ROE).

[0022] According to one embodiment, at least one beamforming unit has a plurality of separate regions that deflect incident electromagnetic radiation in different directions from each other.

[0023] According to one specific embodiment, the sensor configuration includes a plurality of intensity sensors.

[0024] According to one embodiment, individual regions of the beam shaping unit deflect electromagnetic radiation to intensity sensors that are different from each other.

[0025] According to one embodiment, the heating configuration includes a plurality of beam-shaping units for irradiating different optical elements, which, when the heating configuration is in operation, direct some electromagnetic radiation to a common sensor configuration.

[0026] According to one embodiment, the heating configuration includes a drive unit for driving a radiation source based on a signal from the sensor configuration.

[0027] According to one embodiment, the heating configuration includes a control unit for controlling the radiation source function based on signals from the sensor configuration.

[0028] According to one specific embodiment, the optical element is a reflector.

[0029] According to one specific embodiment, the optical element is designed for operating wavelengths less than 30 nm, particularly less than 15 nm.

[0030] The present invention relates more to a method for heating an optical element in an optical system, particularly using a heating configuration having the aforementioned features, wherein electromagnetic radiation from a radiation source strikes the optical element via at least one beam shaping unit including at least one microstructured element, some of the electromagnetic radiation being guided by the at least one microstructured element to a sensor configuration including at least one intensity sensor, and the intensity of the portion of the electromagnetic radiation being detected by the sensor configuration.

[0031] According to one specific embodiment, the power of the radiation source is controlled based on signals from the sensor configuration.

[0032] According to one specific embodiment, the heating configuration used is adjusted based on signals from the sensor configuration.

[0033] According to one specific embodiment, the optical element is heated to reduce spatial and / or temporal variations in temperature distribution within the optical element.

[0034] Regarding the advantages of this method and further preferred embodiments, refer to the above explanation in conjunction with the heating configuration according to the present invention.

[0035] Furthermore, the present invention also relates to an optical system, particularly a photolithography exposure apparatus, having at least one optical element and a heating configuration for heating the optical element, the heating configuration being specifically implemented using the aforementioned features.

[0036] Further configurations of the invention can be derived from the implementation methods and various appendices.

[0037] The invention will now be explained in more detail with reference to exemplary embodiments illustrated in the accompanying drawings. Simple Explanation of the Diagram

[0038] In the diagram:

[0039] Figures 1 to 5 show schematic diagrams illustrating basic possible specific embodiments of the heating configuration according to the present invention;

[0040] Figures 6a to 6e show schematic diagrams illustrating the specific design structure and function of the heating configuration in specific embodiments of the present invention;

[0041] Figure 7 shows a schematic diagram illustrating the specific design structure and function of the heating configuration for explaining further specific embodiments of the present invention;

[0042] Figures 8a to 8d show schematic diagrams illustrating further designs and applications of the heating configuration according to the present invention; and

[0043] Figure 9 shows a possible structural schematic diagram of a lithography projection exposure device designed for EUV operation. Implementation

[0044] Figure 9 first shows a schematic diagram of a projection exposure apparatus 900 designed for operation within the EUV and in which the present invention can be implemented in an exemplary manner.

[0045] According to Figure 9, the illumination device of the projection exposure apparatus 900 includes a field plane mirror 903 and a pupil plane mirror 904. Light from a light source unit containing an EUV light source (plasma source) 901 and a focusing mirror 202 is guided onto the field plane mirror 903. A first telescope mirror 905 and a second telescope mirror 906 are disposed downstream of the optical path of the pupil plane mirror 904. A deflecting mirror 907 is disposed downstream of this optical path, and the deflecting mirror guides the radiation striking it onto an object field within the object plane of the projection lens, which includes six mirrors 921-226. At the location of the object field, a reflective structure carrying a photomask 931 is disposed on a photomask stage 930, and the photomask is imaged onto the image plane by means of the projection lens, wherein a substrate 941 coated with a photosensitive layer (photoresist) is located on the wafer stage 940.

[0046] During operation of an optical system or lithography exposure apparatus, electromagnetic radiation incident on the optically effective surface of a mirror is partially absorbed, and as explained in the prior art, this results in heating and associated thermal expansion or deformation, which in turn can impair the imaging characteristics of the optical system. The heating configuration or method for heating optical elements according to the invention can be applied, for example, to any desired mirror in the lithography exposure apparatus of FIG9.

[0047] Furthermore, the basic possible design of the heating configuration according to the present invention will first be explained with reference to Figures 1 to 5, and then the specific design of the exemplary embodiment of the present invention will be described based on Figures 6a to 6e and Figure 7.

[0048] The common feature of these basic designs or specific embodiments of the heating configuration is the use of a beamforming unit, in particular in the form of at least one diffractive optical element, and the use of the beamforming unit, especially for guiding some electromagnetic radiation to one or more predefined locations in angular space, and then acquiring the monitoring function and information required for selective use in further tasks (e.g., driving or controlling the radiation source and / or position monitoring or adjustment) through a sensor configuration including at least one intensity sensor.

[0049] Figure 1 schematically and in a very simplified representation shows a beam-forming unit 12 located within an optical system 11 and having a diffraction optical element (DOE). A portion of this beam-forming unit directs electromagnetic radiation from the optical system 11, which enters to form a heated configuration and is incident on the DOE, to a sensor configuration in the form of an intensity sensor 13. The remaining (heated) radiation not directed to the intensity sensor 13 exits from the heated configuration 11 and is used to strike optical elements (e.g., not depicted in Figure 1 but indicated in Figure 2), for example, in the form of an EUV mirror. According to the schematic example of Figure 1, the intensity sensor 13 forming the sensor configuration is located within the optical system 11.

[0050] Figure 2 also shows further basic possible designs in a schematic and more simplified manner, with components similar to or having the same basic function as those in Figure 1 indicated by reference numerals marked with "10". Compared to Figure 1, the intensity sensor 23, which forms the sensor configuration according to Figure 2, is located outside the optical system 2. The optical element to be heated is indicated by "25".

[0051] Figure 3 again shows, schematically and in a very simplified manner, a further possible basic design. Compared to Figure 2, the DOE forms a beamforming unit 32 with two separate regions 32a, 32b, which partially guides electromagnetic (heating) radiation to intensity sensors 33a, 33b, which form a sensor configuration and are different from each other.

[0052] Figure 4 shows a presentation similar to Figure 3, where components similar to or substantially the same in function as those in Figure 3 are indicated by reference numerals with added "10". Compared to Figure 3, the individual regions 42a, 42b of the DOE forming the beam shaping unit 42 guide electromagnetic radiation to an intensity sensor 43 according to Figure 4.

[0053] Figure 5 shows a schematic and very simplified representation for explaining further possible designs. According to Figure 5, the heating configuration has two separate optical systems 51a, 51b for striking separate optical elements 55a, 55b, each of which has a relative design similar to that of Figure 4. In this case, radiation guided in the sensor configuration direction by the separate regions 52a, 52b and 54a, 54b of the DOEs forming the relative beam shaping units 52 or 54 is incident on a sensor 53 of the same intensity.

[0054] Figures 6a to 6e show schematic diagrams illustrating the structure and function of a specific design for the heating configuration in a particular embodiment of the present invention.

[0055] According to FIG. 6a, the heating configuration according to the invention specifically includes a plurality of emitters 601, 602, 603, 604, which may also be presented in greater or lesser numbers. For example, emitters 601, 602, 603, 604 may be designed as IR lasers or IR LEDs (the invention is not limited thereto). According to FIG. 6a, electromagnetic radiation generated by emitters 601-604 impacts a beam shaping unit indicated by "630" via a microlens array 620, which is selectively provided to generate a collimated beam path, and from the beam shaping unit, the electromagnetic radiation impacts the optically effective surface of an optical element or mirror (not depicted in FIG. 6a).

[0056] The beam shaping unit 630 includes at least one microstructured element, particularly a diffractive optical element (DOE) or a refractive optical element (ROE). In a specific embodiment, the beam shaping unit 630 may also have a plurality of beam shaping segments, each of which can be assigned to a relative emitter 601-604. These beam shaping segments cause beam shaping and beam deflection, and electromagnetic (heating) radiation is directed to the optically effective surface of the optical element to be heated.

[0057] As shown in Figures 6a and 6b, the DOE forming the beamforming unit 630 has separate spatially separated regions 631, 632, 633, and 634. According to Figure 6c, each of these separate regions generates a first defined angular distribution 641, 642, 643, or 644 of electromagnetic radiation in angular space; for individual regions, this angular distribution can be different from each other. Furthermore, according to Figure 6d, each of these separate regions generates a second defined angular distribution 651, 652, 653, or 654 of electromagnetic radiation in angular space; for individual regions, these second angular distributions can be different from each other. These first and second angular distributions can illuminate corresponding or separate regions in real space, which can substantially have any desired form according to Figure 6e (where regions 661, 671, 664, and 674 are delineated in an exemplary manner) and can also overlap each other.

[0058] Figure 7 shows a schematic diagram illustrating the specific design structure and function of the heating configuration in another specific embodiment of the present invention.

[0059] According to Figure 7, the light beam generated by a radiation source (not depicted), which can be purely illustrative of a fiber laser used to generate IR radiation at a wavelength of, for example, 1070 nm, appears at the fiber end indicated by "701" and first passes through an optical collimator 705, which is purely illustratively composed of lenses 706 and 707. The collimated light beam exiting from the collimator 705 enters an optical assembly 710. In a specific embodiment, the fiber end 701 is, in this case, adjustable laterally (i.e., within the xy plane associated with the coordinate system plotted in the region of the fiber end 701) and axially (i.e., in the z direction associated with this coordinate system).

[0060] The optical assembly 710 (which includes a beam splitter 711 and a deflector 712 according to FIG. 7) functions to provide two beams from the initially unpolarized laser beam entering the assembly 710, each beam being linearly polarized. These linearly polarized beams can be coupled—optimally with respect to absorption—to the optical element being heated in each case (e.g., from the EUV mirror of the lithography projection exposure apparatus in FIG. 9). The advantage of generating two beams, each linearly polarized, through the optical assembly 710 is that sufficient absorption of the thermal radiation can be achieved even when the coupled thermal radiation is input at a relatively large incident angle relative to the normal of the opposing surface (so-called "grazing incidence"). This coupling of thermal radiation with "grazing incidence" input may, in turn, prove advantageous, or even necessary, in specific application cases in terms of structural space, if (typically) there is insufficient structural space in the projection exposure apparatus in the direction perpendicular to the surface of the optical element to be heated. Furthermore, depending on the specific application, this input coupling of heating radiation and grazing incidence allows for selectively ensuring that the heating configuration is positioned outside the actual beam path. Additionally, the grazing incidence input coupling allows the thermal radiation to exit the associated EUV mirror at a relatively large angle, rather than being directly redirected to an adjacent mirror. Furthermore, under appropriate polarization conditions, reflected IR radiation occurring at the EUV mirror can be reduced.

[0061] According to Figure 7, each linearly polarized partial beam exits from optical component 710 along two independent parallel beam paths along the original light propagation direction, and each passes sequentially through optical retarder 721 and 731, through diffractive optical elements (DOEs) 722 and 732, and through optical telescopes 723 and 733, respectively. Appropriate settings of the respective polarization directions can be achieved through optical retarder 721 and 731 (e.g., which may be designed as λ / 2 plates). DOEs 722 and 732 are particularly used as beam shaping units to project individual heating distributions into the optical element to be heated by beam shaping of IR radiation to be directed onto the optically effective surface of the optical element. In this case, at least one of the two DOEs 722 and 732 may be configured in a specific embodiment to be rotatable about a relative element axis for adjustment purposes, as shown in the exemplary configuration for element 732. According to Figure 7, optical telescopes 723 and 733 are composed of lenses 724-726 and 734-736, respectively, purely for illustrative purposes. In a specific embodiment, the relative final lens 726 or 736 within the beam path of one or the other of telescopes 722 and 733 can be adjusted by lateral displacement (i.e., in the xy plane relative to a coordinate system drawn in the region of lenses 726 and 736). Optical telescopes 723 and 733 are used to provide suitable additional beam deflection before electromagnetic (heating) radiation input is coupled to the optical element to be heated or enters the EUV mirror.

[0062] In the specific embodiment according to FIG. 7, DOEs 722 and 732 guide the incident electromagnetic (heating) radiation (but in this case, in conjunction with telescopes 723 and 733 downstream of the beam path) to a defined position in angular space in a manner similar to the aforementioned specific embodiment, wherein the relative distribution of radiation in angular space generated by telescopes 723 and 733 and in real space are corresponding or can be different from each other. Furthermore, each DOE 722 and 732 may have a single region (as shown in FIG. 7), or, in this pattern similar to FIG. 6A, multiple regions separated from each other, and the angular distributions generated by the aforementioned regions of DOEs 722 and 733 may correspond or be different from each other.

[0063] Even though, as mentioned above, the two-part beam of linear polarization generated according to the design of Figure 7 is advantageous in every case, in a further specific embodiment, the optical path (formed by components 712, 731, 732 and 733) for generating the second part of the beam can be omitted. In particular, in this case, the light can be unpolarized.

[0064] According to the present invention, electromagnetic radiation is guided to a sensor configuration via at least one beamforming unit, as shown in Figures 8a to 8d. This can also be used to adjust and control the mounting position of an optical system or its components forming a heating configuration, for example, to diagnose (e.g., thermally induced) drift. In Figures 8a to 8d, "801", "802", and "803" represent light spots generated by deflection at the sensor configuration location, while "811", "812", and "813" represent intensity sensors of the sensor configuration. Intensity sensors 811-813 facilitate spatially resolvable intensity measurements, thus enabling the diagnosis of the scenarios schematically indicated in Figures 8b (corresponding to eccentricity), 8c (corresponding to tilt), and 8d (corresponding to torsion). In this case, the sensor configuration formed by intensity sensors 811-813 is placed directly near the optical element to be heated or an EUV reflector, particularly in an area outside the area used by the optical element itself.

[0065] Even though the invention has been described with reference to specific embodiments, those skilled in the art will understand numerous variations and alternative embodiments, such as by combining and / or exchanging multiple features of individual embodiments. Therefore, it is self-evident that the invention covers such variations and alternative embodiments for those skilled in the art, and the scope of the invention is limited only to the claims and appendices of the following claims.

[0066] 11, 21, 51a, 51b: Optical systems 12, 32, 42, 52, 54, 630: Beamforming units 13, 23, 33a, 33b, 43, 53: Intensity sensors 25, 55a, 55b: Optical elements 32a, 32b, 42a, 42b, 52a, 52b, 54a, 54b, 631, 632, 633, 634: Individual areas 601-604: Transmitter 620: Microlens Array 641-644: First Definition of Angular Distribution 651-654: Second Definition of Angular Distribution 661, 671, 664, 674: Areas 701: Fiber Optic End 705: Optical Collimator 706, 707, 724-724, 734-736: Lenses 710: Optical Components 711: Beam Splitter 712: Deflecting Mirror 721, 731: Optical retarders 722, 732: Diffraction optical elements 723, 733: Optical telescopes 801-803: Light Spot 811-813: Intensity Sensor 900: Projection Exposure Device 901: EUV light source 902: Concentrator 903: Field Mirror 904: Pupil Split-Face Mirror 905: First telescope reflecting mirror 906: Second telescope reflecting mirror 907: Deflecting Mirror 921-926: Reflector 930: Light Mask Platform 931: Reflective structure supporting photomask 940: Wafer Stage 941: Substrate

Claims

1. A heating configuration for heating an optical element by impinging electromagnetic radiation thereon, comprising: at least one beamforming unit (12, 22, 32, 42, 52, 54) for beamforming electromagnetic radiation directed from a radiation source to the at least one optical element (25, 35, 45, 55a, 55b); and a sensor configuration having at least one intensity sensor (13, 23, 33a, 33b, 43, 53); wherein the at least one beamforming unit (12, 22, 32, 42, 52, 54) includes at least one microstructure element that, when the heating configuration is in operation, directs some electromagnetic radiation to the sensor configuration; wherein the at least one microstructure element is configured to deflect a first portion of the electromagnetic radiation from the at least one microstructure element to the at least one intensity sensor; and wherein the at least one microstructure element is configured to deflect a second portion of the electromagnetic radiation from the at least one microstructure element to the at least one optical element. The first and second portions of the electromagnetic radiation are deflected from the same location on the at least one microstructure element; the first portion of the electromagnetic radiation is different from the second portion; and the at least one optical element maintains a certain distance from the at least one intensity sensor.

2. The heating configuration as described in claim 1, characterized in that the microstructured element is a diffractive optical element (DOE) or a refractive optical element (ROE).

3. The heating configuration as described in claim 1 or 2, characterized in that the at least one beam shaping unit (32, 42, 52, 54) has a plurality of individual regions (32a, 32b, 42a, 42b, 52a, 52b, 54a, 54b) that deflect the incident electromagnetic radiation in different directions from each other.

4. The heating configuration as described in claim 1, characterized in that the sensor configuration includes a plurality of intensity sensors (33a, 33b).

5. The heating configuration as claimed in claim 3, characterized in that the individual regions (32a, 32b) of the beam shaping unit (32) deflect electromagnetic radiation to a plurality of intensity sensors (33a, 33b) differently from each other.

6. The heating configuration as claimed in claim 1, characterized in that the heating configuration includes a plurality of beam shaping units (52, 54) for striking different optical elements (55a, 55b), and when the heating configuration is in operation, these beam shaping units (52, 54) direct some electromagnetic radiation to an identical sensor configuration (53).

7. The heating configuration as claimed in claim 1, characterized in that the heating configuration includes a driving unit for driving the radiation source according to a signal from the sensor configuration.

8. The heating configuration as claimed in claim 1, characterized in that the heating configuration includes a control unit for controlling the power of the radiation source based on a signal from the sensor configuration.

9. The heating configuration as claimed in claim 1, characterized in that the optical element (25, 35, 45, 55a, 55b) is a mirror.

10. The heating configuration as claimed in claim 1, characterized in that the optical element is designed for operating wavelengths less than 30 nm, particularly less than 15 nm.

11. A method for heating an optical element in an optical system, wherein electromagnetic radiation from a radiation source strikes an optical element (25, 35, 45, 55a, 55b) via at least one beamforming unit (12, 22, 32, 42, 52, 54) comprising at least one microstructured element, wherein some of the electromagnetic radiation is guided by the at least one microstructured element to a sensor configuration comprising at least one intensity sensor (13, 23, 33a, 33b, 43, 53), and the intensity of this portion of the electromagnetic radiation is detected by the sensor configuration. Measurement; wherein the at least one microstructure element is configured to deflect a first portion of the electromagnetic radiation from the at least one microstructure element to the at least one intensity sensor; wherein the at least one microstructure element is configured to deflect a second portion of the electromagnetic radiation from the at least one microstructure element to the at least one optical element; wherein the first portion and the second portion of the electromagnetic radiation are deflected from the same location on the at least one microstructure element; wherein the first portion and the second portion of the electromagnetic radiation are different; and wherein the at least one optical element maintains a certain distance from the at least one intensity sensor.

12. The method as described in claim 11, characterized in that the power of the radiation source is controlled according to a signal from the sensor configuration.

13. The method as described in claim 11 or 12, characterized in that the heating configuration used is adjusted according to a signal from the sensor configuration.

14. The method as claimed in claim 11, characterized in that the optical element is heated such that the spatial and / or temporal variation of the temperature distribution in the optical element (25, 35, 45, 55a, 55b) is reduced.

15. An optical system, particularly in a photolithography exposure apparatus, having at least one optical element (25, 35, 45, 55a, 55b) and a heating configuration for heating the optical element (25, 35, 45, 55a, 55b), the heating configuration being implemented as described in any one of claims 1 to 10.

Images