Heating head, heating device, and optical system, in particular EUV lithography system

Abstract

The invention relates to a heating head (26) for heating an optical element, comprising: a housing (30) and at least one heating unit (29), which is accommodated in the housing (30), for supplying a surface of the optical element with thermal radiation (28). The heating unit (29) has a thermal screen (43) for absorbing scattered radiation (44). The thermal screen (43) comprises at least one screen opening for the passage of thermal radiation (28). The invention also relates to a heating device comprising: at least one heating head (26) which is designed as described above, and at least one thermal radiation source for generating thermal radiation (28) for the at least one heating unit (29) of the heating head (26). The invention also relates to an optical system which includes an optical element and a heating head (26) for heating the optical element.

Description

[0001] Heating head, heating device and optical system, in particular EUV lithography system

[0002] Reference to related application

[0003] This application claims priority from German patent application DE102023211225.6 filed on November 13, 2023, the entire disclosure of which is incorporated by reference into this application.

[0004] Background of the invention

[0005] The invention relates to a heating head for heating an optical element, comprising: a housing and at least one heating unit accommodated in the housing for applying heat radiation to a surface of the optical element. The invention also relates to a heating device having at least one such heating head and to an optical system, in particular an EUV lithography system, having such a heating device.

[0006] In optical systems in the form of lithography systems designed for the EUV wavelength range, especially in EUV

[0007] Lithography systems typically use EUV mirrors as optical elements. The EUV mirrors can heat up and experience associated thermal expansion or deformation, among other things due to the absorption of radiation emitted by an EUV light source. This can impair the imaging properties of the optical system, for example of the EUV lithography system. To avoid or at least reduce surface deformations caused by heat input into an EUV mirror, heating devices based on thermal radiation, for example in the form of infrared radiation, can be used. With the help of such a heating device, the EUV mirror can be actively heated during periods in which there is comparatively little absorption of EUV radiation, with the active heating being reduced accordingly as the absorption of EUV radiation by the EUV mirror increases.The EUV mirrors can also be preheated before the actual operation of the EUV lithography system, i.e. before the EUV mirrors are exposed to EUV radiation.

[0008] Heating devices or heating heads with heating devices for heating optical elements by applying heat radiation are known from various documents, for example from

[0009] DE102020213416A1, DE102020207748A1, DE102020207752A1 or DE102019219289A1.

[0010] Heating heads used to heat EUV mirrors are arranged in a high vacuum, so that heat from a particular heating head or from the mechanical components of a particular heating head may not be sufficiently dissipated via convection. This can lead to mechanical components such as springs, closures, etc.

[0011] Bayonets, screw rings, or sockets of heating heads heat up uncontrollably, and their thermal behavior can no longer be controlled. If a specified maximum temperature in the heating head is not maintained, this can lead to uncontrolled expansion of the material of the mechanical components and, in extreme cases, to a change in their material properties, e.g., if the temperature of the components rises to several hundred degrees Celsius. The uncontrolled expansion of socket components can lead to misalignment and, in the worst case, damage to the optical elements of the heating head. Object of the invention

[0012] The object of the invention is to provide a thermally stabilized heating head as well as a heating device and an optical system with such a heating head.

[0013] Subject of the invention

[0014] This object is achieved by a heating head of the type mentioned at the outset, in which the heating unit has at least one heat shield for absorbing scattered radiation, wherein the heat shield comprises at least one aperture for the passage of the heating radiation.

[0015] The inventors have recognized that the uncontrolled heating of mechanical components is essentially due to scattered radiation, which can arise, for example, after passing through a structured optical element in a respective heating unit. Due to this scattered radiation, mechanical components such as mounting components, e.g. in the form of springs, closures, e.g. bayonets, screw rings, etc., can expand and, as described above, possibly change their material properties under extreme load. In particular, the uncontrolled expansion of mounting components, which is due to heating by scattered radiation, can lead to the misalignment described above or possibly to damage to the mounted optical elements.

[0016] The heat shield absorbs scattered radiation and dissipates the heat absorbed during absorption in a defined manner. The heat that would otherwise be absorbed at critical points within the heating head, such as socket components, can be directed to non-critical points within the heating head with the help of the heat shield, thus contributing to the thermal stabilization of the heating head. The heat shield specifically shades the mechanical components of the heating head that are relevant to uncontrolled thermal expansion. The heat shield can therefore prevent uncontrolled heating of mechanical components of the heating head.

[0017] In one embodiment, the heating unit has at least one optical element that generates the scattered radiation in front of the heat shield in the beam path of the heating radiation. The scattered radiation is typically generated when the heating radiation passes through a transmitting optical element, more precisely when it passes through surfaces of the transmitting optical element that are not completely smooth. It is also possible for the scattered radiation to be generated when the heating radiation is reflected by a reflective optical element of the heating unit, for example, by a mirror that has a surface that is not completely smooth.

[0018] In a further development, the optical element causing the scattered radiation is designed as a structured optical element, in particular as a Fresnel lens or as a Fresnel lens arrangement. The structured optical element can be a component of a collimator, which serves to collimate the heating radiation when it emerges from a fiber connector, which serves to connect the heating unit to one or more optical fibers (see below). The structured optical element can, for example, be a Fresnel lens, which has one or possibly two structured surfaces. However, it can also be a Fresnel lens arrangement, which has a plurality of Fresnel lenses. The Fresnel lenses of the lens arrangement can be designed in the form of a plurality of individual lenses, which form a Fresnel lens array. However, the Fresnel lens arrangement can also be a single optical element, which, for example,has several structured segments, each designed in the form of a Fresnel lens. The structured optical element does not necessarily have to be a Fresnel lens or a Fresnel lens arrangement; it can also be another type of structured optical element, for example, a diffractive optical element.

[0019] In a further embodiment, an edge of the diaphragm opening is arranged outside a beam path of the heating radiation. The heat diaphragm typically does not serve as an aperture diaphragm to limit the edge of the beam path of the heating radiation, but merely to absorb scattered radiation that propagates outside the beam path of the heating radiation. To prevent the edge of the heat diaphragm from representing a light-limiting edge during thermal expansion, the edge of the heat diaphragm has a safety distance from the outer circumference of the beam path. The distance is dimensioned such that the heat diaphragm does not expand so far that the edge of the diaphragm opening reaches the outer circumference of the beam path of the heating radiation, even at the maximum heat load impinging on it and thus at its maximum operating temperature.The safety distance can be determined, for example, in the manner described in DE102020208007A1, which is incorporated by reference in its entirety into the content of this application.

[0020] In a further embodiment, the heat shield is designed to at least partially shade at least one socket component of the heating unit. To shield the socket component(s) as efficiently as possible from scattered radiation, it is advantageous if the heat shield is positioned near the socket component(s) to be shielded. It is understood that the heat shield can also be designed to at least partially shade mechanical elements of the heating unit other than socket components.

[0021] In a further embodiment, the heat shield and / or the housing is / are made of a metallic material, in particular stainless steel or copper. Metallic materials generally have a high thermal conductivity, on the order of approximately 10 W / (m K) or higher. The use of a material with good thermal conductivity for the heat shield and for the housing is advantageous for efficient heat dissipation. To dissipate heat from the heating head, the heating head, or more precisely the housing of the heating head, can be connected to a heat sink. The heat sink can be, for example, a support frame or the like to which the heating head is attached.

[0022] In a further development, the heat shield has at least one ventilation opening located outside the beam path of the heating radiation. In this case, the heating head is typically arranged in an environment that is evacuated before operation of the optical system. The ventilation opening serves to generate an air flow during evacuation, which is guided past the optical elements of the heating unit to prevent the accumulation of particles on the optical elements of the heating unit as much as possible.

[0023] In another embodiment, the heat shield is attached to the housing via a heat-conducting connection. For efficient dissipation of the heat absorbed by the heat shield, a good heat-conducting connection between the heat shield and the housing and / or other mechanical components of the heating head is advantageous. A heat-conducting connection can be created in various ways.

[0024] In a further development of this embodiment, the heat-conducting connection is established by screwing or by bonding. If the heat-conducting connection is realized by screwing, it is advantageous if the respective screw connections are implemented with a high surface pressure. To improve heat conduction, the number of screw connections used to attach the heat shield to the housing can be increased. A good heat-conducting connection between the shield and the housing and / or other mechanical components can also be achieved by bonding. The housing can be constructed in one or more parts.

[0025] In one embodiment, the housing comprises a first housing part and a second housing part, and the heat shield is mounted between the two housing parts. The heat shield can be clamped between the two housing parts, in particular if the two housing parts are connected to each other via a screw connection. Sockets for the optical elements of the heating unit can be accommodated in the first housing part and / or the second housing part.

[0026] In a further embodiment, the heating unit has a polarization beam splitter for splitting the heating radiation into two differently polarized heating radiation components. With the aid of a heating unit that has a polarization beam splitter for splitting the heating radiation into two differently polarized heating radiation components, the two heating radiation components can be polarized in parallel with respect to the plane of incidence of the heating radiation onto the surface of the optical element (p-polarization)—usually with the additional use of (at least) one polarization modulator. With a suitable choice of the angle of incidence, typically close to the Brewster angle, the reflectivity of the surface for the heating radiation can be significantly reduced, as described, for example, in DE102020213416 A1 cited above.

[0027] In a further development of this embodiment, the heat shield is arranged in the beam path of the heating radiation downstream of the polarization beam splitter and has two apertures for the passage of one of the two heating radiation components. It has been shown that it is advantageous for the thermal stabilization of the heating head if the heat shield - usually formed as a single piece - is arranged in the beam path downstream of the polarization beam splitter and has two apertures for each of the two heating radiation components. Instead of a common heat shield for the two heating radiation components, two heat shields can in principle also be used, each having an aperture for the passage of a respective heating radiation component.

[0028] In a further embodiment, the heating head has at least one fiber connector for connecting the heating unit to at least one optical fiber. Typically, the heating radiation is supplied to the heating head via one or more optical fibers. A separate fiber connector can be provided for each optical fiber, but it is also possible for several, in particular all, optical fibers of the heating unit to be connected to the heating head via a common fiber connector. An optical fiber typically serves to supply the heating radiation from a heating radiation source that is assigned to the respective optical fiber. The heating radiation typically exits an exit-side end of the or a respective optical fiber and is guided in free-jet propagation in the heating unit.The optical fiber is an optical fiber designed to guide the heating radiation from the heating radiation source to the fiber connector of the heating head. Instead of optical fibers, other types of optical waveguides can also be used to deliver the heating radiation to the heating head.

[0029] A further aspect of the invention relates to a heating device, comprising: at least one heating head, which is designed as described above, and at least one heat radiation source, which is designed to generate heat radiation for the at least one heating unit of the heating head. The heat radiation source is typically an IR radiator, for example an IR laser or an IR LED. To generate a desired heat radiation profile on the surface of the optical element, the heat radiation source(s) assigned to a respective heating unit can be specifically activated or deactivated. The heating device can, in particular, have a plurality of heating heads.As described in DE 102020207748 A1 cited above, the use of two or more separate heating heads can, for example, achieve a "crossed" coupling of the heating radiation generated by the heating heads into the optical element. However, such coupling of the heating radiation is not mandatory.

[0030] A further aspect of the invention relates to an optical system, in particular an EUV lithography system, comprising: at least one optical element, in particular a mirror, and a heating device for heating the optical element, which heating device is designed as described above. The EUV lithography system can be an EUV lithography system for exposing a wafer or another optical arrangement that uses EUV radiation, for example an EUV inspection system, e.g. for inspecting masks, wafers or the like used in EUV lithography. It is understood that a plurality of heating devices can be arranged in the optical system, each of which is designed to heat an optical element. The optical system does not necessarily have to be an EUV lithography system; it can be, for example, a DUV lithography system or another type of optical system.

[0031] The heating head(s) can be aligned such that the heating radiation strikes the surface of the optical element at an angle of incidence in the range of the Brewster angle. In this way, it can be achieved that the largest possible proportion of the heating radiation is absorbed by the optical element, as described with regard to the heating units in DE102020213416A1 cited above. Further features and advantages of the invention emerge from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be implemented individually or in groups in any desired combination in a variant of the invention.

[0032] drawing

[0033] Examples of embodiments are shown in the schematic drawing and are explained in the following description.

[0034] Fig. 1 shows a meridional section of a projection exposure system for EUV projection lithography,

[0035] Fig. 2 is a schematic representation of an optical element in the form of an EUV mirror and a heating device with two heating heads for applying heating radiation to a surface of the optical element,

[0036] Fig. 3 is a schematic representation of a heating head with a heating unit having a heat shield, and

[0037] Fig. 4 is a schematic representation of a top view of the heat shield of Fig. 3.

[0038] In the following description of the drawings, identical reference numerals are used for identical or functionally identical components. The essential components of an optical arrangement for EUV lithography in the form of a projection exposure system 1 for microlithography are described below with reference to Fig. 1. The description of the basic structure of the

[0039] Projection exposure system 1 and its components are not to be understood as restrictive.

[0040] An embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be a

[0041] A separate module may be provided for the lighting system. In this case, the lighting system does not include light source 3.

[0042] A reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced, in particular in a scanning direction, via a reticle displacement drive 9.

[0043] For illustrative purposes, a Cartesian xyz coordinate system is shown in Fig. 1. The x-direction runs perpendicular to the drawing plane. The y-direction runs horizontally, and the z-direction runs vertically. The scanning direction in Fig. 1 runs along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0044] The projection exposure system 1 comprises a projection system 10. The projection system 10 is used to image the object field 5 into an image field 11 in an image plane 12. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular along the y-direction, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0045] The radiation source 3 is an EUV radiation source. The radiation source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation has, in particular, a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example, an LPP source (laser produced plasma) or a DPP source (gas discharged produced plasma). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free-electron laser (FEL).

[0046] The illumination radiation 16 emanating from the radiation source 3 is focused by a collector mirror 17. The collector mirror 17 can be a collector mirror with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector mirror 17 can be exposed to the illumination radiation 16 at grazing incidence (Gl), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector mirror 17 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0047] After the collector mirror 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the radiation source 3 and the collector mirror 17, and the illumination optics 4.

[0048] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. The first facet mirror 20 comprises a plurality of individual first facets 21, which are also referred to below as field facets. Only a few of these facets 21 are shown in Fig. 1 as examples. A second facet mirror 22 is arranged downstream of the first facet mirror 20 in the beam path of the illumination optics 4. The second facet mirror 22 comprises a plurality of second facets 23.

[0049] The illumination optics 4 thus form a double-faceted system. This basic principle is also referred to as a fly's-eye integrator. With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror, or indeed the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0050] The projection system 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0051] In the example shown in Fig. 1, the projection system 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection system 10 is a doubly obscured optical system. The projection optical system 10 has an image-side numerical aperture that is greater than 0.4 or 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0052] The mirrors Mi, just like the mirrors of the illumination optics 4, can have a highly reflective coating for the illumination radiation 16.

[0053] It may be advantageous if individual or possibly all mirrors Mi of the projection optics 10 are heated. Fig. 2 shows a highly schematic view of a mirror Mi of the projection optics 10 to be heated, as well as a heating device 25 used to heat the mirror Mi. To heat the mirror Mi, the heating device 25 has a heating head 26 and another heating head 26'. In the example shown, the two heating heads 26, 26' are identical in construction and arranged on opposite sides of the mirror Mi. The mirror Mi comprises an optical surface 27, which is struck by the EUV radiation 16.

[0054] The heating head 26 emits heating radiation 28, which impinges in the form of a beam onto a first partial area of ​​the optical surface 27 of the mirror Mi, designated "A" in Fig. 2, which faces the further heating head 26'. Accordingly, the further heating head 26' emits heating radiation 28', which impinges in the form of a beam onto a second partial area of ​​the optical surface 27 of the mirror Mi, designated "B" in Fig. 2, which faces the heating head 26. The beams of heating radiation from the two heating heads 26, 26' intersect or cross each other on their way to the optical surface 27. It is understood that more than two heating heads 26, 26', ... can be used to apply heating radiation 28, 28', ... to the optical surface 27 of the mirror Mi.can be used, for example three heating heads arranged in a regular array around the mirror Mi, as is the case with the heating units described in DE102020207748A1.

[0055] The two heating heads 26, 26' of the heating device 25 described here each have a heating unit 29, 29', which is integrated into or arranged within a housing 30, 30' of the respective heating head 26, 26'. In principle, it is also possible for two or more heating units to be provided in a respective housing 30, 30'.

[0056] The heating units 29, 29' of the heating heads 26, 26' are connected to a respective heating radiation source 33a to 33g, 33a' to 33g' via a respective fiber connector 31, 31', which is attached to the housing 30, 30' of the respective heating head 26, 26', via a number of optical fibers 32a to 32g, 32a' to 32g' (in the example shown), seven. The heating radiation source 33a to 33g, 33a' to 33g', which is assigned to a respective optical fiber 32a to 32g, 32a' to 32g' of one of the heating units 29, 29', can be activated or deactivated with the aid of a control device (not shown) in order to generate different heating radiation profiles on the optical surface 27 of the mirror Mi. In the example shown, the heat radiation sources 33a to 33g, 33a' to 33g' are IR radiators, for example IR lasers or IR LEDs, which are designed to generate heat radiation in the near infrared wavelength range.

[0057] Fig. 3 shows the heating head 26 of Fig. 2 with the heating unit 29 in a sectional view. The heating radiation 28 generated by the heating radiation sources 33a to 33g and guided by the optical fibers 32a to 32g to the heating head 26 (cf. Fig. 2) exits the fiber ends of the optical fibers 32a to 32g in the housing 30. The heating radiation 28 exiting the fiber ends is guided in the heating unit 29 in free-beam propagation via common optics. The heating radiation 28 first passes through an optical collimator 34, which may have one or more lenses. In the example shown, the collimator 34 has a Fresnel lens arrangement 35 as the last optical element in the beam path; however, the Fresnel lens arrangement 35 does not necessarily have to be the last optical element of the collimator 34.In the example shown, the Fresnel lens arrangement 35 comprises a plate-shaped base body whose surface has seven sectors, each structured in the form of a Fresnel lens. The heating radiation 28 emitted by one of the optical fibers 32a to 32g impinges on each of the sectors and is collimated by the respective Fresnel lens. It is understood that the Fresnel lens arrangement 35 can also be designed in a different way, for example, in the form of a Fresnel lens array or the like.

[0058] The heating radiation 28 emerging collimated from the collimator 34 subsequently enters an optical component 36. The fiber end or the position of the heating unit 29 relative to the fiber end can be adjustable both laterally (within the xy plane of the coordinate system shown in the region of the fiber end) and axially (in the z direction of this coordinate system).

[0059] The optical component 36, which in the example shown is made of quartz glass, serves to split the heating radiation 28 into two linearly polarized heating radiation components 28a, 28b and for this purpose has a polarization beam splitter 37. The first heating radiation component 28a is transmitted by the polarization beam splitter 37 and retains the original propagation direction. The second heating radiation component 28b is deflected or reflected by 90° within the optical component 36 at the polarization beam splitter 37 and strikes a flat deflection surface 38, which, through total internal reflection, deflects or reflects almost the entire power of the second heating radiation component 28b again by 90°. As can also be seen in Fig. 3, the first heating radiation component 28a and the second heating radiation component 28b exit the optical component 36 offset in parallel. A respective heat radiation component 28a, b passes successively through an optical retarder 39a or39b, a beam-shaping device 40a or 40b in the form of a diffractive optical element, and an optical telescope 41a or 41b. The two heating radiation components 28a, 28b emerge from the heating head 26 laterally offset after passing through the respective optical telescope 41a or 41b and together form the heating radiation 28, which is applied to the surface 27 of the mirror Mi.

[0060] The two optical retarders 39a and 39b, which can be designed, for example, as λ / 2 plates, can be used to adjust the respective polarization direction of the two heating radiation components 28a, b. The two diffractive optical elements serve as beam-shaping units 40a and 40b, respectively, for imprinting an individual heating radiation profile (intensity profile) on the surface 27 of the mirror Mi to be heated by means of beam shaping. In the example shown, the heating radiation profile is a top-hat profile. The diffractive optical element 40b, through which the second heating radiation component 28b passes, can be rotatably mounted for adjustment purposes, but this is not absolutely necessary.

[0061] The optical telescopes 41a and 41b are each constructed from several lenses in Fig. 3, two of which are illustrated. The optical telescopes 41a and 41b serve to provide suitable additional beam deflection or beam expansion before the surface 27 of the mirror Mi is exposed to the heating radiation 28.

[0062] The above-described generation of two linearly polarized

[0063] Heating radiation components 28a, b make it possible to align the polarization direction of the heating radiation 28, which is unpolarized upon entering the heating unit 29, with respect to a plane of incidence (not shown) on the surface 27 of the mirror Mi in a parallel polarized (p-polarized) manner upon exiting the heating unit 29. With a suitable choice of the angle of incidence in the range of the Brewster angle, the reflection of the heating radiation 28 at the surface 27 of the mirror Mi can be minimized and the absorption of the heating radiation 28 can be maximized.

[0064] In the example shown, the housing 30 of the heating head 26 has two housing parts 30a, 30b, which are connected or fastened to one another via a screw connection 42 having a plurality of screw connections. A heat shield 43 is arranged between the two housing parts 30a, 30b and is clamped or fixed between the housing parts 30a, 30b via the screw connection. The screw connection 42 creates a surface pressure on the heat shield 43, which creates a heat-conducting connection between the heat shield 43 and the housing 30. This is advantageous for efficiently dissipating heat from the heat shield 43 and transporting it via the housing 30 to a heat sink (not shown), which can be, for example, a support structure on which the heating head 26 is held or a heat sink that is in contact with the outside of the housing 30.It is also possible to actively cool the heating head 26 by introducing cooling channels into the housing 30 through which a cooling fluid, e.g., water, flows. In the example shown, both the housing parts 30a, 30b and the heat shield 43 are made of a metallic material, namely stainless steel.

[0065] The heat shield 43, shown in dashed lines in Fig. 3, serves to absorb scattered radiation 44, shown in dash-dotted lines in Fig. 3, which is generated by the Fresnel lens arrangement 35. The heat shield 43 absorbs the scattered radiation 44 so that it cannot reach the mounting components 45a arranged in the beam path after the heat shield 43. The mounting components 45a, which are not shown in detail, can be, for example, closures, springs, screw rings, etc. In Fig. 3, the scattered radiation that would impinge on the mounting components 45a without the provision of the heat shield 43 is shown in dotted lines.

[0066] For efficient shading of the mounting components 45a that should not be affected by the scattered radiation 44, it is advantageous if the heat shield 43 is positioned as close as possible to the mounting components 45a. A portion of the scattered radiation 44 is redirected via the polarization beam splitter 37 and can therefore also reach the mounting components 45b of the optical elements 39b, 40b, 41b, which are arranged in the beam path of the second heating radiation component 28b. These mounting components 45b can also be protected from the scattered radiation 44 with the aid of the heat shield 43.

[0067] The heat shield 43 shown in a plan view in Fig. 4 has, in the example shown, two apertures 46a, 46b, which serve to allow the first heat radiation component 28a and the second heat radiation component 28b to pass through. As can also be seen in Fig. 4, an annular peripheral edge 47a, 47b of the respective aperture 46a, 46b is spaced from the beam path 48a, 48b, more precisely, from the outer edge of the beam path 48a, 48b of the respective heat radiation component 28a, 28b. This ensures that the heat shield 43 serves only to dissipate heat and does not perform an optical function. Instead of the one-piece heat shield 43 shown in Fig. 4, two heat shields can also be used if necessary to absorb the scattered radiation 44 of the first heating radiation portion 28a and the second heating radiation portion 28b.

[0068] In addition to the two apertures 46a, 46b, the heat shield 43 has further openings through which screws can pass to secure the heat shield 43 between the two housing parts 30a, 30b. The heat shield 43 also has ventilation openings 49, which redirect the air flow in a desired manner when evacuating the lithography system 1 or the heating head 26. It is understood that the arrangement and geometry of the ventilation openings 49 may differ from the illustration in Fig. 4.

[0069] It is also understood that the heating unit 29 does not necessarily have to be designed in the manner described here, but can also be designed in a different way. For example, the heating unit 29 may not have a polarization beam splitter 37 in order to split the heating radiation 28 into two heating radiation components 28a, b. In this case, the components of the heating unit 29 that are required for guiding the beam of the second heating radiation component 28b are omitted. Furthermore, the optical retarder 39a can also be omitted, since the heating radiation 28 exits the heating unit 29 unpolarized in this case. In this case, the heating radiation 28 can be radiated essentially perpendicular to the surface 27 of the mirror Mi, i.e., it is not necessary to radiate the heating radiation 28 onto the surface 27 at an angle of incidence that essentially corresponds to the Brewster angle.The heating unit 29 or several heating units 29 can also be accommodated in the housing 30 in this case. Possible other embodiments of the heating unit 29 are described, for example, in the above-cited DE102020213416A1, in DE102020207748A1, or in DE102020207752A1, each of which is incorporated in its entirety by reference into the content of this application.

Claims

Patent claims 1 . Heating head (26) for heating an optical element (Mi), comprising: a housing (30), at least one heating unit (29) accommodated in the housing (30) for applying heating radiation (28) to a surface (27) of the optical element (Mi), wherein the heating unit (29) has a heat shield (43) for absorbing scattered radiation (44), wherein the heat shield (43) comprises at least one aperture (46a, 46b) for the passage of the heating radiation (28), and wherein the heat shield (43) is designed to at least partially shade at least one mounting component (45a, 45b) of the heating unit (29).

2. Heating head according to claim 1, wherein the heating unit (29) has at least one optical element (35) generating the scattered radiation (44) in front of the heat shield (43) in the beam path of the heating radiation (28).

3. Heating head according to claim 2, wherein the optical element generating the scattered radiation (44) is designed as a structured optical element, in particular as a Fresnel lens or as a Fresnel lens arrangement (35).

4. Heating head according to one of the preceding claims, in which an edge (47a, 47b) of the aperture (46a, 46b) is arranged outside the beam path (48a, 48b) of the heating radiation (28).

5. Heating head according to one of the preceding claims, in which the heat shield (43) and / or the housing (30) is formed from a metallic material, in particular from stainless steel or copper.

6. Heating head according to one of the preceding claims, in which the heat shield (43) has at least one ventilation opening (49) which is arranged outside the beam path (48a, 48b) of the heating radiation (28).

7. Heating head according to one of the preceding claims, wherein the heat shield (43) is attached to the housing (30) via a heat-conducting connection (42).

8. Heating head according to claim 7, wherein the heat-conducting connection is made by a screw connection (42) or by an adhesive connection.

9. Heating head according to one of the preceding claims, wherein the housing (30) has a first housing part (30a) and a second housing part (30b) and the heat shield (43) is mounted between the two housing parts (30a, 30b).

10. Heating head according to one of the preceding claims, in which the heating unit (29) has a polarization beam splitter (37) for dividing the heating radiation (28) into two differently polarized heating radiation components (28a, b).

11. Heating head according to claim 10, wherein the heat diaphragm (43) is arranged in the beam path of the heating radiation (28a) after the polarization beam splitter (37) and has two diaphragm openings (46a, 46b) for the passage of one of the two heating radiation components (28a, b).

12. Heating head according to one of the preceding claims, further comprising: at least one fiber connector (31) for connecting the heating unit (29) to at least one optical fiber (32a-g).

13. Heating device (25), comprising: at least one heating head (26, 26') according to one of the preceding claims, and at least one heat radiation source (33a-g) which is designed to generate heat radiation (28) for the at least one heating unit (29) of the heating head (26, 26').

14. Optical system, in particular EUV lithography system (1), comprising: an optical element, in particular a mirror (Mi), and a heating device (25) according to claim 13 for heating the optical element (Mi).

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