Arrangement comprising a microlithographic projection system and a wall element for thermal shielding and projection exposure system

Abstract

The arrangement comprises a projection system (22) for microlithography and a wall element (28) for thermally shielding the projection system (22) from an illumination system (10). The projection system (22) has an object field that can be illuminated by the illumination system (10) and optical elements (M1-M6) for imaging the object field onto an image plane (21). The wall element (28) also includes a passive shielding surface element (30) arranged in a transition region between a last beam section (41) of the illumination system (10) and a first beam section (42) of the projection system (22). According to the invention, the arrangement further comprises an active cooling element (31) positioned in the transition region, with a cooling surface (32) that extends at least partially along a surface area of ​​the passive shielding surface element (30).The active cooling element positioned in the transition area can significantly reduce the rate of change of the heat flow from the lighting system to the projection system.

Description

[0001] The present invention relates to an arrangement comprising a microlithographic projection system and a wall element for thermal shielding the projection system from a lighting system.

[0002] Microlithographic projection exposure systems, comprising an illumination system and a projection system, are used for the fabrication of microstructured components. Achieving high image quality depends not only on the quality of the individual optical elements of the projection system but also on their relative positions. To ensure these relative positions during operation of a projection exposure system, it is known to mount the individual optical elements of the projection system on a common support frame. The support frame and the optical elements are actively temperature-controlled at regular intervals to reduce changes in the image quality of the projection system due to thermal expansion of the optical elements or the support structure. For example, the support frame and / or optical elements can be permeated with channels for a thermofluid.By passing thermofluid through these channels at a predetermined flow rate and / or temperature, the temperature of the support frame and / or optical elements can be kept relatively constant. These measures are intended to minimize deformation of the support frame and / or optical elements during operation.

[0003] Furthermore, actuators can be provided between the support frame and the individual optical elements, allowing the position of each optical element relative to the support frame to be readjusted. This compensates for minor deformations of the support frame or the optical elements caused by slight temperature changes, which cannot be completely eliminated.

[0004] Despite the possibilities for actively controlling the temperature of the optical elements and / or the support frame, as well as for readjusting the optical elements, image quality can deteriorate if the heat input into the projection system is too high. Increased heat input can originate particularly from the lighting system when using illumination radiation with very short wavelengths, as this radiation has higher energy and, moreover, a larger proportion of the energy tends to be absorbed by the optical elements of the lighting system. To reduce heat input from the lighting system, it is generally known to install a wall element for thermal shielding between the lighting system and the projection system.

[0005] The object of the present invention is to provide an arrangement comprising a projection system for microlithography with a wall element for thermal shielding or a corresponding projection exposure system, which enables improved image quality.

[0006] This problem is solved by an arrangement according to claim 1, by a projection exposure system according to claim 14, and by the use of an active cooling element according to claim 15. Advantageous embodiments are described in the dependent claims.

[0007] The invention relates to an arrangement comprising a projection system for microlithography and a wall element for thermally shielding the projection system from an illumination system. The projection system comprises an object field that can be illuminated by the illumination system and optical elements for imaging the object field onto an image plane. The wall element comprises a passive shielding surface element arranged in a transition region between a final beam section of the illumination system and a first beam section of the projection system. According to the invention, the arrangement further includes an active cooling element positioned in the transition region, with a cooling surface that extends at least partially along a surface area of ​​the passive shielding surface element.

[0008] First, some terms used in this disclosure are explained. The active cooling element is designed to be actively cooled. In particular, heat energy can be actively extracted from the cooling surface. For example, the active cooling element can have at least one cooling channel for conveying a thermofluid, extending along the cooling surface. The cooling surface of the active cooling element is an outer surface of the active cooling element, which can be oriented towards a heat source, in particular towards the lighting system.

[0009] A lighting system typically comprises multiple optical elements that create a suitable beam path to illuminate the object field of the projection system. The last beam segment of the lighting system refers to the portion of the beam path located between the object plane and the optical element of the lighting system immediately upstream of the object plane. The first beam segment of the projection system refers to the portion of the beam path located between the object plane and the optical element of the projection system immediately downstream of the object plane. The region between the last beam segment of the lighting system and the first beam segment of the projection system is also referred to here as the transition region.

[0010] The passive shielding element is located in the aforementioned transition area. It may have a recess through which the beam path can pass to transition from the lighting system to the projection system. Furthermore, the passive shielding element may be positioned such that an imaginary connecting plane linking the last beam segment of the lighting system with the first beam segment of the projection system intersects the passive shielding element. The passive shielding element serves, in particular, to passively reduce the transfer of radiant heat from the lighting system to the projection system, i.e., without active temperature control.A section of the wall element that serves to separate the lighting system from the projection system and is equipped with means for active cooling (such as cooling channels) is not considered a passive shielding element within the scope of the present disclosure.

[0011] The passive shielding element has a surface area that is significantly larger than its thickness measured perpendicular to this area. The passive shielding element can, in particular, be designed as a sheet metal part. The passive shielding element can be connected to other parts of the wall element. The wall thickness of the passive shielding element can, in one embodiment, be between 0.2 mm and 15 mm, in particular between 0.5 mm and 4 mm.

[0012] In the transition area between the illumination system and the projection system, space is typically limited, as the final beam segment of the illumination system usually strikes the object plane (or a photomask located there, for example) at an acute angle and is reflected. Accordingly, the passive shielding element was regularly designed with a thin material thickness to save space. Since a vacuum or very low pressure is typically maintained within the projection exposure system during operation, it was previously assumed that a thin-walled passive shielding element would be sufficient to adequately reduce the heat transfer mode of thermal radiation that prevails under these pressure conditions. This was considered sufficient, potentially requiring the use of compensation means present in the projection system (i.e., active temperature control of the optical elements).(of the support frame as well as the readjustment of the optical elements) ensures high image quality.

[0013] However, within the scope of the invention, it was recognized that, particularly when using very short wavelengths, the rate of change of the heat flux from the illumination system to the projection system can, under certain circumstances, increase to such an extent that the compensating means present in the projection system can no longer adequately counteract it. Furthermore, it was recognized that the rate of change of the heat flux can be significantly reduced if an active cooling element is positioned in the transition region between the beam path and the passive shielding element, the cooling surface of which extends along the passive shielding element. In particular, due to its orientation along the shielding element, the cooling surface can effectively absorb heat and dissipate it, for example, via a thermofluid conveyed through a cooling channel, thereby significantly reducing the rate of change of the heat flux.In this way, the time constant of heat transfer can be increased to such an extent that possible changes in the position of the optical elements can be sufficiently counteracted by means of active temperature control or readjustment of the positions of the optical elements.

[0014] In one embodiment, the active cooling element is positioned on the side of the passive shielding element facing the projection system. Heat radiation emanating from the passive shielding element can then be effectively absorbed and dissipated by the active cooling element, thus reducing heat input into the optical elements of the projection system. In an alternative embodiment, the active cooling element can also be positioned on the side of the passive shielding element facing the illumination system. In this case, the heat input into the passive shielding element can be reduced, thereby also reducing the rate of change of the heat flux.

[0015] In one embodiment, the active cooling element has at least one cooling channel extending along the cooling surface. In this case, the cooling element can have suitable connections for supplying a thermofluid. It is possible to retrofit an existing projection system by providing an active cooling element. In this case, it is possible to connect existing conveying devices for supplying the thermofluid to the active cooling element.

[0016] Furthermore, the cooling surface can be essentially aligned parallel to the passive shielding element, and in particular, a contour of the cooling surface can be adapted to a contour of the passive shielding element. The features described above enable effective heat absorption and dissipation, thus effectively reducing changes in heat flow. The cooling surface, i.e., the surface of the cooling element facing the heat source, can have an area between 100 cm². 2 and 5000 cm 2 , especially between 600 cm 2 and 1000 cm 2 The thickness of the active cooling element (measured perpendicular to the cooling surface) can be between 2 mm and 20 mm, in particular between 4 mm and 15 mm.

[0017] The cooling surface can, in principle, be in complete or partial thermal contact with at least a portion of the passive shielding element. However, full thermal contact is not mandatory. It may be sufficient if the heat dissipation element is merely positioned adjacent to the passive shielding element. The heat dissipation element can, for example, be attached to the passive shielding element using fasteners.

[0018] The active cooling element can be made of a thermally conductive material, in particular a metal. Furthermore, the active cooling element can have a through-hole aligned along the cooling surface, forming at least part of a cooling channel. Through-holes allow for the creation of multiple cooling channels even in a thin active cooling element, enabling effective cooling of the cooling surface. The active cooling element can, in particular, have at least two through-holes. The through-holes can be fluidly connected to each other by a distribution element in the region of a side face of the active cooling element. A side face is defined as a boundary surface that is at an angle to the cooling surface, where the angle can be substantially 90°. It is also possible that at least one through-hole opening into a side face of the active cooling element serves for the supply or...The system is designed for or used to remove the thermofluid.

[0019] In an alternative embodiment, the active cooling element comprises two surface components having corresponding contours and being joined together over a surface area, wherein at least one of the surface components has an embossed feature such that the embossing between the surface components forms at least a portion of the cooling channel. The surface component facing the direction of the lighting system forms a cooling surface as defined in the present disclosure. The surface components can, in particular, be formed by sheet metal parts. The course of one or more cooling channels can be embossed into at least one of the surface components by a forming process, thereby creating the aforementioned embossed feature. It can be provided that the surface components are welded together along at least a portion of the cooling channel(s).

[0020] Alternatively, the active cooling element can also be manufactured using an additive manufacturing process. Additive manufacturing allows cooling channels to be flexibly integrated into the component.

[0021] When a quantity of thermofluid at a lower temperature than the active cooling element is passed through a cooling channel of the active cooling element, it gradually absorbs heat. This means that its capacity to absorb further heat tends to decrease with the distance traveled within the cooling channel. In principle, this can create an undesirable temperature gradient along the cooling channel. However, this can be counteracted by a suitable choice of the coolant channel's path. In particular, the path of at least one cooling channel can be designed in such a way as to prevent the formation of a temperature gradient. For example, this can be achieved by providing two or more independently fed cooling channels, each running along different sections of the cooling surface.Furthermore, it may be provided that two or more independently fed cooling channels are included, which are designed to distribute the coolant symmetrically within the active cooling element. Finally, it may be provided that at least two independently fed cooling channels with spatially adjacent channel sections are included, through which coolant flows in opposite directions.

[0022] The invention further relates to a projection exposure system comprising an arrangement according to the invention and a lighting system configured to illuminate the object field. The projection exposure system can be further developed by additional features described above in connection with the arrangement according to the invention.

[0023] The invention further relates to the use of an active cooling element within a projection exposure system for microlithography. The projection exposure system comprises an illumination system, a projection system, and a wall element for thermally shielding the projection system from the illumination system. The illumination system is configured to illuminate an object field of the projection system, and the projection system is configured to image the object field onto a plane. The wall element comprises a passive shielding surface element arranged in a transition region between a final beam section of the illumination system and a first beam section of the projection system. According to the invention, the active cooling element is positioned in the transition region such that a cooling surface of the active cooling element extends at least partially along a surface area of ​​the passive shielding surface element.The use can be further developed by additional features described above in connection with the arrangement according to the invention.

[0024] The invention is described below by way of example with reference to the accompanying drawings and advantageous embodiments. The drawings show: Fig. 1: an embodiment of a projection exposure system according to the invention; Fig. 2: an enlarged section from the Fig. 1; Fig. 3: a side view of the side of the wall element facing the projection system of the embodiment of Fig. 1; Fig. 4: A transparent three-dimensional view of the active cooling element of the embodiment of the Fig. 1; Fig. 5: a cross-sectional view along the in the Fig. 3 and Fig. 4 drawn lines AA; Fig. 6: a side view of the side of an alternative active cooling element facing the projection system; Fig. 7: a cross-sectional view along the line in the Fig. 6 drawn lines BB; Fig. 8: a graphical representation of the results of theoretical calculations to illustrate the advantages of the invention.

[0025] In Fig. Figure 1 schematically illustrates a microlithographic EUV projection exposure system according to the invention. The projection exposure system comprises an exposure beam source 14, an illumination system 10, and a projection system 22, which are operated together in a vacuum chamber 23.

[0026] The exposure source 14 generates electromagnetic radiation in the EUV range, specifically with a wavelength between 5 nm and 30 nm. The exposure radiation emitted by the exposure source 14 is focused by a collector 15 into an intermediate focal plane 16. Exposure radiation passing from the intermediate focal plane 16 is directed by the illumination system 10 into an object plane 12, so that an object field in the object plane 12 is illuminated with uniform radiation intensity.

[0027] The illumination system 10 comprises a deflecting mirror 17, which deflects the illumination radiation onto a first faceted mirror 18. A second faceted mirror 19 is arranged downstream of the first faceted mirror 18. The facets of the first faceted mirror 18 are imaged onto the object plane 12 by the second faceted mirror 19. The portion of the beam path located between the faceted mirror 19 and the object field is also referred to here as the final beam segment of the illumination system 10.

[0028] In the object plane 12, a photomask 13 is arranged, which is imaged onto an image plane 21 via a plurality of mirrors M1-M6 of the projection system 22. The part of the beam path located between the object field and the first mirror M1 of the projection system 22 is also referred to here as the first beam section of the projection system 22.

[0029] A structure formed on the photomask 13 is transferred to a radiation-sensitive layer of a wafer 20 arranged in the image plane 21 by means of mirrors M1-M6. The photomask 13 is suspended from a first scanning device 24, and the wafer 20 rests on a second scanning device 25, so that the wafer 20 can be exposed in a single scanning operation in which the photomask 13 and the wafer 20 are moved synchronously. The photomask 13 can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and particularly preferably 1:1 or 1:2. The photomask 13 can be substantially rectangular. The photomask 13 can preferably be 5 to 7 inches long and wide, and particularly preferably 6 inches long and wide. Alternatively, the photomask can be 5 to 7 inches long and 10 to 14 inches wide, preferably 6 inches long and 12 inches wide.

[0030] In the Fig. In the example shown, the projection system 22 comprises six mirrors M1-M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors are also possible. The penultimate mirror M5 and the last mirror M6 each have an aperture for the illumination radiation, making the projection system 22 a doubly obscured optical system. The projection system 22 has an image-side numerical aperture greater than 0.3, and which can also be greater than 0.6, for example, 0.7 or 0.75.

[0031] The projection system 22 can in particular be anamorphic, i.e. it has in particular different image scales β x , β y in the x and y directions. The two image scales β x , β y of the projection system 20 are preferably located at (β x , β y) = (+ / - 0.25, / +- 0.125). A magnification β of 0.25 corresponds to a reduction in the ratio of 4:1, while a magnification β of 0.125 results in a reduction in the ratio of 8:1. A positive sign for the magnification β indicates a magnification without image inversion, a negative sign indicates a magnification with image inversion.

[0032] The reflective surfaces of mirrors M1-M6 can be designed as freeform surfaces without an axis of rotational symmetry. Mirrors M1-M6, like the mirrors of the illumination system 10, can have reflective coatings for the illumination radiation. These reflective coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon. Despite the highly reflective coatings of the mirrors, a considerable proportion (e.g., 30%) of the illumination radiation is absorbed by the mirrors and converted into heat. This leads, in particular, to a high heat input into mirrors 17, 18, and 19 of the illumination system. To prevent this heat from transferring unhindered into the projection system 22, a barrier is installed between the illumination system 10 and the projection system 22. Fig. 1 Wall element 28, indicated only schematically by a dashed line, which serves for thermal shielding.

[0033] Fig. Figure 2 shows an enlarged section of the Fig. Figure 1, where the wall element 28 is shown in a schematic cross-section and in greater detail. In this view, it can be seen that the wall element 28 has a lower wall section 29 and a passive shielding element 30 attached to it. The shielding element 30 is arranged between the last beam section 41 of the illumination system 10 and the first beam section 42 of the projection system and has a recess 40 through which the beam path can pass. In the area between the beam sections 41 and 42, the installation space is limited because the beam path strikes the photomask 13 at an acute angle and is reflected. A minimum distance between the mirror M1 and an edge of the last beam section 41 is approximately 60 mm (measured perpendicular to the shielding element 30). Since the beam sections 41 and 42 taper towards the object plane 12, this distance decreases towards the object plane 12.The passive shielding surface element 30 is designed with a low material thickness of 3 mm and is made of aluminium.

[0034] On the side of the passive shielding element 30 facing the projection system 22, an active cooling element 31 is located and attached to the shielding element 30. The active cooling element 31 is made of stainless steel and has a thermal conductivity of 20 W / (mK). A cooling surface of the active cooling element 31 is in contact with a corresponding counter surface of the passive shielding element 30. The active cooling element 31 is permeated with cooling channels (in Fig. 2 (not shown), which extend along the cooling surface. The cooling surface has an area of ​​approximately 74 cm². 2 The thickness of the active cooling element 31, measured perpendicular to the cooling surface, is approximately 7.5 mm.

[0035] Fig. Figure 3 shows a side view of the side of the wall element 28 of the embodiment facing the projection system 22. Fig. 1. In this view, it can be seen that the active cooling element 31 is attached to the passive shielding element 30 by means of fastening elements 34.

[0036] Fig. Figure 4 shows a transparent three-dimensional view of the active cooling element 31 of the embodiment of the Fig. 1. The active cooling element 31 has a convex central section and two flat side sections. Each side section has three through-holes 45 through which fastening elements for attaching the active cooling element to the passive shielding element 30 can be passed. A plurality of through-holes extend along a vertical direction of the active cooling element 31, each forming sections of cooling channels 35, 35', 35''. In the region of the upper and lower side surfaces 39 of the active cooling element 31, several of the through-holes are fluid-connected to each other by means of distribution elements 38, 38' embedded in the active cooling element 31. The active cooling element also has several fluid connections 33, 33', 33'', 34, 34', 34'' to which fluid lines for supplying or removing a thermal fluid can be connected.

[0037] For example, a thermofluid can be supplied via port 33, which is guided through the two bores connected to port 33 to the distribution element 38 and from there through two further bores to be discharged again via fluid port 34. A first cooling channel 35, formed by the bores and the distribution element 38, extends between fluid ports 33 and 34. Similarly, within the curved central section, a second cooling channel 35' extends from port 33' via the associated bores and the distribution elements 38' to fluid port 34'. Finally, a third cooling channel 35'' (essentially symmetrical to the first cooling channel 35) extends from fluid port 33'' to fluid port 34''.The three cooling channels 35, 35', 35'' mentioned above are supplied independently with a thermofluid, each running only through a section of the cooling element 31 and are therefore correspondingly shorter. Furthermore, there are sections of the cooling channels 35 and 35'', and of the cooling channels 35' and 35'', in which the thermofluid flows in the opposite direction. This reduces the temperature gradient that would otherwise arise along the cooling channels within the cooling element 31.

[0038] The Fig. 5 shows a cross-sectional view along the [unclear] in the Fig. 3 and Fig. 4 drawn lines AA. In the Fig. 4 and Fig. Figure 5 shows that the passive shielding element 30 also has a curvature in a central section, whereby a contour of the active cooling element or its cooling surface 32 is adapted to a contour of the passive shielding element 30. The cooling surface 32 is in full thermal contact with the passive shielding element 30.

[0039] The active cooling element 31 effectively removes heat from the passive shielding element 30. This limits the rate of change of the heat flow from the lighting system to the projection system during operation of the projection exposure system.

[0040] Fig. Figure 6 shows a side view of an alternative active cooling element 31, which can be used in an alternative embodiment of the invention. Fig. Figure 7 shows a cross-sectional view along the in Fig. Figure 6, line BB. In this embodiment, the active cooling element 31 comprises two surface components 36, 37, each formed by metal sheets. The surface component 36 has two cooling channels 35 embossed into it. Apart from the areas formed by the embossing, the two surface components 36, 37 have corresponding contours, so that two cooling channels 35 are formed between the surface components 36, 37 when they are placed on top of each other. The surface components 36, 37 are welded together along the cooling channels. Fluid connections 33, 34 are also provided for supplying and removing a thermal fluid. The surface of the surface component 37 facing away from the surface component 36 forms a cooling surface that can be brought into thermal contact with a counter surface of a suitable passive shielding element to form an arrangement according to the invention.

[0041] In this embodiment as well, the cooling channels 35 each extend over a section of the active cooling element 31, wherein the two cooling channels 35 are essentially symmetrically aligned with respect to a vertical axis of symmetry.

[0042] Within the scope of the invention, theoretical calculations were carried out using FEM simulation to simulate the effects of an active cooling element on the heat flow that passes from the lighting system to the projection system within an exemplary projection exposure system. Fig. Figure 8 shows the results of these calculations. In particular, the normalized heat flow is shown. Q˙=dQdt, The transition from the lighting system to an optical element of the projection system in the example system is shown over time, with the time axis also normalized. A warm-up phase, which is irrelevant for the present analysis, is not shown.

[0043] Graph 52 illustrates the heat flow that results when the optical element of the projection system is shielded from the heat source solely by a passive shielding element without an active cooling element. Graph 53 shows the heat flow that results when an active cooling element is used according to the invention, as shown in the Fig. 1 and Fig. Figure 2 shows the position between the passive shielding element and the first beam section of the projection system. The normalization factor used corresponds to the maximum heat flow achieved when no active cooling is used (Graph 52).

[0044] Graph 52 initially shows a steep increase in heat flow (see line 54) until it eventually approaches its maximum asymptotic value. When an active cooling element is present (graph 53), the heat flow exhibits a fundamentally similar time profile, although the maximum heat flow is significantly lower than in graph 52. In particular, the active cooling element can also significantly reduce the maximum rate of change of the heat flow, indicated by the slope of the dashed lines 55. By limiting the rate of change of the heat flow, potential positional changes of the optical elements within the projection system can be adequately counteracted using the available active temperature control or readjustment of the optical element positions, thus ensuring high image quality.

Claims

[1] Arrangement comprising a projection system (22) for microlithography and a wall element (28) for thermal shielding the projection system (22) from an illumination system (10), wherein the projection system (22) has an object field illuminable by the illumination system (10) and optical elements (M1 - M6) for imaging the object field onto an image plane (21), wherein the wall element (28) has a passive shielding surface element (30) arranged in a transition area between a last beam section (41) of the illumination system (10) and a first beam section (42) of the projection system (22), characterized by , that the arrangement further comprises an active cooling element (31) positioned in the transition area with a cooling surface (32) which extends at least partially along a surface extent of the passive shielding surface element (30). [2] Arrangement according to claim 1, characterized by, that the active cooling element (31) is positioned on the side of the passive shielding element (30) facing the projection system (22). [3] Arrangement according to one of claims 1 to 2, characterized by that the cooling surface (32) is oriented substantially parallel to the passive shielding surface element (30), wherein preferably a contour of the cooling surface (32) is adapted to a contour of the passive shielding surface element (30). [4] Arrangement according to any one of claims 1 to 3, characterized by , that the cooling surface (32) is in thermal contact with at least a partial surface of the passive shielding element (30). [5] Arrangement according to claim 4, characterized by , that the cooling surface (32) has an area between 100 cm 2 and 5000 cm 2 lies. [6] Arrangement according to claim 4 or 5, characterized by that the active cooling element has a thickness between 2 mm and 30 mm. [7] Arrangement according to any one of claims 1 to 6, characterized by , that the active cooling element (31) is attached to the passive shielding element (30). [8] Arrangement according to any one of claims 1 to 7, characterized by , that the active cooling element (31) has at least one through-hole extending along the cooling surface (32), which forms at least part of a cooling channel (35). [9] Arrangement according to claim 8, characterized by , that the active cooling element (31) has at least two through-holes, wherein the through-holes in the area of ​​a side surface (39) of the active cooling element (31) are fluidly connected to each other by a distribution element (38). [10] Arrangement according to any one of claims 1 to 7, characterized by, that the active cooling element (31) has two surface components (36, 37) which have corresponding contours and are connected to each other over a surface, wherein at least one of the surface components (36, 37) has an embossing, such that at least part of the cooling channel (35) is formed by the embossing between the surface components (36, 37). [11] Arrangement according to any one of claims 1 to 7, characterized by , that the active cooling element (31) is manufactured by an additive manufacturing process. [12] Arrangement according to any one of claims 1 to 11, characterized by , that the active cooling element (31) has at least one cooling channel (35) extending along the cooling surface (32) of the active cooling element (31). [13] Arrangement according to claim 12, characterized by, that the course of at least one cooling channel (35) is designed in such a way as to counteract the formation of a temperature gradient within the active cooling element (31). [14] Projection exposure system comprising an arrangement according to one of claims 1 to 12 and a lighting system (10) configured to illuminate the object field. [15] Use of an active cooling element within a projection exposure system for microlithography comprising an illumination system (10), a projection system (22) and a wall element (28) for thermal shielding the projection system (22) from the illumination system (10), wherein the illumination system (10) is configured to illuminate an object field of the projection system (22), wherein the projection system (22) is configured to image the object field onto an image plane (21), and wherein the wall element has a passive shielding surface element (30) arranged in a transition area between a last beam section of the illumination system (10) and a first beam section of the projection system (22), characterized by, that the active cooling element (31) is positioned in the transition area such that a cooling surface (32) of the active cooling element (31) extends at least partially along a surface area of ​​the passive shielding surface element (30).

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