Component of an optical system and methods for its manufacture

Abstract

The invention relates to an assembly of an optical system and a method for its manufacture, wherein the assembly comprises a heat sink (100) with fluid channels (104, 204, 404), each of which is permeable to a cooling fluid for the purpose of dissipating heat generated during the operation of the optical system. According to one aspect, the heat sink has at least two segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b), each of which has at least one of the fluid channels (104, 204, 404) in a separate closed cooling circuit.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The invention relates to an assembly of an optical system and a method for its production. State of the art

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure system, which has an illumination device and a projection lens. The image of a mask (= reticle) illuminated by the illumination device is projected by the projection lens onto a substrate (e.g., a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] In projection lenses designed for the EUV range, ie at wavelengths of approximately 13.5 nm or less, mirrors are used as optical components for the imaging process due to the lack of availability of suitable light-transmitting refractive materials.

[0004] In the illumination device of a microlithographic projection exposure system designed for operation in the EUV range, the use of facet mirrors in the form of field facet mirrors and pupil facet mirrors as bundle-guiding components is known, for example from DE 10 2008 009 600 A1. Such facet mirrors are constructed from a plurality of mirror elements or mirror facets, which can each be designed to be tiltable via solid-state joints for the purpose of adjustment or for the realization of certain illumination angle distributions. These mirror facets can in turn comprise a plurality of micromirrors. Furthermore, in an illumination device of a microlithographic projection exposure system designed for operation at wavelengths in the VUV range, for setting defined illumination settings (ieIntensity distributions in a pupil plane of the illumination device) the use of mirror arrangements, e.g. from WO 2005 / 026843 A2, which comprise a plurality of independently adjustable micromirrors.

[0005] A problem that occurs in practice is that the (e.g., EUV) mirrors or mirror elements experience heating and associated thermal expansion or deformation, among other things due to absorption of the radiation emitted by the light source, which in turn can impair the imaging properties of the optical system. Various approaches are known to prevent surface deformations and associated optical aberrations caused by heat input into a (e.g., EUV) mirror, in particular active direct cooling of the mirrors or mirror elements.

[0006] For example, heat dissipation can be achieved via a cooler or heat sink through which a cooling fluid (e.g., cooling water) flows. Such coolers can, in particular, be incorporated directly into the support frame or the components forming this support frame.

[0007] A problem that arises in practice with active cooling of the aforementioned mirrors or mirror elements is that, as the light source power increases, achieving sufficiently efficient heat dissipation while still ensuring high precision of the mirrors or mirror elements presents a demanding challenge. The assembly required for the mechanical mounting and control of the mirror array is highly sensitive to deformation. Thermally induced deformation associated with the heating of the mirror elements by incident electromagnetic radiation, as well as parasitic heat from the electronic components, ultimately leads to tilting of the mirror elements and thus to optical aberrations, which impairs the performance of the optical system or the projection exposure system.

[0008] A particular problem is that the individual components of a heat sink (e.g., sleeves for accommodating cooling fluid channels) are manufactured by turning and milling, for example, and then soldered together. This inherently poses the risk that, over the lifetime of the optical system, corrosion-related leaks will occur in the area of ​​the components in contact with the cooling fluid, or in the solder joints sealing or joining these components. Inspecting these solder joints after the soldering process is difficult. Furthermore, all joints between components through which the cooling fluid flows must be sealed gas-tight by soldering. Furthermore, the applied solder has a sensitive influence on the heat dissipation result.

[0009] As an example, reference is made to US 10,663,873 B2 regarding the state of the art. SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide an assembly of an optical system and a method for its production, which enable process-economical production while at least partially avoiding the problems described in the introduction.

[0011] This object is achieved by the assembly or the method according to the features of the independent patent claims.

[0012] An assembly of an optical system has - a heat sink with fluid channels through which a cooling fluid can flow to dissipate heat generated during operation of the optical system; - wherein the heat sink has at least two segments, each of which has at least one of the fluid channels in a separate closed cooling circuit.

[0013] The invention is based in particular on the concept of realising a segmentation in a heat sink for dissipating heat generated in an optical system in such a way that, on the one hand, process-economical production (and in particular one that combines additive manufacturing processes and joining processes in a suitable manner) is enabled and, on the other hand, sealing problems in the region of the fluid channels through which the cooling fluid flows are avoided. Because the individual segments, which can each be produced using an additive manufacturing process (e.g. 3D printing), have a self-contained cooling circuit, no joining points or soldering seams are required in the region of one and the same fluid channel during the joining process (in particular soldering processes) then used to assemble the heat sink, with the result that the cooling fluid flowing through the respective fluid channels can be cooled without coming into contact with a joining point orThe solder seam remains intact and the occurrence of corrosion damage is reliably avoided.

[0014] According to one embodiment, the heat sink has at least three, in particular at least four segments.

[0015] According to one embodiment, each of the segments is monolithic.

[0016] According to one embodiment, the segments are joined to a base body, in particular soldered, welded, diffusion welded or screwed.

[0017] According to one embodiment, the fluid channels are arranged such that the cooling fluid flowing through them has no contact with a joint.

[0018] The invention further relates to an assembly of an optical system, with - a heat sink with fluid channels through which a cooling fluid can flow to dissipate heat generated during operation of the optical system; - wherein the heat sink has at least two segments, each of which has at least one of the fluid channels; - wherein the segments are joined to a base body; and - wherein the fluid channels are arranged such that the cooling fluid flowing through them has no contact with a joint.

[0019] According to one embodiment, each of the segments has a separate inlet channel and a separate return channel for the cooling fluid.

[0020] According to one embodiment, the inlet channels and the return channels are each located outside a joint, in particular outside a solder seam.

[0021] According to one embodiment, the heat sink has bores for accommodating technical components, in particular interface components.

[0022] The fluid channels present in the heat sink according to the invention for transporting the cooling fluid can be spiral-shaped or designed in another way so that they dissipate the heat as optimally as possible.

[0023] According to one embodiment, each fluid channel is assigned an inlet channel and a return channel, which are located on the same side of the respective fluid channel.

[0024] According to one embodiment, the assembly further comprises a component from which heat generated during operation of the optical system can be dissipated via the heat sink.

[0025] According to one embodiment, this component is an optical element, in particular a mirror array.

[0026] According to one embodiment, the optical element is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm.

[0027] The invention further relates to an optical system, in particular of a microlithographic projection exposure apparatus, wherein the optical system has an assembly with the features described above.

[0028] The invention further relates to a microlithographic projection exposure apparatus with an optical system according to the invention.

[0029] The invention further relates to a method for producing an assembly of an optical system, the method comprising the following steps: - Providing a base body; - Providing a plurality of segments of a heat sink, wherein at least one fluid channel is integrated into each of these segments; and - Joining the segments to the base body.

[0030] According to one embodiment, providing the plurality of segments comprises producing them by additive manufacturing or 3D printing.

[0031] According to one embodiment, the joining comprises a soldering process or welding process or a non-material connection (e.g. by screwing).

[0032] Further embodiments of the invention can be found in the description and the dependent claims.

[0033] The invention is explained in more detail below with reference to embodiments shown in the attached figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] They show: Fig. 1-3 are schematic representations to explain the structure and operation of a heat sink in an exemplary embodiment of the invention; Fig. 4a-4d are schematic representations to explain a possible method for assembling a heat sink according to the invention; Fig. 5-6 are schematic diagrams for explaining an exemplary structure of a conventional heat sink; and Fig. 7 a schematic representation of the possible structure of a microlithographic projection exposure system designed for operation in the EUV as an application example of the assembly according to the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] In the following, an exemplary embodiment of a heat sink in an assembly according to the invention as well as the possible assembly of such a heat sink will be described with reference to the schematic representations of Fig. 1 to Fig. 4d described.

[0036] This heat sink, which can be, for example, a heat sink for a mirror array with a plurality of mirror elements, is characterized in particular by the fact that the segmentation of the heat sink is realized without severing the fluid channels. The fluid channels are arranged in such a way that the cooling fluid flowing through them does not come into contact with a joint (e.g., solder seam, weld seam, or parting line in screwed segments). The mirror elements can be, in particular, MEMS mirrors (= micro-electro-mechanical system) in a microlithographic projection exposure system (for example, with the Fig. 7 shown structure).

[0037] Fig. 1 shows a schematic plan view to explain the possible construction of a heat sink 100 according to the invention as well as the above-mentioned principle underlying the invention. According to Fig. 1, segments 103a, 103b, 103c, 103d are joined to a common base body 101. The number of segments is merely exemplary and may also be smaller or larger than four. The segments 103a, 103b, 103c, 103d each have bores 102, as is known, for example, for accommodating a mirror array with a plurality of mirror elements in the form of microelectromechanical systems (so-called "MEMS mirrors"). The mirror elements may each have an optically effective area of ​​the order of 1 mm, merely exemplary (and without the invention being limited thereto). 2The number of mirror elements of a mirror array can be several hundred (again, without the invention being limited thereto). The dimensions of the segments 103a, 103b, 103c, 103d can be, merely by way of example (and likewise without the invention being limited thereto), on the order of 500 mm * 500 mm or less, whereby such dimensions still enable economical additive manufacturing (via 3D printing) of the segments from a metallic material or a metal alloy (e.g., stainless steel). Furthermore, the segments 103a, 103b, 103c, 103d have fluid channels 104, whereby a separate inlet channel 105a, 105b, 105c or 105d and a separate return channel 106a, 106b, 106c or 106d are connected to each of the aforementioned segments.

[0038] Fig. 2 shows a schematic detailed view to explain an embodiment of the heat sink according to the invention, wherein in comparison to Fig. 1 analogous or essentially functionally identical components are designated by reference numerals increased by “100”.

[0039] According to Fig. 2, each of the segments (of which only two segments, 203a and 203b, are shown) has fluid channels 204, with segment 203a being assigned an inlet channel 205a and a return channel 206a, and with segment 203b being assigned an inlet channel 205b and a return channel 206b. The inlet channel 205a and the return channel 206a, as well as the inlet channel 205b and the return channel 206b, each form a separate, self-contained cooling circuit. The supply and return channels assigned to the individual segments 203a, 203b are not connected to one another and are located on one and the same side of the respective fluid channel or a bore accommodating this fluid channel, so that a separation 207 of the respective segments 203a, 203b or the heat sink is possible without severing or damaging the fluid channels.

[0040] Fig. 5 shows, for comparison, an arrangement of fluid channels with flow and return channels in a conventional heat sink, where, in comparison to Fig. 2 analogous or essentially functionally equivalent components are designated with reference numbers increased by “300”. In contrast to Fig. 2 are in accordance with Fig. 5, the fluid channels 504 are each connected on both sides to an inlet channel 505 and a return channel 506. In particular, the inlet and return channels are interconnected, so that a separation 507 of the heat sink is not possible without severing the fluid channels.

[0041] Fig. 3 shows a schematic vertical sectional view to explain an embodiment of the heat sink according to the invention, wherein in comparison to Fig. 1 analogous or essentially functionally equivalent components are designated by reference numerals increased by “200”.

[0042] According to Fig. 3, each of the segments (of which only segments 303a and 303b are shown) has bores 302 with sleeves 308a, 308b, each of which is assigned an inlet and return channel on one side, with segment 303a being assigned the inlet channel 305a and the return channel 306a, and segment 303b being assigned the inlet channel 305b and the return channel 306b. The design with sleeves 308a, 308b is merely optional and exemplary, although a monolithic design without sleeves is also possible in further embodiments. The inlet channel 305a and the return channel 306a, as well as the inlet channel 305b and the return channel 306b, each form a separate, self-contained cooling circuit. The inlet and return channels of different segments 303a, 303b are not connected to each other, so that a separation 307 of the respective segments 303a, 303b or the heat sink is possible without severing or damaging the fluid channels.

[0043] Furthermore, according to Fig. 3, the segments 303a, 303b are manufactured with integrated fluid channels or inlet and return channels in a monolithic design (3D printing), so that joints (e.g., solder seams) in the area of ​​the fluid-flowing fluid channels of one and the same segment are not required. However, the segments 303a, 303b can be bonded to a base body (as in Fig. 1) are joined in a form-fitting manner (e.g. by screwing) or in a material-fitting manner (e.g. by soldering, welding, diffusion welding or the like).

[0044] Fig. 6 shows a schematic vertical sectional view to explain a possible embodiment of a conventional heat sink, wherein in comparison to Fig. 3 analogous or essentially functionally equivalent components are designated with reference numbers increased by “300”. In contrast to Fig. 3 are in accordance with Fig. 6 inlet channels 605 and return channels 606 are arranged on both sides of bores 602 with sleeves 608. In particular, the inlet and return channels 605, 606 are milled into component plates 610a and 610b, respectively, which are joined (e.g., soldered) in such a way that corrosion damage can occur in the area of ​​the fluid channels at the respective joint 609 (e.g., solder seam).

[0045] Fig. 4a-4d show schematic representations to explain a possible method for assembling a heat sink in an assembly according to the invention, wherein in comparison to Fig. 1 analogous or essentially functionally equivalent components are designated by reference numerals increased by “300”.

[0046] Fig. 4a shows a vertical section of a base body 401 for the heat sink, which is manufactured, for example, by milling.

[0047] Fig. 4b shows a segment 403a with integrated fluid channels 404, which is manufactured monolithically using the 3D printing process.

[0048] Fig. Figure 4c shows, in vertical section, the joining of the base body 401 with the segments (of which only two segments 403a, 403b are shown), whereby the aforementioned segments are joined to the base body 401 via a joint 409, for example, by means of a material fit (by soldering or welding) or a form fit (e.g., by screwing). The separation 407 located between the segments 403a, 403b runs outside the fluid channels 404.

[0049] Fig. Figure 4d shows a vertical section of a redesign of the heat sink, for example by inserting holes 402 to accommodate components (interfaces, components for a MEMS mirror assembly, etc.).

[0050] Fig. 7 shows a schematic representation of the possible structure of a microlithographic projection exposure system designed for operation in the EUV as an application example of the assembly according to the invention.

[0051] According to Fig. 7, the projection exposure system 1 comprises an illumination device 2 and a projection lens 10. One embodiment of the illumination device 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 provided as a module separate from the other illumination device. In this case, the illumination device does not include the light source 3.

[0052] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced via a reticle displacement drive 9, in particular in a scanning direction. Fig. For illustrative purposes, a Cartesian xyz coordinate system is shown in Figure 7. The x-direction is perpendicular to the plane of the drawing. The y-direction is horizontal, and the z-direction is vertical. The scanning direction is in Fig. 7 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0053] The projection lens 10 is used to project the object field 5 into an image field 11 in an image plane 12. A structure on the reticle 7 is projected 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.

[0054] Radiation source 3 is an EUV radiation source. Radiation source 3 emits, in particular, EUV radiation, which is also referred to below as useful radiation or illumination radiation. The useful radiation has, in particular, a wavelength in the range between 5 nm and 30 nm. Radiation source 3 can be, for example, a plasma source, a synchrotron-based radiation source, or a free-electron laser (FEL). The illumination radiation 16 emanating from the radiation source 3 is bundled by a collector 17 and propagates through an intermediate focus in an intermediate focal plane 18 into the illumination optics 4. The illumination optics 4 has a deflection mirror 19 and, downstream of this in the beam path, a first facet mirror 20 (with schematically indicated facets 21) and a second facet mirror 22 (with schematically indicated facets 23).The illumination optics 4 shown is merely an example, and depending on the design, the deflection mirror 19 may be located at a different location or may not be present at all.

[0055] The facet mirrors can be realized in particular in the manner according to the invention, ie can be cooled as a mirror array via a heat sink designed in the manner according to the invention.

[0056] The projection lens 10 has a plurality of mirrors Mi (i= 1, 2, ...), which are numbered according to their arrangement in the beam path of the projection exposure system 1. In the Fig.In the example shown in Figure 7, the projection lens 10 has 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 lens 10 is a doubly obscured optical system. The projection lens 10 has a numerical aperture on the image side that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0057] However, the invention is not limited to application in a projection exposure system designed for operation in the EUV range. In particular, the invention can also be advantageously applied in a projection exposure system designed for operation in the DUV range (i.e., at wavelengths less than 250 nm, in particular less than 200 nm) or in another optical system.

[0058] Although the invention has been described with reference to specific embodiments, numerous variations and alternative embodiments will become apparent to those skilled in the art, e.g., by combining and / or interchanging features of individual embodiments. Accordingly, it will be understood by those skilled in the art that such variations and alternative embodiments are encompassed by the present invention, and the scope of the invention is limited only by the appended claims and their equivalents. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 009 600 A1

[0004] WO 2005 / 026843 A2

[0004] US 10,663,873 B2

[0009]

Claims

[1] Assembly of an optical system, with • a heat sink (100) with fluid channels (104, 204, 404) through which a cooling fluid can flow in each case to dissipate heat generated during operation of the optical system; • wherein the heat sink has at least two segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b), each of which has at least one of the fluid channels (104, 204, 404) in a separate closed cooling circuit. [2] Assembly according to claim 1, characterized by that the heat sink (100) has at least three, in particular at least four segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b). [3] Assembly according to claim 1 or 2, characterized by that each of these segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b) is monolithic. [4] Assembly according to claim 3, characterized bythat the segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b) are joined to a base body (101, 401), in particular soldered, welded, diffusion-welded or screwed. [5] Assembly according to claim 4, characterized by that the fluid channels (104, 204, 404) are arranged such that the cooling fluid flowing through them has no contact with a joint. [6] Assembly of an optical system, with • a heat sink (100) with fluid channels (104, 204, 404) through which a cooling fluid can flow in each case to dissipate heat generated during operation of the optical system; • wherein the heat sink has at least two segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b), each having at least one of the fluid channels (104, 204, 404); • wherein the segments are joined to a base body (101, 401); and • wherein the fluid channels (104, 204, 404) are arranged such that the cooling fluid flowing through them has no contact with a joint. [7] Assembly according to one of the preceding claims, characterized by that each of the segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b) has a separate inlet channel (105a, 105b, 105c, 105d, 205a, 205b, 305a, 305b) and a separate return channel (106a, 106b, 106c, 106d, 206a, 206b, 306a, 306b) for the cooling fluid. [8] Assembly according to claim 7, characterized by that the inlet channels (105a, 105b, 105c, 105d, 205a, 205b, 305a, 305b) and the return channels (106a, 106b, 106c, 106d, 206a, 206b, 306a, 306b) are each located outside a joint, in particular outside a soldering or welding seam. [9] Assembly according to one of the preceding claims, characterized bythat the heat sink (100) has bores for receiving technical components, in particular interface components. [10] Assembly according to one of the preceding claims, characterized by that each fluid channel is assigned an inlet channel (305a, 305b) and a return channel (306a, 306b), which are located on the same side of the respective fluid channel. [11] Assembly according to one of the preceding claims, characterized by that the assembly further comprises a component from which heat generated during operation of the optical system can be dissipated via the heat sink (100). [12] Assembly according to claim 11, characterized by that this component is an optical element, in particular a mirror array. [13] Assembly according to claim 12, characterized by that the optical element is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm. [14] Optical system, in particular of a microlithographic projection exposure system, with an assembly according to one of the preceding claims. [15] Microlithographic projection exposure apparatus with an optical system according to claim 14. [16] A method for manufacturing an assembly of an optical system, the method comprising the following steps: - Providing a base body (101, 401); - Providing a plurality of segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b) of a heat sink (100), wherein at least one fluid channel is integrated into each of these segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b); and - Joining the segments (103a, 103b, 103c, 103d, 203a, 203b, 303a, 303b, 403a, 403b) onto the base body (101, 401). [17] Method according to claim 16, characterized bythat the provision of the plurality of segments comprises their production by additive manufacturing, in particular by 3D printing. [18] Method according to claim 16 or 17, characterized by that the joining comprises a soldering or welding process or a non-material connection, in particular by screwing.

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