Component having a hollow structure, and optical assembly

Abstract

The invention relates to a component, in particular an optical element (Mi) or a structural component part, comprising: a main body (25), which has a hollow structure through which a fluid can flow, which hollow structure has: a plurality of cooling channels (31); a fluid distributor (33); and a fluid collector; the fluid distributor (33) having connection channels (33b) for supplying the fluid to the cooling channels (31), which connection channels open into a common inlet channel (33a) which is connected to an inlet opening (29), and / or in which the fluid collector has connection channels for draining the fluid from the cooling channels (31), which connection channels open into a common outlet channel which is connected to an outlet opening. In one aspect of the invention, the inlet channel (33a) has a flow cross section (A) which decreases starting from a connection channel (33b') adjacent to the inlet opening, and / or the outlet channel has a flow cross section which decreases starting from a connection channel adjacent to the outlet opening.

Description

[0001] Component with a hollow structure and optical arrangement

[0002] Reference to related application

[0003] This application claims priority from German patent application DE102023205652.6 filed on June 16, 2023, the entire disclosure of which is incorporated by reference into this application.

[0004] Background of the invention

[0005] The invention relates to a component, in particular an optical element or a structural component, comprising: a base body having a hollow structure through which a fluid can flow, which has a plurality of cooling channels, a fluid distributor, and a fluid collector, wherein the fluid distributor has connecting channels for supplying the fluid to the cooling channels, which open into a common inlet channel connected to an inlet opening, and / or wherein the fluid collector has connecting channels for discharging the fluid from the cooling channels, which open into a common outlet channel connected to an outlet opening. The invention also relates to an optical arrangement, in particular a lithography system, having at least one such component.

[0006] Current lithography systems feature cooling systems with cooling circuits for the thermal stabilization of components such as optical elements or structural components. Cooling lines for the cooling circuits can be routed in the form of hollow structures through both the base bodies of the optical elements and the base bodies of the structural components. To ensure the highest possible heat dissipation and good controllability of the cooling system (low delay and high precision), a fluid, typically in the form of a coolant, flows through the base bodies of the cooled components, or more precisely, their hollow structures (active cooling). Water is often used as the coolant because it has a high heat capacity compared to other fluids and is very readily available.The flowing fluid also ensures improved heat transfer at the surfaces through which it flows (forced convection) and thereby reduces the time constants of the thermal system.

[0007] In the flow boundary layers between the flowing fluid and the walls of the component, an exchange of momentum takes place. In laminar and steady flow, this acts as a constant force on the flowing component (flow pressure loss). If a critical flow velocity (critical Reynolds number Re; e.g., Re=2300 for pipes) is exceeded, which depends on the local geometric boundary conditions and the inflow and outflow boundary conditions, small disturbances can no longer be damped by the viscosity of the flowing medium, so that a flow disturbance results in persistent periodic and random fluctuations in the flow (turbulence). This turbulence increases the momentum transport from the flow into the body and, depending on the geometry, medium, and flow, can possibly also occur at frequencies that are critical for control purposes (e.g.,for position control of mirrors) in the form of flow-induced vibrations (“Flow-induced Vibrations, FIV”) can unintentionally accelerate the component.

[0008] Flow-induced vibrations are thus generated by turbulence-induced pressure and momentum fluctuations in the fluid flow, and the resulting forces on the walls of the hollow structure or the cooling channels lead to dynamic excitation of the component. Furthermore, up to 10% of the hydrodynamic fluctuations (turbulence) are coupled into acoustic pressure waves, which can propagate upstream at the speed of sound of the cooling fluid and, depending on the geometry of the cooling circuit, can be stored in resonance frequencies (as in organ pipes). Attempts are being made to minimize the generation of flow-induced vibrations by optimizing the flow guidance and keeping flow velocities as low as possible.

[0009] When optimizing fluid flow through a hollow structure, the problem is that the hollow structure is typically manufactured using standard machining processes (grinding, milling, drilling, etc.). Due to manufacturing limitations, such manufacturing processes often result in geometries that are not ideal for flow in terms of turbulence generation, acoustics, and the resulting force excitations. This also applies to the fluid distributor or fluid collector.

[0010] The fluid distributor and the fluid collector are generally arranged spatially separate from one another. The fluid distributor serves to divide the fluid flow or the fluid from the inlet opening into the plurality of cooling channels, while the fluid collector serves to combine the fluid flows from the plurality of cooling channels to the outlet opening. For this purpose, the fluid distributor and the fluid collector have a plurality of branches at which the fluid is distributed among the cooling channels. It is possible for the fluid distributor and / or the fluid collector to have branches that form a tree structure. In a tree structure, at least one of several branches formed at a first branch is divided again into two or more branches at a second branch.In the component described here, the fluid distributor has connecting channels to connect one or a group (two or more) of cooling channels to an inlet channel that communicates with an inlet opening and / or the fluid collector has connecting channels to connect one or a group (two or more) of cooling channels to an outlet channel that communicates with an outlet opening.

[0011] The inlet channel and the outlet channel typically have the shape of cylindrical cavities, since such cavities are easily manufactured by milling or drilling. A mirror for a lithography system, which has a fluid distributor in the form of an inlet channel and a fluid collector in the form of an outlet channel, which are designed as cylindrical bores, is described in WO 2022 / 008155 A1. The connecting channels, referred to as distributor channels / collector channels in WO 2022 / 008155 A1, each open vertically into the inlet channel and the outlet channel, respectively, and are also manufactured in the form of bores. The design of the hollow structure described therein, produced using conventional manufacturing methods, is not optimized with regard to minimizing the generation of turbulence.

[0012] However, especially in components for EUV lithography systems, only minimal flow-induced vibrations can be tolerated: The maximum permissible forces generated by flow-induced vibrations are typically in the order of mN up to pN.

[0013] Object of the invention

[0014] The object of the invention is to provide a component and an optical arrangement with at least one such component in which the generation of flow-induced vibrations is reduced.

[0015] Subject of the invention

[0016] This object is achieved according to a first aspect in that the inlet channel has a flow cross-section which decreases starting from a connecting channel adjacent to the inlet opening (in the longitudinal direction of the inlet channel), and / or in that the outlet channel has a flow cross-section which decreases starting from a connecting channel adjacent to the outlet opening (in the longitudinal direction of the outlet channel).

[0017] For the sake of simplicity, it is assumed below that the hollow structure is symmetrical with respect to the fluid distributor and the fluid collector, i.e., that the fluid distributor and the fluid collector have an identical geometry. Accordingly, only the fluid collector or the inlet channel is described below, and it is assumed that what is said for the fluid distributor also applies to the fluid collector. However, this is not necessarily the case, i.e., the fluid distributor and the fluid collector can fundamentally have different geometries that are optimized for the respective flow conditions (e.g., flow direction, swirl, widening / tapering, etc.).A different geometry can be advantageous because the flow conditions in the fluid distributor and the fluid collector differ considerably due to their different functionalities: The fluid distributor serves to distribute the fluid to the cooling channels, which should be as even and turbulence-free as possible. The fluid collector serves to collect the fluid. As the fluid flows out of the cooling channels, which have a small diameter, into the connecting channels, which are usually arranged perpendicular to the cooling channels, and from a respective connecting channel into the outlet channel of the fluid collector, turbulent flows - subject to FIV - can arise due to diameter jumps and shear. This fact may require different design solutions for the fluid collector than for the fluid distributor.

[0018] The inventors have recognized that an inlet channel with a cylindrical geometry is unfavorable with regard to the generation of turbulence or flow-induced vibrations of the fluid collector. Due to the fact that several connecting channels branch off from the inlet channel in the longitudinal direction of the inlet channel, each of which receives a portion of the volume flow, a decreasing volume flow in the inlet channel occurs, starting from the connecting channel adjacent to the inlet opening in the longitudinal direction of the inlet channel. This decreasing volume flow can lead to flow separation in the inlet channel and thus to turbulent and / or periodic fluctuating movements (exponential gradient of the flow velocity in the inlet channel). Turbulent flows can also develop in the connecting channels that open into the inlet channel.

[0019] It is therefore proposed to adapt the flow cross-section in the inlet channel (or in the outlet channel) to the decrease in velocity (and pressure gradient) in order to reduce turbulence generation. It is not absolutely necessary for the flow cross-section to decrease strictly monotonically over the entire length of the inlet channel or the outlet channel. For the purposes of this application, a decrease in the flow cross-section means that the inlet channel (or the outlet channel) can also have sections with a constant flow cross-section. Overall, however, the flow cross-section of the inlet channel or the outlet channel decreases from the connecting channel adjacent to the inlet opening or the outlet opening to the end of the inlet channel (or the outlet channel).

[0020] The reduction in flow cross-section can be achieved in various manufacturing processes. Conventional manufacturing processes, such as milling or drilling, can be used to achieve this. However, it is also possible to create an inlet channel with a decreasing flow cross-section using innovative, alternative manufacturing processes that do not involve standard mechanical machining processes (grinding, milling, drilling, etc.), which severely limit the manufacturable geometry of the hollow structure (see above). Alternative manufacturing processes fundamentally make it possible to create a hollow structure with almost any, possibly complex, geometry in the base body. Therefore, alternative manufacturing processes can be used to create hollow structures optimized with regard to fluid flow and flow-induced vibrations.The alternative manufacturing process can be, for example, selective laser etching or back-side laser ablation.

[0021] In selective laser etching, light in the form of ultrashort pulsed laser radiation (ps or fs pulses) is focused into the volume of a transparent workpiece or substrate. The pulse energy is absorbed only within the focal volume by multiphoton processes. In the focal volume, the transparent material, crack-free or possibly with microcracks, undergoes a change in its optical and chemical properties in such a way that it becomes selectively chemically etchable. By moving the focal volume within the material, contiguous volume regions are modified, which can subsequently be removed using wet-chemical etching. In wet-chemical etching, the substrate is typically immersed in an etching solution for several weeks or months, which preferentially (selectively) releases the modified material.By moving the focus volume within the workpiece, hollow structures of any geometry can be produced using selective laser etching, as described, for example, in WO2021115643 A1.

[0022] In back-side laser ablation, light in the form of ultrashort pulsed laser radiation (ps or fs pulses) is focused into the volume of a transparent workpiece or substrate. In contrast to selective laser etching, the material of the substrate is directly ablated using correspondingly high pulse energies to create the hollow structure. As with selective laser etching, back-side laser ablation exploits the transparency of materials in the form of conventional glasses such as fused silica, borosilicate glass, or titanium-doped fused silica (ULE®) to laser radiation with wavelengths in the visible (VIS) to near-infrared range. Only when the intensity of the laser pulses is high enough can energy be deposited in the material through multiphoton absorption.This makes it possible to focus the laser pulses onto the back of the material with virtually no loss or distortion, so that the laser pulses are only absorbed in the area close to the focus on the back and material removal can take place.

[0023] Methods for material removal by laser ablation starting from the back of a workpiece or a base body are described, for example, in the article “Three-dimensional hole drilling of silica glass from the rear surface with femtosecond laser pulses”, Y. Li et al., Optics Letters Vol. 26(23), pages 1912-1914 (2001), in the article “Precision glass machining, drilling and profile cutting by short pulse lasers”, S. Nikumb et al., Thin Solid Films, Vol. 477(1-2), pages 216-221 (2005) or in the article “Water-assisted femtosecond laser ablation for fabricating three-dimensional microfluidic chips”, Yan Li, Shiliang Qu, Current Applied Physics, Vol. 13, Issue 7, 2013, pages 1292-1295.

[0024] Depending on the manufacturing process used, the reduction in the flow cross-section can be stepwise (possibly with conventional manufacturing processes) or continuous, which can be achieved by alternative manufacturing processes or possibly also by conventional manufacturing processes.

[0025] Preferably, the flow cross-section of the inlet channel decreases linearly in the longitudinal direction of the inlet channel and / or the flow cross-section of the outlet channel decreases linearly in the longitudinal direction of the outlet channel. In order to approximate the essentially constant decrease in the flow velocity of the fluid in the longitudinal direction of the inlet channel due to the connecting channels that open into the inlet channel, it is advantageous if the flow cross-section of the inlet channel decreases linearly in the longitudinal direction starting from the inlet opening. Such a linear decrease is advantageous due to the gradual reduction of the volume flow at the respective distribution channels, in each of which a portion of the volume flow is diverted from the inlet channel.

[0026] A linear decrease in the flow cross-section in the longitudinal direction of the inlet channel is understood to mean that for a plurality of positions yi in the longitudinal direction y of the inlet channel, which corresponds at least to the number of connecting channels, the associated flow cross-section Ai(yi) satisfies a straight line equation, ie the following applies:

[0027] Aj(yi) = Ao - const, yi .

[0028] The linear decrease in the flow cross-section in the longitudinal direction of the inlet channel can occur continuously or in steps (see below). In the first case, the inlet channel does not have any jumps in the flow cross-section. In this case, the above equation can be satisfied for all positions in the longitudinal direction of the inlet channel. However, it is also possible for the above equation to be satisfied only for a plurality of positions, which, for example, do not necessarily correspond to the number of connecting channels, with a respective position yi being assigned to one of the connecting channels. Between these positions yi, the flow cross-section in this case deviates (slightly) from the above equation. For the purposes of this application, the longitudinal direction of the inlet channel is understood to be a line along which the connecting channels open into the inlet channel on the circumferential wall of the inlet channel.The longitudinal direction is therefore not the direction in which the centers of the flow cross-sections of the inlet channel lie.

[0029] Alternatively, it is possible for the flow cross-section to decrease linearly in several stages, with each stage typically being associated with the orifice of a respective connecting channel. By reducing the flow cross-section in stages, a linear decrease in the flow cross-section in the longitudinal direction of the inlet channel can be approximately realized (at the respective stages). In this case, the positions yi at which the above equation is satisfied typically correspond to the locations where a respective stage is located.

[0030] In one embodiment, the inlet channel and / or the outlet channel has / have a circular flow cross-section. For the case described above in which the flow cross-section decreases linearly starting from the inlet opening / the outlet opening, the decrease in the flow cross-section A can be described directly via its radius R, i.e., the flow cross-section A is proportional to R. 2 , i.e. A ~ R 2. Accordingly, a parabolic profile (or a root profile) results for the local radius R in the longitudinal direction of the inlet duct. As described above, a linear or stepped decrease in the flow cross-section can occur. In particular, the root profile can be assumed only at certain support points or at a plurality of positions in the longitudinal direction of the inlet duct, and between these positions the root profile can be approximated by linearly interpolated sections. Simulations have shown that when using the circular inlet duct described above with a linearly decreasing flow cross-section, a reduction in the FIV of between 30% and 90% is possible compared to an inlet duct with a circular flow cross-section and a constant radius R. The linear decrease in the flow cross-section thus enables a significant reduction in flow-induced vibrations.A further reduction of the flow-induced vibrations can be achieved by an iterative optimization of the flow cross-section, which starts from the linear decrease of the flow cross-section described here as the starting configuration.

[0031] In a further embodiment, the inlet channel and / or the outlet channel have a rectangular flow cross-section or a rectangular cross-sectional partial area, wherein preferably a width of the rectangular flow cross-section or of the rectangular cross-sectional partial area is constant and a height of the rectangular flow cross-section or of the rectangular cross-sectional partial area decreases, in particular decreases linearly.

[0032] The longitudinal directions of the connecting channels typically run in a common plane, in which the longitudinal direction of the inlet channel also runs. The width of the rectangular flow cross-section or of the cross-sectional area is measured perpendicular to this plane, and the height of the cross-section is measured in this plane. The constant width of the flow cross-section or of the cross-sectional area ensures that there is no jump in diameter at the transition between the inlet channel and a respective connecting channel, as would be the case if the width of the flow cross-section or of the cross-sectional area were to also decrease. For the constant (linear) decrease in the flow cross-section, in the case of a constant width b of the flow cross-section, a particularly simple relationship results between the flow cross-section A (orits area) and the height h of the flow cross-section in the form of a linear function between the area A and the height h, ie the following applies: A ~ h (at least at the plurality of positions in the longitudinal direction of the inlet channel or the outlet channel described above). The flow cross-section of the inlet channel or the outlet channel can, in principle, have any desired geometry. The flow cross-section can, in particular, be composed of two or more cross-sectional sub-regions having a predetermined geometry. Such a cross-sectional sub-region can, for example, have the rectangular geometry described above.

[0033] In a further development of the above embodiment, the inlet channel and / or the outlet channel have a flow cross-section that is composed of the rectangular cross-sectional region and a semicircular cross-sectional region. The semicircular cross-sectional region typically borders the side of the rectangular cross-sectional region with the constant width. The diameter of the semicircular cross-sectional region corresponds to the width of the rectangular cross-sectional region. This ensures that the width of the flow cross-section remains constant over the length of the inlet channel or the outlet channel and that there is no jump in diameter at the transition to the connecting channels. The flow cross-section described here is advantageous from a manufacturing perspective and can be realized, for example, using a combination of milling and drilling.

[0034] In a further embodiment, the inlet channel and / or the outlet channel have a flow cross-section that is annular. The annular flow cross-section forms an annular gap, wherein the outer circumference of the annular flow cross-section is typically constant and the inner circumference increases, starting from the connecting channel adjacent to the inlet opening or the outlet opening, in order to realize the decreasing flow cross-section. The annular flow cross-section can be a round flow cross-section with an outer radius and an inner radius. However, the annular flow cross-section can also be a rectangular ring or a free-form cross-section, provided that the reduction in cross-section can be suitably realized in terms of manufacturing technology. In this case, too, a linear decrease in the flow cross-section in the longitudinal direction of the inlet channel orThe exhaust channel can be realized by appropriately selecting the ratio of outer radius to inner radius or outer circumference to inner circumference. The annular flow cross-section also has the advantage that an additional boundary layer forms within the flow on the inside of the annular gap, which stabilizes the flow and reduces the tendency of the flow to separate.

[0035] The annular flow cross-section can be realized by removing material from the base body in a ring shape. However, it is also possible to form the annular flow cross-section by introducing an additional component into, for example, a cylindrical inlet channel. The additional component is designed in the manner of a rod with a conical geometry whose cross-section increases with increasing distance from the inlet opening or outlet opening through which it is introduced into the base body. The additional component is fixed in the inlet channel, for example by attaching it to a fluid line or to an adapter of a fluid line that is connected to the inlet opening.

[0036] In a further embodiment, an opening cross-section of a respective connecting channel of the fluid distributor decreases starting from the connecting channel adjacent to the inlet opening, and / or an opening cross-section of a respective connecting channel of the fluid collector decreases starting from the connecting channel adjacent to the outlet opening. This embodiment is particularly advantageous in combination with the embodiment described above, in which the diameter of the flow cross-section decreases starting from the connecting channel adjacent to the inlet opening or the outlet opening, since in this case, a significant cross-sectional jump can occur at the transition between the inlet channel or the outlet channel and the respective connecting channels, especially if these are far away from the inlet opening or the outlet opening.To avoid the cross-sectional jump and the associated flow-induced vibrations, the opening cross-section of each connecting channel, or more precisely, its opening diameter, is adapted to the local diameter of the flow cross-section of the inlet channel or the exhaust channel at the position in the longitudinal direction where the connecting channel opens. To reduce FIV, it is particularly advantageous in this case if the flow cross-section of each connecting channel decreases with increasing distance from the cooling channels (see below).

[0037] In a further embodiment, the connecting channels have a flow cross-section that decreases with increasing distance from the cooling channels. This embodiment is particularly advantageous in combination with the embodiment described above, in which the opening cross-section of the connecting channels varies. In this case in particular, it has proven advantageous if the flow cross-section of the connecting channels is not constant, but rather adapted to the respective opening cross-section.

[0038] In a further development of this embodiment, the connecting channels are conical, with an opening angle of the conical connecting channels preferably being less than 8°. In this case, the connecting channels generally have a circular cross-section. The choice of opening or flank angle depends on the local flow velocity or the local flow profile. Assuming identical flow cross-sections of the connecting channels at the transition to the cooling channels, in the embodiment described above, in which the mouth cross-section of the connecting channels decreases with increasing distance from the inlet opening or outlet opening, the opening angle of the connecting channels increases with increasing distance from the inlet opening or outlet opening.

[0039] In a further embodiment, the flow cross-section of the inlet channel and / or the outlet channel decreases in stages. As described above, a linear or constant cross-section decrease can be approximated even with a stepped decrease in the flow cross-section. The greater the number of steps, the smaller the change in the flow cross-section at each step is as a rule. Excessive changes in the flow cross-section (> 5% relative to the larger flow cross-section at the step) should be avoided in order to prevent local flow separation. As described above, the respective stepped decreasing flow cross-section can be circular, rectangular, a combination of both, or annular, for example. The stepped decrease in the flow cross-section enables or simplifies production using conventional manufacturing processes, albeit with increased complexity.

[0040] It is possible to individually adapt the flow cross-section of the inlet channel or the outlet channel to the respective flow conditions or boundary conditions in a manner other than that described above. As described above, it is not absolutely necessary for the flow cross-section of the inlet channel and the outlet channel as well as the connecting channels to be circular. All types of cascading (stepped change) or diameter design which do not result in a flow cross-section that is constant over the length can be considered here. A second aspect of the invention relates to a component of the type mentioned above, in which the inlet channel has a constant flow cross-section and / or in which the outlet channel has a constant flow cross-section, and in which at least two of the connecting channels each have a different flow cross-section.To counteract flow separation in the inlet channel or outlet channel due to the pressure gradient and the decrease in volume flow (see above), the volume flow discharge from the inlet channel or into the outlet channel can also be controlled via the connecting channels. The counterpressure or volume flow discharge can be influenced via the flow cross-section of the connecting channels. The aim in this case, too, is to keep the pressure gradient in the inlet channel or outlet channel as constant as possible. Since this depends not only on the static pressure distribution (volume flow distribution) but also on the dynamic properties of the flow, no clear geometric or analytical relationship in the form of a calculation rule can be specified for the aspect of the invention described here.Rather, in this case it is necessary to find a suitable relationship through an iterative approach (e.g. through a simulation).

[0041] In general, the second aspect of the invention can lead to interactions within the flow between the inlet channel or the outlet channel and the distribution channels. It should be noted that smaller cross-sections potentially lead to higher flow velocities. This can increase both turbulence and the tendency to separate at sharp edges and transitions. This interaction must be considered as a whole in order to be able to evaluate the desired positive effect. In the first aspect of the invention described above, at least two of the connecting channels can each have a different flow cross-section, i.e. it is not absolutely necessary, i.e. the flow cross-section of the connecting channels can also vary if the flow cross-section of the inlet channel or the outlet channel decreases.

[0042] In a further embodiment, which can be combined with the first aspect described above or with the second aspect of the invention, a flow cross-section of the connecting channels increases starting from a connecting channel adjacent to the inlet opening or starting from a connecting channel adjacent to the outlet opening. The increase in the flow cross-section is understood to mean that the flow cross-section of the connecting channels increases over the length of the inlet channel or over the entire length of the outlet channel. A connecting channel that is further away from the inlet opening than an adjacent connecting channel has at least the same flow cross-section as the adjacent connecting channel. The connecting channel furthest away from the inlet opening / outlet opening has the largest flow cross-section.By increasing the flow cross-sections of the connecting channels, a similar effect can be achieved as by decreasing the flow cross-section of the inlet channel or the outlet channel starting from the inlet opening or the outlet opening, respectively. Both measures can be combined, but this is not mandatory. The following assumes that the flow cross-section of each connecting channel is constant. If this is not the case, the flow cross-section is generally understood to be the cross-section averaged over the length of the connecting channel.

[0043] In a further embodiment, the flow cross-section of at least two, preferably at least three adjacent connecting channels is the same size. It is possible to divide the connecting channels into groups of adjacent connecting channels with the same flow cross-sections. For example, two, three or four connecting channels can belong to such a group. It has been shown that, with a suitable design, a reduction in FIV in the order of approximately 10%-50% is possible in this way. The configuration described here can, if necessary, also form the starting point for simulations to further optimize the flow guidance. It is also possible to specify the flow cross-section of a respective connecting channel or of all connecting channels individually. In particular, all connecting channels can have a different flow cross-section.The decisive factor is the resulting geometrically determined and the dynamic (local) pressure loss in the respective connecting channel, which determines the pressure gradient in the inlet channel or in the outlet channel.

[0044] In a further embodiment, at least one connecting channel has a conical section at the transition to the cooling channels. The conical section is intended to enable flow guidance at the transition to the cooling channels without any cross-sectional jumps. This can be particularly advantageous if a respective connecting channel serves to supply the fluid to two or more cooling channels, as described, for example, in WO 2022 / 008155 A1 cited at the beginning, which is incorporated into this application in its entirety by reference. For this purpose, WO 2022 / 008155 A1 proposes using a stepped bore with a larger bore diameter at the transition to the cooling channels. Instead of the section with the larger bore diameter, the conical section is used in the present application in order to avoid a corresponding cross-sectional jump.

[0045] It is not mandatory for all connecting channels to have a conical section; rather, the number, dimensions, and position of the conical sections can vary to prevent flow separation. When determining the flow cross-section of the connecting channels described above, the conical sections are not taken into account. The same dimensioning rules apply to the opening angle of the conical sections as for the conically shaped connecting channels described above (opening angle < 8°).

[0046] Based on an ideally, but not necessarily, symmetrical basic geometry, whereby the global pressure loss is largely dominated by the cooling channels and thus, for parallel structures, the cooling medium can be assumed to be approximately evenly distributed across the at least two cooling channels, the changes in the flow cross-section of the inlet channel or the outlet channel and / or the connecting channels described above typically play a subordinate role for the pressure loss and thus for the volume flow through a respective cooling channel, since the majority of the pressure loss of the fluid occurs when flowing through the cooling channels themselves. This is due to the fact that the cooling channels have a small flow cross-section compared to the connecting channels and the inlet channel or the outlet channel, and the pressure loss generally depends to the fourth power of the flow diameter and linearly on the flow length.Accordingly, despite the change in the flow cross-section of the inlet channel or the outlet channel and / or the distribution channels described above, the volume flow is distributed approximately equally across all cooling channels (provided that they themselves have an identical geometry).

[0047] In a further aspect of the invention, which can be combined in particular with the first or the second aspect, a longitudinal direction of the connecting channels and a longitudinal direction of the inlet channel and / or the outlet channel are aligned with each other at an acute outflow angle, which is preferably less than 70°.

[0048] As described above, there are limitations in the design of the fluid distributor and fluid collector when using conventional manufacturing processes. The connecting channels and the inlet or outlet channel are typically perpendicular to each other in order to redirect the flow into a plane parallel to the cooling channels. This creates sharp edges and limited angular regions where flow separation usually occurs, increasing the FIV excitation or the FIV contribution. To avoid these sharp edges, they can be rounded off or attempts can be made to have the channels run at tangential radii to each other. To reduce flow-induced vibrations, it is easier to reduce the outflow angle between the longitudinal direction of the connecting channels and the longitudinal direction of the inlet or outlet channel.The flatter the outflow angle, the lower the flow-induced vibrations typically are. The acute outflow angle should always be <90° and should be reduced as much as possible, close to the optimum of 0°. In this way, flow separation can be reduced, particularly in the connecting channels. The aspect described here can be advantageously implemented in both the fluid distributor and the fluid collector.

[0049] In a further aspect of the invention, which can be combined in particular with the aspects described above, a distance between the inlet channel and the cooling channels decreases starting from the connecting channel adjacent to the inlet opening and / or a distance between the outlet channel and the cooling channels decreases starting from the cooling channel adjacent to the outlet opening. By aligning the inlet channel or the outlet channel at an angle to the cooling channels, the outflow angle between the longitudinal direction of the connecting channels and the longitudinal direction of the inlet channel or the outlet channel can be reduced. If both the inlet channel or the outlet channel and the connecting channels are aligned at an angle to a surface of the base body under which the cooling channels run, the smallest possible outflow angle can be generated - depending on the dimensions of the base body.In principle, it makes no difference whether the connecting channels alone, the inlet / outlet channels alone, or both simultaneously are inclined toward the surface or the cooling channels to reduce the outflow angle. Further optimization can be achieved by rounding all edges in the direction of flow.

[0050] In one embodiment, the base body has a first partial body and a second partial body, which are rigidly connected to one another along a joining surface, wherein the hollow structure is formed in at least one of the partial bodies. In the event that the component is an optical element in the form of a mirror, in this embodiment the base body (mirror substrate) is typically first produced as a whole, and from this the two or more partial bodies are formed by mechanical processing. Material is removed from at least one of the partial bodies in order to form the hollow structure or part of the hollow structure. The two partial bodies are subsequently rigidly connected to one another along the joining surface. To produce the connection, a bonding process can be used which enables the connection to be produced without the use of a joining agent, for example so-called fusion bonding.The joining surface can be a flat surface, but it is also possible for the joining surface to be a curved surface. The substrate can be a material with the lowest possible coefficient of thermal expansion, for example a glass ceramic, e.g. Zerodur®. The joining of two or more partial bodies to form the base body can be necessary, particularly in the standard manufacturing processes described above, in order to realize complex geometries of the hollow structure. The joining surface typically runs perpendicular or essentially perpendicular to a (vertical) plane in which the connecting channels typically run. This simplifies the manufacture of the hollow structure by drilling, milling and / or grinding in order to realize the designs described above (if necessary approximately).It is understood that the base body may alternatively also be formed in one piece, particularly if the alternative manufacturing processes described above are used.

[0051] If the component is an optical element for reflecting radiation in the form of a mirror, the cooling channels generally run essentially parallel to the reflective surface of the mirror at a comparatively short distance from the reflective surface. At least one section of the fluid distributor and the fluid collector adjacent to the cooling channels is typically oriented essentially perpendicular to the cooling channels, i.e., at an angle between 80° and 100°, in particular at an angle of approximately 90°, in order to remove the fluid from the reflective surface as quickly as possible.

[0052] A further aspect of the invention relates to an optical arrangement, in particular a lithography system, comprising: at least one component designed as described above, in particular an optical element or a structural component, and a cooling device designed for a cooling fluid to flow through the hollow structure of the base body. The lithography system can be a lithography system for exposing a wafer, for example an EUV lithography system that uses radiation at an operating wavelength in the EUV wavelength range. It can also be another optical arrangement for (EUV) lithography, for example an EUV inspection system, e.g. for inspecting masks, wafers or the like used in EUV lithography. The optical element can in particular be a mirror of a projection system of an EUV lithography system.

[0053] The cooling device can, for example, be configured to allow a cooling fluid, typically a cooling liquid, e.g., in the form of cooling water or the like, to flow through the cooling channels. For this purpose, the cooling device can optionally comprise a pump as well as suitable supply and discharge lines. The optical arrangement can also be a lithography system for a different wavelength range, e.g., for the DUV wavelength range, for example, a DUV lithography system or an inspection system for inspecting masks, wafers, optical (mirror) elements, or the like.

[0054] As described above, the component whose base body has the hollow structure does not necessarily have to be an optical element; rather, it can also be a different type of component. The component can, for example, be a structural component, e.g. in the form of a holder, in particular in the form of a frame for holding optical elements, a frame for holding sensors, or in the form of a support frame, as used in EUV lithography systems, especially in EUV lithography devices. In such structural components, the base body is often made of materials such as aluminum, steel, ceramics, e.g. SiSiC, etc. The optical arrangement described above can, in particular, have at least one structural component whose base body has a hollow structure, through which a cooling fluid flows by means of the cooling device.Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details essential to the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0055] drawing

[0056] Examples of embodiments are shown in the schematic drawing and are explained in the following description.

[0057] Fig. 1 shows a meridional section of a projection exposure system for EUV projection lithography,

[0058] Fig. 2 is a schematic representation of a base body of a mirror of the projection exposure apparatus of Fig. 1 with a hollow structure having cooling channels, a fluid collector and a fluid distributor,

[0059] Fig. 3 is a schematic sectional view of the fluid distributor of the hollow structure of Fig. 2 with a representation of the turbulent kinetic energy when a fluid flows through the fluid distributor,

[0060] Fig. 4a is a view analogous to Fig. 3, in which the fluid distributor has an inlet channel with a circular flow cross-section that decreases in the longitudinal direction of the inlet channel,

[0061] Fig. 4b is a representation analogous to Fig. 4a, in which the fluid distributor has conically extending connecting channels, Fig. 5 is a representation of the relationship between the local diameter of the inlet channel and the maximum diameter of the inlet channel with a linear decrease in the flow cross-section in the longitudinal direction of the inlet channel,

[0062] Fig. 6 is a view analogous to Fig. 4a, b with an inlet channel having a rectangular flow cross-section with decreasing height,

[0063] Fig. 7a, b representations of a rectangular flow cross-section and a flow cross-section having a rectangular and a semicircular cross-sectional portion,

[0064] Fig. 8 is a representation analogous to Fig. 6, in which the flow cross-section of the inlet channel decreases in stages,

[0065] Fig. 9a, b a representation analogous to Fig. 3 or to Fig. 7a, b, in which the inlet channel has an annular flow cross-section,

[0066] Fig. 10 is a representation analogous to Fig. 3, in which the inlet channel has a constant flow cross-section and in which a flow cross-section of the connecting channels increases with increasing distance from the inlet opening,

[0067] Fig. 11 is a representation analogous to Fig. 3, in which the inlet channel has a constant flow cross-section and is aligned at an acute outflow angle to the connecting channels, and Fig. 12 is a representation analogous to Fig. 11, in which the inlet channel has a decreasing flow cross-section starting from the inlet opening and in which the connecting channels have an increasing flow cross-section starting from the inlet opening.

[0068] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0069] The following describes, by way of example, the essential components of an optical arrangement for EUV lithography in the form of a projection exposure system 1 for microlithography with reference to Fig. 1. The description of the basic structure of the projection exposure system 1 and its components is not intended to be limiting.

[0070] One 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 provided as a separate module from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] 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.

[0076] 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.

[0077] 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 by way of example in Fig. 1. 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The mirrors Mi, just like the mirrors of the illumination optics 4, can have a highly reflective coating for the illumination radiation 16.

[0082] Fig. 2 shows, by way of example, a base body in the form of a substrate 25 of one of the mirrors Mi of the projection system of Fig. 1. In the example shown, the material of the substrate 25 is Ultra Low Expansion Glass (ULE®). The substrate 25 can also be formed from another material that has the lowest possible thermal expansion coefficient, for example, from a glass ceramic, e.g., Zerodur®.

[0083] A reflective surface in the form of a reflective coating 26 (see Fig. 3) is applied to a surface 25a of the substrate 25. A partial region of the surface 25a, which is located within the reflective coating 26, is struck by the EUV radiation 16 of the projection system 10 and forms an optically used partial region of the reflective coating 26 (not shown). For reflecting the EUV radiation 16, the reflective coating 26 can, for example, have a plurality of layer pairs made of materials, each with a different real part of the refractive index, which can be formed, for example, from Si and Mo at a wavelength of the EUV radiation 16 of 13.5 nm.

[0084] The substrate 25 has a hollow structure 27 through which a fluid 28 can flow, which in the example shown is cooling water. The fluid 28, indicated by an arrow in Fig. 2, enters the substrate 25 via an inlet opening 29 on a side surface to flow through a plurality of cooling channels 31 that form part of the hollow structure 27, thereby cooling, in particular, the surface 25a of the substrate 25 to which the reflective coating 26 is applied.

[0085] To supply the fluid 28 to the inlet opening 29 and to discharge the fluid 28 from an outlet opening 30 of the substrate 25, the projection exposure system 1 has a temperature control device in the form of a cooling device 32, which is illustrated highly schematically in Fig. 1. In the example shown, the cooling device 32 serves to supply the fluid 28 in the form of cooling water to the hollow structure 27 or to the fourth mirror M4 and, for this purpose, has a supply line (not illustrated) that is fluid-tightly connected to the inlet opening 29. The cooling device 32 also has a discharge line (not illustrated) for discharging the cooling water from the substrate 25 or the hollow structure 27 via the outlet opening 30. The other mirrors M1 -M3, M5, M6 of the projection system 10 as well as the mirrors of the illumination system 2 can also be cooled with the cooling device 32 or, if necessary, with further tempering or cooling devices provided for this purpose.Cooling devices can be connected. As can be seen in Fig. 2, the fluid 28 enters a cylindrical inlet channel 33a of the hollow structure 27 via the inlet opening 29, which inlet channel forms part of a fluid distributor 33. A plurality of (first) connecting channels 33b branch off from the inlet channel 33a, each of which is connected to one of the plurality of cooling channels 31. The cooling channels 31 are arranged at a constant distance of less than approximately 10 mm from the surface 25a of the substrate 25, which in the example shown is convexly curved. The surface 25a has a convex curvature along sectional planes XZ, which run perpendicular to the Y direction of an XYZ coordinate system. Along sectional planes YZ, which run perpendicular to the X direction, the surface 25a, however, is flat.The cooling channels 31 run essentially rectilinearly along their longitudinal direction, which corresponds to the X-direction, and extend in the longitudinal direction over approximately the entire partial area of ​​the surface 25a of the substrate 25 covered by the coating 26. The fluid 28 flows from the cooling channels 31 via a plurality of (second) connecting channels 34b to a cylindrical outlet channel 34a of a fluid collector 34. The fluid 28 exits the hollow structure 27 of the substrate 25 via the outlet opening 30 on the end face of the cylindrical outlet channel 34a.

[0086] As can be seen in Fig. 2, the cooling channels 31, starting from the first connecting channels 33b and second connecting channels 34b, initially run in the horizontal direction (X direction), while the (first and second) connecting channels 33b, 34b run in the vertical direction (Z direction). Accordingly, the longitudinal axes of the cooling channels 31 at the transition to a respective connecting channel 33b, 34b are aligned at an angle of 90° to the longitudinal axes of the connecting channels 33b, 34b. Such an alignment at an angle of approximately 90° is typical for the production of the hollow structure 27 in the substrate 25 using a standard processing method, which is described in more detail below. To produce the hollow structure 27, the substrate 25 shown in Fig. 2 is divided into two partial bodies 35a, 35b, which are indicated in Fig. 3. The first, upper part body 35a is essentially plate-shaped.The reflective surface in the form of coating 26 is applied to the first partial body 35a. The second, significantly larger partial body 35b is connected to the first partial body 35a at a common joining surface 36. The two partial bodies 35a, 35b can be connected along the joining surface 36 using a bonding process, for example, fusion bonding. In the example shown, the first partial body 35a and the second partial body 35b are made of the same material (ULE®, see above), but it is also possible for the first partial body 35a and the second partial body 35b to be made of different materials.

[0087] The cooling channels 31 are formed during the manufacture of the hollow structure 27 by removing material from the first partial body 35a, i.e. the cooling channels 31 extend from the joining surface 36 into the first partial body 35a. The fluid distributor 33 and the fluid collector 34 are formed in the second partial body 35b by removing material from the second partial body 35b, i.e. the fluid distributor 33 and the fluid collector 34 extend from the joining surface 36 into the second partial body 35b. In the hollow structure 27 shown in Fig. 2, the material is removed using a standard manufacturing process, more precisely by milling or drilling.

[0088] The illustration in Fig. 3 shows a turbulence field of the liquid 28 flowing through the fluid distributor 33, wherein the contours bordered by dotted and dash-dotted lines represent volume regions with high turbulence and with high turbulent kinetic energy, respectively. As can be seen in Fig. 3, volume regions with high turbulence occur both in the inlet channel 33a, which has a circular flow cross-section, and in the connecting channels 33b, which are also circular-cylindrical. The volume regions with high turbulence lead to flow-induced vibrations. This is due, among other things, to the alignment of the connecting channels 33b and the inlet channel 33a at an angle of 90° to one another, which leads to flow separation, as well as to the different diameters of the connecting channels 33b and the inlet channel 33a. In the embodiment shown in Fig.In the design of the fluid distributor 33 shown in Figure 3, design guidelines for low-turbulence flow guidance are violated due to space limitations.

[0089] It has been shown that the constant flow cross-section of the circular-cylindrical inlet channel 33a is also unfavorable with regard to flow guidance: Due to the fact that the volume flow in the inlet channel 33a decreases starting from the inlet opening 29 because a portion of the volume flow is discharged from the inlet channel 33a through a connecting channel 33b, this leads to a reduction in the flow velocity in the longitudinal direction (y-direction) of the inlet channel 33a. This can lead to flow separation, particularly in the vicinity of the end of the inlet channel 33a facing away from the inlet opening 29, and thus to turbulent and / or periodic fluctuating movements (exponential gradient of the flow velocity), as indicated in Fig. 3.

[0090] The following describes how the velocity or pressure gradient of the fluid 28 in the inlet channel 33a can be homogenized by adjusting the cross-section or by reducing the flow cross-section A of the inlet channel 33a in order to prevent separation of the fluid 28.

[0091] In the example shown in Fig. 4a, b, the inlet channel 33a has a flow cross-section A which, starting from a connecting channel 33b' adjacent to the inlet opening 29, decreases in the longitudinal direction y of the inlet channel 33a. For clarity, Fig. 4a, b show the local, circular flow cross-section A in the region of the connecting channel 33b' adjacent to the inlet opening 29 and at the end of the inlet channel 33a facing away from the inlet opening 29. It is understood that, contrary to the illustration in Fig. 4a, b, the circular flow cross-section A of the inlet channel 33a runs perpendicular to the longitudinal direction y of the inlet channel 33a in the xz plane.

[0092] In the example shown in Fig. 4a, b, the flow cross-section A decreases linearly in the longitudinal direction y of the inlet channel 33a, which has proven to be advantageous for reducing flow-induced vibrations, as this results in a constant decrease in the velocity of the fluid 28 in the axial direction or the pressure gradient. Since the flow cross-section A is proportional to the square of the diameter D 2 or to the radius square R 2 is (A ~ R 2 or D 2), for a linear decrease in the flow cross-section A in the longitudinal direction y of the inlet channel 33a, it is necessary that the diameter D scales with the square root of the distance y from the maximum radius or diameter Do of the inlet channel, as shown in Fig. 5, which shows the ratio D(y) / Do as a function of the y-coordinate, where the numerical values ​​on the abscissa of the graph shown in Fig. 5 correspond to the twelve positions in the longitudinal direction (y-direction) of the inlet channel 33a shown in Fig. 4a. The curve shown in Fig. 5 can be analytically described by the following equation: D(y) / Do = 0.2887 xy 05 .

[0093] Unlike what is shown in Fig. 4a, b, the profile shown in Fig. 5 can, if necessary, be approximated by inserting linearly approximated sections between the twelve positions shown in Fig. 4a, i.e., two of the numerical values ​​shown in Fig. 5 are connected by a straight line. Such an approximated linear profile can be advantageous from a manufacturing technology perspective. In Fig. 4a, the turbulent kinetic energy of the fluid 28 in the fluid distributor 33 is shown, analogous to the representation in Fig. 3. A comparison between Fig. 4a and Fig. 3 shows that the turbulent kinetic energy in the inlet channel 33a of Fig. 4a is significantly reduced compared to the inlet channel 33a of Fig. 3. If this effect is quantified with regard to the impact on flow-induced vibrations, it turns out that a reduction of approximately 30-90% is possible.A further reduction of the flow-induced vibrations can be achieved by further iterative optimization of the profile of the flow cross-section A in the longitudinal direction y of the inlet channel 33a.

[0094] As can also be seen in Fig. 4a, the flow cross-section A of the inlet channel 33a decreases with increasing distance from the inlet opening 29, while the diameter or flow cross-section of the connecting channels 33b remains constant in the longitudinal direction y of the inlet channel 33a. This leads to a significant cross-sectional jump occurring near the left end of the inlet channel 33a in Fig. 4a at the transition to the respective connecting channels 33b. In order to counteract a local increase in the flow-induced vibrations due to the cross-sectional jump, in the example shown in Fig. 4b, an opening cross-section M of a respective connecting channel 33b decreases starting from the connecting channel 33b' adjacent to the inlet opening 29. The connecting channels 33b have an (averaged) flow cross-section Av that decreases with increasing distance from the cooling channels 31.

[0095] In the example shown in Fig. 4b, the connecting channels 33b are conical and each have an opening angle δ of less than 8°. The opening cross-section AM of each connecting channel 33b was selected such that, as far as possible, no cross-sectional jump occurs at the transition between the inlet channel 33a and the respective connecting channel 33b, i.e., the opening cross-section AM is determined by the local diameter D(y) of the inlet channel 33a.

[0096] Fig. 6 shows a further possibility for generating a linear decrease in the flow cross-section A in the longitudinal direction y of the inlet channel 33a. In the example shown in Fig. 6, the flow cross-section A is rectangular and has a height h extending in the vertical direction (z-direction) and a width b extending transversely to the plane (yz-plane) in which the connecting channels 33b and the inlet channel 33a lie (see also Fig. 7a). As indicated in Fig. 6, the width b of the rectangular flow cross-section A in the longitudinal direction y of the inlet channel 33a is constant, but the height h of the rectangular flow cross-section A decreases linearly starting from the connecting channel 33b' adjacent to the inlet opening 29. Accordingly, the flow cross-section A in the longitudinal direction y of the inlet channel 33a also decreases linearly, since this is proportional to the height h (A ~ h).The relationship between the height h(y) and the y-coordinate in the longitudinal direction y of the inlet channel 33a, whose zero point was (arbitrarily) set at the end of the inlet channel 33a facing away from the inlet opening 29, results in the example shown in Fig. 6 as: h(y) = ho + y / L (h. E - ho), where ho is the minimum height, h Edenotes the maximum height and L the length of the inlet channel 33a, along which the flow cross-section A decreases linearly. Due to the constant width b of the flow cross-section A, the problem of a cross-sectional jump at the transition between the inlet channel 33a and the connecting channels 33b, as described in connection with Fig. 4a, b, is eliminated. In the example shown in Fig. 6, the connecting channels 33b therefore have a constant, circular flow cross-section Av, as indicated in Fig. 6. It is understood that the inlet channel 33a does not have to have a decreasing flow cross-section A over its entire length; rather, the flow cross-section can be constant, for example, in the section of the inlet channel 33a which is arranged adjacent to the inlet opening 29 and in which no connecting channels 33b open into the inlet channel 33a. This can be advantageous, for example, in order to connect the inlet channel 33a to a fluid connection.

[0097] Instead of the rectangular flow cross-section A shown in Fig. 7a, the inlet channel 33a can have a flow cross-section A shown in Fig. 7b, which is composed of a rectangular cross-sectional area AR and a semicircular cross-sectional area AK. Also, in the flow cross-section A shown in Fig. 7b, the width b of the rectangular cross-sectional area AR is constant, and its height h decreases linearly in the longitudinal direction y of the inlet channel 33a. It is understood that the inlet channel 33 can also have flow cross-sections A with geometries other than those shown in Fig. 4a, b and Fig. 7a, b.

[0098] It is not absolutely necessary for the flow cross-section A of the inlet channel 33a to decrease continuously (linearly). Rather, it is also possible for the flow cross-section A to decrease in steps or in stages (cascaded), as shown in Fig. 8 for the rectangular flow cross-section A shown in Fig. 6. The greater the number of stages, the smaller the change in the flow cross-section A at each stage is as a rule. Excessive changes in the flow cross-section (> 5% relative to the larger flow cross-section at the stage) should be avoided in order to prevent local flow separation. In Fig. 8, the flow cross-section A is reduced in comparatively large steps for illustrative purposes. As an alternative to the rectangular flow cross-section A shown in Fig. 8, the gradually decreasing flow cross-section A can have a different geometry.The stepped reduction in the flow cross-section A enables the manufacture of the inlet channel 33a using conventional manufacturing processes, albeit with increased complexity. In general, the designs of the fluid distributor 33 described above are typically manufactured using alternative or novel manufacturing processes, for example, selective laser etching or backside laser ablation.

[0099] In the mirror Mi shown in Fig. 9a, the inlet channel 33a has an annular flow cross-section A, which is illustrated in Fig. 9b. To create the annular flow cross-section A, material is removed from the base body 25 of the mirror Mi in the form of a ring, forming a truncated cone 37 with a circular cross-sectional area, the radius r of which increases with increasing distance from the inlet opening 29, as can be seen in Fig. 9a. The outer radius R or the outer diameter D of the annular flow cross-section A of the inlet channel 33a formed in this way is constant. In this way, a circular annular gap is created with a decreasing flow cross-section A starting from the inlet opening 29 or from the connecting channel 33b' adjacent to the inlet opening 29. For the annular flow cross-section A, the following applies in the example shown in Fig. 9a, b:

[0100] A = IT (R 2 - r 2) = IT (d + b) b = IT (D - b) b, where b and thus also the flow cross-section A depend on the y-coordinate or the longitudinal direction of the inlet channel 33a. Also in the case shown in Fig.

[0101] In the example shown in Fig. 9a, b, a linear decrease of the flow cross-section A in the longitudinal direction of the inlet channel 33a can occur if the width b(y) is chosen appropriately.

[0102] It is understood that the annular flow cross-section A does not necessarily have to be circular, but can have a different geometry, e.g., elliptical, rectangular, oval, or a free-form geometry. As an alternative to the example shown in Fig. 9a, b, the truncated cone 37 may not be part of the base body 25, but rather an additional component that is introduced into the inlet channel 33a, which in this case is cylindrical, via the inlet opening 29 and suitably fixed. The additional component, which in this case is rod-shaped, can, for example, be attached to a fluid line that is attached to the inlet opening 29 and fixed there.

[0103] Fig. 10 shows a mirror Mi in which, in contrast to the examples described above, the inlet channel 33a has a constant flow cross-section A. In the example shown in Fig. 10, the connecting channels 33b have different flow cross-sections Av. The different flow cross-section Av of the connecting channels 33b can influence the back pressure or the volume flow discharge from the inlet channel 33a in order to generate a pressure gradient in the inlet channel 33a that is as constant as possible. To achieve this, the flow cross-section Av of each connecting channel 33b can be individually determined. It has been shown that, in order to reduce flow-induced vibrations, it is advantageous if the flow cross-section Av of the connecting channels 33b increases starting from the connecting channel 33b adjacent to the inlet opening 29.

[0104] In the example shown in Fig. 10, this is achieved by providing three groups G1, G2, G3 of connecting channels 33b, each having the same flow cross-section Av. The flow cross-section Av of the third group G3, which is arranged adjacent to the inlet opening 29, is smaller than the flow cross-section Av of the second group G2, and the flow cross-section Av of the second group G2 is smaller than the flow cross-section Av of the first group G1 of connecting channels 33b.

[0105] Also visible in Fig. 10 is the turbulent kinetic energy within the fluid distributor 33, which is significantly reduced (approximately by 10% - 50%) compared to the conventional fluid distributor 33 shown in Fig. 3. The example shown in Fig. 10 can serve as a starting point for an iterative optimization of the flow guidance in the fluid distributor 33, in which the flow cross-section Av in the respective connecting channels 33b is individually determined. It is understood that a different division of the connecting channels 33b into groups is also possible; for example, four groups can be formed, each with three connecting channels 33b, each having the same flow cross-section Av.

[0106] As can also be seen in Fig. 10, the connecting channels 33b of the second and third groups G2, G3 each have a conical section 38 at the transition to the cooling channels 31. The conical section 38 serves to prevent a cross-sectional jump at the transition between the respective connecting channel 33b and the cooling channels 31. As can be seen in Fig. 10, each of the connecting channels 33b is connected to two adjacent cooling channels 31, to which the fluid 28 is supplied. By means of the conical section 38 of the connecting channels 33b of the second and third groups G2, G3, which have a flow cross-section Av that is smaller than the distance in the y-direction between two adjacent cooling channels 31, a cross-sectional jump at the transition to the cooling channels 31 can be avoided. It is understood that with regard to the arrangement and design of the conical sections 38, it is possible to deviate from the configuration shown in Fig. 10.In the examples described above, the connecting channels 33b are aligned in the vertical direction (z-direction) and the inlet channel 33a runs in the horizontal direction (y-direction), resulting in a 90° deflection of the fluid 28 at the mouth of the connecting channels 33b, which can cause flow separation, resulting in flow-induced vibrations. To reduce the flow-induced vibrations, an acute outflow angle is used in the example shown in Fig. 11. <p zwischen einer Längsrichtung Lv der Verbindungskanäle 33b und einer Längsrichtung LE des Einlasskanals 33a gewählt, der bei weniger als ca. 70° liegt. Um einen möglichst kleinen Abströmwinkel <p zu erzeugen, ist bei dem in Fig. 11 gezeigten Beispiel ein jeweiliger Verbindungskanal 33b unter einem Winkel zur z-Richtung ausgerichtet und auch der Einlasskanal 33a ist unter einem Winkel a zu einer horizontalen Ebene (xy-Ebene) ausgerichtet. Entsprechend nimmt bei dem in Fig.In the example shown in Fig. 11, a distance Dz in the z-direction between the cooling channels 31 and the inlet channel 33a, starting from the connecting channel 33b' adjacent to the inlet opening 29, is determined. Unlike what is shown in Fig. 11, for the generation of an acute outflow angle <p ausreichend, wenn die Längsrichtung LE des Einlasskanals 33a gegenüber der Horizontalen geneigt ist oder wenn die Längsrichtung Lv der Verbindungskanäle 33b gegen die z-Richtung geneigt ist.

[0107] Fig. 12 shows a mirror Mi in which the three measures described above, i.e. the reduction in the flow cross-section A in the inlet channel 33a, as described in connection with Fig. 4a, b Fig. 6 and Fig. 8, the increase in the flow cross-section Av in the connecting channels 33b, as described in connection with Fig. 10, and the use of an acute outflow angle αp, as described in connection with Fig. 11, are combined with one another. In the design of the fluid distributor 33 shown in Fig. 12, attention must be paid to any interaction between the individual measures that may occur. In the hollow structure 27 described above, it was assumed that the fluid distributor 33 and the fluid collector 34 have an identical geometry, i.e. that what was said above with regard to the fluid distributor 33 also applies analogously to the fluid collector 34.However, it is fundamentally possible for the fluid distributor 33 and the fluid collector 34 to have a different geometry, since a different dimensioning for the fluid collector 34 may be more advantageous than the dimensioning of the fluid distributor 33.

[0108] The component whose base body 25 has the hollow structure 27 does not necessarily have to be an optical element in the form of a mirror Mi. It can also be another optical element or a non-optical component, for example, a structural component of the projection exposure system 1. The component having the base body 25 with the flow-optimized hollow structure 27 can also be used in an optical arrangement other than the projection exposure system 1 described above, for example, in a lithography system designed for the DUV / VUV wavelength range.

[0109] In general, flow guidance can also be improved by rounding sharp edges, etc., of the hollow structure 27, thereby reducing flow-induced vibrations. The introduction of radii instead of sharp, angular transitions within the hollow structure 27 also has a beneficial effect on reducing flow-induced vibrations.

Claims

Patent claims 1 . Component, in particular optical element (Mi) or structural component, comprising: a base body (25) which has a hollow structure (27) through which a fluid (28) can flow, which has a plurality of cooling channels (31), a fluid distributor (33) and a fluid collector (34), wherein the fluid distributor (33) is designed to supply the fluid (28) to the cooling channels (31) has connecting channels (33b) which open into a common inlet channel (33a) which is connected to an inlet opening (29), and / or in which the fluid collector (34) for discharging the fluid (28) from the cooling channels (31) has connecting channels (34b) which open into a common outlet channel (34a) which is connected to an outlet opening (30), characterized in that the inlet channel (33a) has a flow cross-section (A) which decreases starting from a connecting channel (33b') adjacent to the inlet opening (29), and / or that the outlet channel (34a) has a flow cross-section which decreases starting from a connecting channel adjacent to the outlet opening (30).

2. Component according to claim 1, in which the flow cross-section (A) of the inlet channel (33a) decreases linearly in the longitudinal direction (y) and / or in which the flow cross-section of the outlet channel (34a) decreases linearly in the longitudinal direction (y).

3. Component according to claim 1 or 2, wherein the inlet channel (33a) and / or the outlet channel (34a) have a flow cross-section (A) which is circular.

4. Component according to claim 1 or 2, wherein the inlet channel (33a) and / or the outlet channel (34a) have a rectangular flow cross-section (A) or a rectangular cross-sectional partial area (AR), wherein preferably a width (b) of the rectangular flow cross-section (A) or of the rectangular cross-sectional partial area (AR) is constant and a height (h) of the rectangular flow cross-section (A) or of the rectangular cross-sectional partial area (AR) decreases, in particular decreases linearly.

5. Component according to claim 4, wherein the inlet channel (33a) and / or the outlet channel (34a) have a flow cross-section (A) which is composed of the rectangular cross-sectional area (AR) and a semicircular cross-sectional area (AK).

6. Component according to one of claims 1 or 2, wherein the inlet channel (33a) and / or the outlet channel (34a) have a flow cross-section (A) which is annular.

7. Component according to one of the preceding claims, in which an opening cross-section (AM) of a respective connecting channel (33b) of the fluid distributor (33) decreases starting from the connecting channel (33b') adjacent to the inlet opening (29) and / or in which an opening cross-section (AM) of a respective connecting channel (34b) of the fluid collector (34) decreases starting from the connecting channel (33b) adjacent to the outlet opening (30).

8. Component according to one of the preceding claims, in which at least one connecting channel (33b, 34b) has a flow cross-section (Av) which decreases with increasing distance from the cooling channels (31).

9. Component according to claim 8, wherein the at least one connecting channel (33b, 34b) is conical, wherein an opening angle (θ) of the at least one conical connecting channel (33b, 34b) is preferably less than 8°.

10. Component according to one of the preceding claims, in which the flow cross-section (A) of the inlet channel (33a) and / or the outlet channel (34a) decreases in stages.

11. Component according to the preamble of claim 1, wherein the inlet channel (33a) has a constant flow cross-section (A) and / or wherein the outlet channel (34a) has a constant flow cross-section (A), and wherein at least two of the connecting channels (33b, 34b) each have a different flow cross-section (Av).

12. Component according to one of the preceding claims, in which a flow cross-section (Av) of the connecting channels (33b, 34b) increases starting from a connecting channel (33b') adjacent to the inlet opening (29) or starting from a connecting channel (34b') adjacent to the outlet opening (30).

13. Component according to one of the preceding claims, in which the flow cross-section (Av) of at least two, preferably of at least three adjacent connecting channels (33b, 34b) is of the same size.

14. Component according to one of the preceding claims, in which at least one connecting channel (33b) has a conical section (38) at the transition to the cooling channels (31).

15. Component according to the preamble of claim 1, in particular according to one of the preceding claims, in which a longitudinal direction (Lv) of the connecting channels (33b) and a longitudinal direction (LE) of the inlet channel (33a) and / or the outlet channel (34a) are aligned with one another at an acute outflow angle (cp), which is preferably less than 70°.

16. Component according to the preamble of claim 1, in particular according to one of the preceding claims, in which a distance (D z ) between the inlet channel (33a) and the cooling channels (31) decreases starting from the connecting channel (33b') adjacent to the inlet opening (29) and / or in which a distance between the outlet channel (34a) and the cooling channels (31) decreases starting from the cooling channel (34b') adjacent to the outlet opening (30).

17. Component according to one of the preceding claims, in which the base body (25) has a first partial body (35a) and a second partial body (35b) which are rigidly connected to one another along a joining surface (36), wherein the hollow structure (27) is formed in at least one of the partial bodies (35a, 35b).

18. Optical arrangement, in particular lithography system (1), comprising: at least one component according to one of the preceding claims, in particular an optical element (Mi) or a structural component, and a cooling device (32) which is designed for a cooling fluid (28) to flow through the hollow structure (27) of the base body (25).

Images