Fluid supply device and method for supplying a fluid to at least one ablation front

Abstract

Fluid supply device (38) for supplying a fluid (28) to at least one ablation front (30a, 30b) when removing material from a workpiece by multi-photon laser ablation, comprising: a plurality of flexible fluid lines (41) for supplying the fluid (28) to the at least one ablation front (30a, 30b), and at least one insert component (39, 40) for insertion into a cavity (33, 35) of the workpiece (25), wherein the insert component (39, 40) has a plurality of guide channels (47), in each of which a flexible fluid line (41) is guided in order to supply the fluid (28) to the at least one ablation front (30a, 30b).

Description

Background of the invention

[0001] The invention relates to a fluid supply device for supplying a fluid to at least one ablation front during the removal of material by multi-photon laser ablation from a workpiece, preferably from a particularly monolithic substrate for an EUV mirror. The invention also relates to a method for supplying a fluid to the at least one ablation front during the removal of material by multi-photon laser ablation from a workpiece, preferably from a particularly monolithic substrate for an EUV mirror, using such a fluid supply device.

[0002] In EUV lithography, projection exposure systems are used to manufacture semiconductor components. These systems operate with short-wavelength radiation, so-called EUV radiation, at an operating wavelength between approximately 5 nm and approximately 30 nm. Due to the short-wavelength radiation, coated mirrors (EUV mirrors) are used for beam guidance and focusing. These mirrors have a substrate made of a material with a very low coefficient of thermal expansion. The substrate material can, for example, be titanium-doped quartz glass, known under the trade name "Ultra-Low-Expansion" (ULE®) glass. The substrate material can also be certain glass-ceramics that have a low coefficient of thermal expansion and are sold, for example, under the trade names "Clearceram®" or "Zerodur®".Productivity during the production of exposed wafers depends heavily on the power of the EUV light source used to generate the EUV radiation. However, high radiation power impinging on the EUV mirrors leads to increased thermal stress on the EUV mirrors. Despite the extremely low coefficient of thermal expansion, the heat introduced into the substrate leads to increasingly intolerable shape deviations of the high-precision mirror surfaces. To meet the demand for growing productivity and the resulting ever more powerful EUV light sources, active cooling of the EUV mirrors is therefore necessary.

[0003] Due to the fact that typical substrate materials have very low thermal conductivity and material thicknesses on the order of several centimeters, it is necessary to dissipate the generated heat over a large area. The most efficient method is volumetric cooling in the form of internal cooling channels through which a liquid, e.g., water, flows. A crucial challenge here is the realization of hollow structures in the form of cooling channels within the volume of the substrate. These hollow structures have a comparatively large cross-section, usually more than approximately 1 mm, and run a short distance below the optical surface of the substrate, to which a reflective coating is applied to reflect EUV radiation.

[0004] Substrate materials for EUV mirrors, e.g., titanium-doped quartz glass (ULE®), are successively built up from SiO2 and TiO2 by flame hydrolysis, among other processes. The creation of hollow structures in the form of cooling channels can therefore only be carried out subsequently in the volume of the workpiece material. Conventionally, hollow structures in hard and brittle materials such as glass or (glass) ceramics can be realized by mechanical processing, e.g., by drilling (e.g., using a diamond drill bit) or ultrasound-based ablation. Both the structural diversity and the achievable depth of the hollow structures produced in this way are severely limited. Furthermore, there is a risk of significant stress and damage to the material, particularly with tactile processes.

[0005] DE102015210286A1 and WO2016192938A1 describe a method and an associated device in which workpiece material is ablated within a respective focal region within a workpiece, e.g., a plane-parallel plate. During processing, the back of the workpiece is brought into contact with a flowable liquid that is transparent to the laser radiation, at least in a processing area encompassing the focal region. For this purpose, a nozzle connected to a liquid line can be used to transport the ablation products away and to cool the workpiece. The liquid can be directed to the back of the workpiece in the form of a free liquid jet using a trackable nozzle, or the workpiece can be (partially) immersed in a liquid bath.

[0006] WO2016192938A1 describes how this method can be used to create cylindrical through-holes with a diameter of approximately 500 µm in glass with a thickness in the range of millimeters. The method involves moving the laser beam in a processing plane parallel to the workpiece surface using a scanner with a predefined movement pattern. To create the through-hole, the processing plane is shifted several times in the thickness direction of the workpiece, and the scanning process is repeated several times with a predefined movement pattern. The creation of straight, cylindrical holes in transparent materials such as glass or sapphire is also described in the article "FSLA - Laser Processing of Glass and Sapphire," Liebers, R. and Gebhardt, M., Laser Technik Journal, 14: 23-25 ​​(2017).

[0007] DE 10 2018 202 687 A1 describes a method for producing a cavity structure of a component in a projection exposure system by selective laser etching.

[0008] DE 10 2016 221 878 A1 describes a method for producing a component of a projection exposure system for semiconductor lithography, in which selective laser etching is used.

[0009] FR2531868A1 discloses a device for treating a wound, comprising an inner tube and an outer tube. The inner tube leads via a Y-piece to a dropper bottle for irrigating fluid, while the outer tube is connected to a suction bottle. The device combines a draining function with a rinsing function.

[0010] The method described in DE102015210286A1 and WO2016192938A1 enables the low-damage and low-stress production of hollow structures in the form of straight through-holes in a workpiece. However, many applications require the production of hollow structures with a more complex geometry than a straight, cylindrical through-hole. This is the case, for example, with the substrates for mirrors for EUV lithography described above, into which hollow structures in the form of channels are to be introduced, which are generally not straight.

[0011] Even when manufacturing complex hollow structures, which may, for example, have branches, it is necessary to bring the ablation front or the processing area into contact with a fluid in order to transport the ablation products away, to cool the workpiece locally and to avoid thermal stresses that can lead to damage to the material and the occurrence of stress birefringence. Object of the invention

[0012] The object of the invention is to provide a fluid supply device and a method which make it possible to supply a fluid to at least one ablation front even when producing complex hollow structures. Subject of the invention

[0013] This object is achieved by a fluid supply device of the type mentioned at the outset, comprising: a plurality of flexible fluid lines for supplying the fluid to the at least one ablation front, preferably to a plurality of ablation fronts, and an insert component for insertion into a cavity of the workpiece, wherein the insert component has a plurality of guide channels, in each of which a flexible fluid line is guided in order to supply the fluid to the at least one ablation front.

[0014] The fluid supply device according to the invention comprises a plurality of flexible fluid lines for supplying the fluid to the (at least one) ablation front, which is moved during the production of a hollow structure in the material of the workpiece. These lines can be guided along the ablation front as it moves through the workpiece. In order to position the respective flexible fluid line, more precisely its free end at which the fluid exits, at a predetermined location within the substrate, the respective flexible fluid line in the fluid supply device according to the invention is guided in a guide channel of an insert component, which is inserted into a cavity in the workpiece.

[0015] This is particularly advantageous if one or more structures branch off from a wall of the cavity, which are formed by multi-photon laser ablation, since in this case the respective end of the fluid line can be positioned with the aid of the insert component or the guide channel at a point on the wall of the cavity from which the structure originates, and can be guided along the ablation front when the structure is formed.

[0016] It is possible that a short section of the structure branching off from the cavity is already produced by multi-photon laser ablation before the insert component is inserted into the cavity. In order to supply a fluid to the ablation front formed in this process, the workpiece can be at least partially immersed in a liquid bath. As soon as the ablation front is at a distance of typically more than approximately 20-40 mm from the wall of the cavity, immersion in the liquid bath is generally no longer sufficient, as the ablated material can no longer be sufficiently transported away and the ablation process comes to a standstill. For the production of structures that branch off from the cavity and have a length greater than approximately 20-40 mm, it is necessary to feed the fluid with the aid of a flexible fluid line as the ablation front moves.

[0017] A flexible fluid line can also be guided along the ablation front without an insert component, provided the hollow structure created by the multi-photon ablation does not branch or otherwise have an overly complex geometry. As described above, however, the insert component can be used to position the flexible fluid line at the point where a structure is to originate or branch off from the cavity. Therefore, even with a hollow structure that has branches, the insert component can ensure the supply of fluid to the ablation front without requiring manual threading of the flexible fluid line(s) into the structure(s) branching off from the cavity.

[0018] In multi-photon laser ablation, to form a hollow structure, pulsed laser radiation, typically ultrashort pulse laser radiation, is irradiated through the substrate material to a location on the back of the workpiece or on a surface within the workpiece, for example, on a wall of the cavity described above, from which the structure to be formed is to originate. In multi-photon laser ablation, an ablation front is generated, which, starting from this location, is moved through the substrate material to form the hollow structure. For details on the removal of material by multi-photon laser ablation, reference is made to WO2016192938A1, which is incorporated by reference in its entirety into this application.

[0019] For the production of hollow structures with complex geometries, the method described in WO2016192938A1 can be modified by aligning the ablation front or processing plane not perpendicular to the direction of incidence of the pulsed laser radiation, which typically runs along a thickness direction of the workpiece, but tilting it relative to a plane perpendicular to the direction of incidence, as described below. In this way, non-rectilinear hollow structures with undercuts can also be produced using multi-photon laser ablation.

[0020] The fluid is typically a liquid, such as water, which exits the flexible fluid line at a relatively high pressure, usually several bar. Instead of a liquid, a gas, such as compressed air, can also be brought into contact with the ablation front to transport the ablation products away. A nozzle for the fluid to exit can be attached to the free end of the flexible fluid line (or hose), but this is not mandatory.

[0021] The workpiece is preferably a monolithic substrate, in particular for an EUV mirror. A monolithic substrate is formed in one piece and has no joining surface at which two or more partial bodies of the substrate are connected to one another. As described above, hollow structures in such a monolithic substrate cannot be easily produced by mechanical processing, e.g. by drilling or grinding, in the hard and brittle glass material, which can be, for example, titanium-doped quartz glass or a glass ceramic. The cavity described above can be produced by mechanical processing; for example, the cavity can be a hole that is milled into the substrate.In principle, it is also possible for the cavity to be created by multi-photon laser ablation, although this process is time-consuming when producing cavities with large diameters.

[0022] In the fluid supply device according to the invention, the insert component has a plurality of guide channels, in each of which a flexible fluid line is guided. As described above, the production of hollow structures by multi-photon laser ablation is comparatively slow: each ablation front typically moves at a speed of a few millimeters per hour. In the case of a hollow structure which may have a considerable number of channels or other structures emanating from the cavity, it is therefore advantageous to produce the multiple channels or other structures simultaneously. For this purpose, several pulsed laser beams can be irradiated through the volume of the workpiece at the same time in order to simultaneously form several ablation fronts at which the material of the workpiece is ablated, whereby several structures or other structures branching off from the cavitychannels can be created simultaneously.

[0023] The simultaneous creation of multiple removal fronts requires the simultaneous supply of fluid to the removal fronts using a corresponding number of guide channels or flexible fluid lines that track the respective removal fronts. Ideally, all structures branching off from the cavity can be produced in parallel. If the number of branching structures is too large, they can be divided into several groups, each of which is machined together in parallel. Differently designed insert components can be used to produce each group of structures.

[0024] In a further embodiment, a flow-through gap, in particular an annular gap, is formed between the fluid line and a channel wall of the guide channel for returning the fluid from the ablation front. The flexible fluid line has a diameter selected such that the fluid supplied to the ablation front in the fluid line can be discharged again via the flow-through gap. The flow cross-section of the gap should generally correspond at least to the flow cross-section of the fluid in the flexible fluid line.

[0025] In a further embodiment, the guide channel has at least one rounded section for changing the direction of the flexible fluid line. As a rule, the structures branching off from the cavity in the workpiece do not run parallel to the direction along which the insert component is inserted or introduced into the workpiece. If the respective guide channel starts from the end face of the insert component, it is therefore usually necessary to change the direction of the flexible fluid line within the insert component. Such a change in direction is ideally achieved by guiding the fluid line along a rounded or curved section of the guide channel. At the rounded section, the direction of the flexible fluid line preferably changes at an obtuse angle, i.e. at an angle greater than 90°.

[0026] In a further embodiment, the insert component is rod-shaped and the (at least one) guide channel extends from an end face of the insert component to a lateral surface of the insert component. In this case, the cavity in the workpiece is typically a rectilinear channel, preferably having a constant diameter, which extends from an opening on one side of the workpiece into the volume of the workpiece. In this case, the insert component is inserted into the cavity by being pushed through the opening in the workpiece. The end face of the insert component is accessible from the outside through the opening in the workpiece, so that the flexible fluid lines on the end face of the insert component can be guided away from the workpiece and connected to a device for providing the fluid, which has a pump or the like.With the help of the rounded section of the guide channel described above, a respective flexible fluid line can be guided from the front side of the insert component to the outer surface of the insert component.

[0027] In a further development of this embodiment, the guide channels on the shell side of the insert component open into openings, which are preferably arranged next to one another in the longitudinal direction of the insert component and which are in particular arranged at equal distances from one another in the longitudinal direction of the insert component. An arrangement of the openings next to one another in the longitudinal direction of the insert component is understood to mean that the openings run along a common straight line or line that extends in the longitudinal direction of the insert component. In other words, the openings are not offset from one another in the circumferential direction of the insert component. This is advantageous if a plurality of structures that branch off from the cavity along a common line are to be produced by multi-photon laser ablation. If the structures to be formed are arranged at equal distances from one another, the openings are also equidistant in the longitudinal direction of the insert component, i.e.arranged at equal distances from each other.

[0028] In a further development of this embodiment, the rod-shaped insert component is (circular) cylindrical and preferably has a diameter of between 5 mm and 10 mm. The geometry of the insert component is adapted to the geometry of the cavity, which in this case is also (circular) cylindrical. The diameter of the cavity is slightly larger than the diameter of the insert component. A cylindrical cavity which has a comparatively large diameter can be produced by mechanical processing, e.g. by grinding, and can be designed, for example, as a (blind) bore. In this case, the insert component is typically pushed into the cylindrical cavity until it rests against the end face of the cavity. In this way, the position of the openings in the longitudinal direction of the insert component is determined. The insert component is additionally aligned orrotated so that the openings in the outer surface of the insert component are positioned circumferentially so that they correspond to the points from which the structures branching off from the cavity are to originate. Furthermore, the end face of the insert component can have a protruding section (tongue) that engages with a notch or groove in the workpiece to facilitate axial positioning (lock and key principle). Before inserting the insert component, it is possible to insert a spacer, e.g. in the form of a solid cylinder, into the cavity, with the end face of which the insert component is brought into contact. In this way, the length of the insert component can be reduced.

[0029] In a further embodiment, the at least one guide channel has an (inner) diameter between 1 mm and 4 mm. The structures extending from the cavity generally have a significantly smaller diameter than the insert component. This is advantageous because it allows the insert component to accommodate several guide channels that run within the insert component.

[0030] In a further embodiment, the at least one fluid line has an outer diameter of 1 mm or less. As described above, it is generally necessary to maintain a gap between the fluid line and the wall of a respective guide channel for the return of the fluid. The outer diameter of the fluid line is therefore correspondingly smaller than the (inner) diameter of the guide channel.

[0031] The insert component can be designed in different ways. For example, the guide channels can be designed as tubes, such as stainless steel or plastic tubes, which are bent to form the rounded section(s). The guide channels in the form of tubes, such as stainless steel or plastic tubes, can be bundled and cast in a suitable material, for example, to produce an insert component with a desired geometry, such as a cylinder.

[0032] Alternatively, the insert component can be manufactured using an additive manufacturing process. In this case, the insert component typically consists of a body produced using a 3D printing process, in which the guide channels are formed as hollow structures during additive manufacturing. Metals, plastics, or even glass-like materials typical for 3D printing can be used to produce the insert component.

[0033] In a further embodiment, the fluid supply device comprises a fluid supply device for supplying the fluid to the at least one flexible fluid line. The fluid supply device can have a fluid reservoir for supplying the fluid. As described above, it is typically advantageous to allow the fluid to exit the fluid line at a comparatively high pressure of several bar. It is therefore advantageous to supply the fluid to the flexible fluid line with the aid of a pump that generates a correspondingly high pressure and is part of the fluid supply device.

[0034] In a further embodiment, the fluid supply device comprises at least one tracking device for the automated tracking of the at least one flexible fluid line during movement of the ablation front in the material of the workpiece. In multi-photon laser ablation, the ablation front typically moves at a constant processing speed within the volume of the workpiece. The automated tracking of the flexible fluid line also occurs at the processing speed. For tracking, the flexible fluid line is pushed forward, for example, by being unwound from a spool or the like at a constant speed. For tracking of the flexible fluid line, it is necessary that the material of the fluid line has sufficient shear stiffness, which is typically the case with the materials used for flexible fluid lines.In the event that the ablation fronts move at different processing speeds in the material of the workpiece, the tracking device can be designed to track the fluid lines at an individually adapted speed.

[0035] A further aspect of the invention relates to a method for supplying a fluid to at least one ablation front during the removal of material from a workpiece by multi-photon laser ablation, preferably from a particularly monolithic substrate for an EUV mirror, by means of a fluid supply device designed as described above, wherein the method comprises: inserting the insert component into a cavity of the workpiece, and supplying the fluid to the at least one ablation front through the at least one flexible fluid line guided in the at least one guide channel of the insert component. As described above, with the aid of a fluid supply device designed as described above, the flexible fluid line can be automatically guided along the ablation front as it moves through the workpiece.

[0036] In one variant, the cavity is filled with a fluid before the insert component is inserted, and starting from the fluid-filled cavity, a plurality of channel sections adjacent to the cavity are formed by multi-photon laser ablation. For the production of comparatively short sections of channels or other structures that originate from or branch off from the cavity, local supply of a fluid to the ablation front using a (flexible) fluid line is typically not required: With a channel section length that is usually no more than approximately 20-40 mm, it is sufficient if the cavity as a whole—and thus also the channel sections formed during multi-photon absorption—is filled with a fluid. Typically, for this purpose, the workpiece is partially immersed in a liquid or liquid bath, usually a water bath, with the fluid.

[0037] In a further development of this variant, after the insertion of the insert component into the cavity, a plurality of ablation fronts are generated starting from the end faces of the channel sections and moved in the material of the workpiece in order to generate a plurality of channels, wherein the majority of the flexible fluid lines are guided during the movement of the ablation fronts in the material of the workpiece.

[0038] In the event that the workpiece is a substrate for an EUV mirror, it can, for example, have two cavities, one serving as a fluid distributor and the other as a fluid collector, into each of which an insert component is placed. The two cavities are fluidically connected to one another by a plurality of channels that branch off from the first cavity and open into the second cavity. Starting from one of the two cavities, a first or second channel section, corresponding to approximately half the length of each channel, can be produced by multi-photon laser ablation. Approximately in the middle of the channel's length, the ablation fronts of the two channel sections overlap during production, creating a continuous channel that connects the fluid distributor to the fluid collector.

[0039] In the case of cooling channels or cooling structures for an EUV mirror, they typically do not run in a straight line between the fluid distributor and the fluid collector, but are angled and usually have a distribution channel in which the fluid is transported from the fluid distributor, which is a comparatively large distance from the optical surface of the EUV mirror, to the vicinity of the surface. In a channel section that forms a cooling channel, the fluid, typically in the form of cooling water, is guided along the surface before being guided away from the surface in a collector channel and fed to the fluid collector.

[0040] 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. drawing

[0041] Examples of embodiments are shown in the schematic drawing and are explained in the following description. Fig. 1 schematically shows in meridional section a projection exposure system for EUV projection lithography, Fig. 2a-b schematic sectional views of a mirror of the projection exposure system of Fig. 1 with a hollow structure having a plurality of cooling channels, Fig. 2c a schematic representation of the mirror of Fig. 2a,b during the production of the hollow structure using a fluid supply device with two different insert components, Fig. 3a-c schematic representations of a first example of the fluid supply device with an insert component with several guide channels in the form of bent tubes for guiding flexible fluid lines, as well as Fig. 4a,b schematic representations of a second example of the fluid supply device in which the insert component was manufactured by additive manufacturing.

[0042] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0043] In the following, with reference to Fig. Figure 1 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. The description of the basic structure of the projection exposure system 1 and its components is not intended to be limiting.

[0044] 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.

[0045] 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.

[0046] In Fig. 1 shows a Cartesian xyz coordinate system for explanation. 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 the Fig. 1 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0047] 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.

[0048] 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).

[0049] 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 (GI), 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.

[0050] 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.

[0051] 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 planar 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. Of these facets 21, Fig. 1 shows only a few examples. A second facet mirror 22 is arranged downstream of the first facet mirror 20 in the beam path of the illumination optics 4. The second facet mirror 22 comprises a plurality of second facets 23.

[0052] 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.

[0053] 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.

[0054] In the Fig. In the example shown in Figure 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 0.3 or 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0055] The mirrors Mi, just like the mirrors of the illumination optics 4, can have a highly reflective coating for the illumination radiation 16.

[0056] Fig. 2a,b shows, by way of example, a mirror M4 of the projection system 10, which has a monolithic substrate 25. 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, a glass ceramic, e.g., Zerodur®.

[0057] A reflective coating 26 is applied to a surface 25a of the monolithic substrate 25. A portion 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 utilized portion of the reflective coating 26 (not shown). For reflecting the EUV radiation 16, the reflective coating 26 can, for example, comprise a plurality of layer pairs made of materials, each with a different real part of the refractive index, which, at a wavelength of the EUV radiation 16 of 13.5 nm, can be formed, for example, from Si and Mo.

[0058] The substrate 25 has a hollow structure 27 through which a fluid 28 can flow, which in the example shown is water. Fig. 2a, the fluid 28 indicated by an arrow enters the substrate 25 via an inlet opening 29 on a side surface in order to flow through a plurality of cooling channels 31 which form part of the hollow structure 27 in order to thereby cool in particular the surface 25a of the substrate 25 to which the reflective coating 26 is applied.

[0059] For the supply of the fluid 28 to the inlet opening 29 as well as for the discharge of the fluid 28 from a Fig. 2c, the projection exposure system 1 has a temperature control device in the form of a cooling device 32, which is shown very 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 mirror M4 and, for this purpose, has a supply line (not shown) which is fluid-tightly connected to the inlet opening 29.

[0060] The cooling device 32 also has a discharge line (not shown) for discharging the cooling water from the substrate 25 or the hollow structure 27 via the outlet opening. 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 connected to the cooling device 32 for cooling purposes or, if necessary, to other temperature control or cooling devices provided for this purpose.

[0061] As in Fig. 2a, the fluid 28 enters a first cavity 33 of the hollow structure 27 via the inlet opening 29, which forms a fluid distributor and from which a plurality of distributor channels 34 branch off, each of which is connected to one of the plurality of cooling channels 31. The cooling channels 31 are arranged at a distance A of approximately 2 mm to approximately 5 mm from the planar surface 25a of the substrate 25 in the example shown and extend parallel to the surface 25a, i.e. parallel to an XY plane of an XYZ coordinate system. The cooling channels 31 run in a straight line, are aligned parallel, and extend in the longitudinal direction (Y direction) over approximately the entire portion of the surface 25a of the substrate 25 covered by the coating 26 (cf. Fig. 2b). From the cooling channels 31, the fluid 28 flows via a plurality of collector channels 36 to a fluid collector, which in the Fig. 2b, is designed as a second cylindrical cavity 35. The fluid 28 exits the hollow structure 27 of the substrate 25 via the outlet opening 30. In the example shown, the cooling channels 31 run straight in the horizontal direction (X direction), and the distribution channels 34 and the collector channels 36 run straight in the vertical direction (Z direction). Accordingly, the longitudinal axes of the cooling channels 31 are aligned at an angle of 90° to the distribution channels 34 and the collector channels 36, respectively. However, such an alignment is not mandatory.

[0062] For the production of the Fig. 2a-c, the procedure is as follows: First, the two circular-cylindrical cavities 33, 35, which form the fluid distributor and the fluid collector, are introduced into the material of the substrate 25 by mechanical processing (e.g., by grinding or ultrasonic grinding). Subsequently, the substrate 25 is immersed in a liquid bath, more precisely, in a water bath, whereby a fluid 28 in the form of water enters and fills the cavity 33 of the fluid distributor through the inlet opening 28 and the cavity 35 of the fluid collector through the outlet opening 30. Starting from the respective cavities 33, 35 filled with the fluid 28, a plurality of short channel sections 37 adjacent to the cavities 33, 35 are created by multi-photon laser ablation, as shown in Fig. 2c can be seen.

[0063] To produce the channel sections 37, a plurality of pulsed laser beams are irradiated from the surface 25a of the substrate 25 through the material of the substrate 25 onto the upper side of the cavity 33, which forms the fluid distributor, and are focused there. With each irradiated pulsed laser beam, the focus region is moved in a movement pattern with a plurality of parallel ablation paths offset from one another in the Z direction, forming an ablation front 30a oriented at an angle of approximately 45° to the thickness direction Z of the substrate 25. To offset the ablation paths in the Z direction, the focus position of the irradiated laser beam is changed in the Z direction.

[0064] Starting from the point at the top of the cavity 33 from which the channel section 37 originates, the ablation front 30a is displaced several times in the thickness direction (Z-direction) relative to the substrate 25 in order to ablate the material of the substrate 25 and form the channel section 37. During the displacement, the ablation front 30a can remain stationary, and the substrate 25 is displaced downward in the Z-direction until the ablation front 30a is at a distance of approximately 20-40 mm from the top of the cavity 33. To produce a channel section 37 with a greater length by multi-photon laser ablation, it is generally necessary for the ablation front 30a to be locally flushed with a fluid 28, as described in more detail below. The production of channel sections 37, which extend from the cavity 35 forming the fluid collector, is carried out in a corresponding manner by multi-photon laser ablation.A further ablation front 30b formed in this way is also aligned at approximately 45° to the thickness direction of the substrate 25 or to the XY plane, but is mirrored with respect to the XZ plane compared to the ablation front 30a described above.

[0065] To Fig. 2a,b, the substrate 25 is removed from the liquid bath and the liquid 28 is removed from the cavities 33, 35. For the production of the remaining hollow structure 27, a fluid supply device 38 is used to supply a fluid 28 in the form of water to the respective ablation front 30a, 30b, which is shown very schematically in Fig. 2c. The fluid supply device 38 has two insert components 39, 40 and a plurality of flexible fluid lines 41. In the example shown, the fluid supply device 38 has seven fluid lines 41. The fluid lines 41 are connected to a fluid supply device 43 of the fluid supply device 38, which has a pump for pumping the fluid 28 into the flexible fluid lines 41 at a pressure that is generally several bar. The fluid supply device 43 also has a tracking device 44, which serves to track, or more precisely, to push, the flexible fluid lines 41 when the ablation fronts 30a, 30b are moved in the substrate 25 to form the hollow structure 27. The tracking device 44 can, for example, have a spool or the like, onto which a section of a respective flexible fluid line 41 is wound.For tracking, the coil can be rotated at a constant angular velocity corresponding to the speed of movement of the removal front. It is understood that the tracking device 44 can also be designed in other ways.

[0066] To produce the hollow structure 27, the first rod-shaped, cylindrical insert component 39 is inserted through the inlet opening 29 into the first cavity 33 until one end face rests against the end of the first cavity 33, which forms a blind bore. The insert component 39 is aligned in the circumferential direction such that openings 46 formed in a lateral surface 45 of the insert component 39 are positioned at those points on the wall of the cavity 33 from which a number of channel sections 37 corresponding to the number of openings 46 emanate or branch off from the cavity 33. The alignment of the insert component 39 in the circumferential direction can also be achieved by providing a laterally projecting section on the end face 39a of the rod-shaped insert component 39 (cf. Fig. 2c), which serves as a spring and which engages in a correspondingly shaped groove on the side surface of the substrate 25 (in Fig. 2b shown in dashed lines).

[0067] In order to introduce the flexible fluid lines 41 into the channel sections 37, the insert component 39 has seven guide channels 47 in the example shown (cf. Fig. 3a-c). It is understood that the insert component 39 may also have a larger or smaller number of guide channels 47. As in Fig. 3a, which shows the insert component 39 in a plan view of its front side 39a (cf. Fig. 2c), six of the guide channels 47 are arranged around a central guide channel 47. The guide channels 47 are the Fig. The example shown in Figures 3a-c involves stainless steel pipes embedded or cast in a solid material 48, which defines the diameter D of the insert component 39, which in the example shown is approximately 9 mm. The diameter H of the cylindrical cavity 33, or more precisely of its inner wall 33a, is somewhat larger and is approximately 10 mm. The inner diameter d of each guide channel 47 is approximately 2 mm. The (inner) diameter F of each flexible fluid line 41 is approximately 1 mm.

[0068] As in Fig. As can be clearly seen in Figure 3a, a respective fluid line 41 runs through the center of a respective guide channel 47. An annular gap 49 is located between the fluid line 41 and an inner wall 47a of each guide channel 47. The annular gap 49 serves to return the fluid 28, which is supplied to a respective ablation front 30a, 30b through the flexible fluid line 41. The returned fluid 28 exits at the end face 39a of the insert component 39 and is discharged from there.

[0069] As in Fig. As can be seen in Figure 3b, a respective guide channel 47 of the insert component 39 has a rounded section 50 to change the orientation of the flexible fluid line 41 from a direction parallel to the longitudinal direction (corresponding to the Y direction) of the insert component 39 to a direction perpendicular thereto, so that the flexible fluid line 41 can exit at a respective opening 46 on the lateral surface 45 of the rod-shaped insert component 39. The rounded section 50 is produced by bending a respective stainless steel tube that forms the guide channel 47.

[0070] As in Fig. 2c and in Fig. 3c, the openings 46 in the lateral surface 45 of the insert component 39 are arranged along a common line that corresponds to the longitudinal direction (Y-direction) of the insert component 39. This is necessary because the channel sections 37 also run along a common line that corresponds to the longitudinal direction (Y-direction) of the cavity 33. The distance A between adjacent openings 46 on the lateral surface 45 corresponds to the distance between adjacent channel sections 37 in the substrate 25. It is not absolutely necessary for the channel sections 37 and the openings 46 in the lateral surface of the insert component 39 to run along a common line; rather, deviations from such an arrangement along a common line are possible.

[0071] In order to arrange the openings 46 on the lateral surface 45 next to each other in the longitudinal direction, it is necessary to design the guide channels 47 with different lengths and to rotate the curved sections 50 against each other, as shown in Fig. 4a,b, which shows an insert component 39 which differs from the one shown in Fig. 3a-c in that it was manufactured using an additive manufacturing process. Fig. The insert component 39 shown in Figures 4a,b consists of a cylindrical base body in which the guide channels 47 were formed during additive manufacturing.

[0072] The free ends of the fluid lines 41 projecting beyond the outer surface 45 of the insert component 39 (cf. Fig. 4b) protrude into the channel sections 37 during operation of the fluid supply device 38. For the production of the Fig. In the part of the hollow structure 27 shown in dashed lines in Figure 2c, an ablation front 30a, 30b is generated at the end faces of the already formed channel sections by irradiating pulsed laser radiation, and the ablation front is moved relative to the substrate 25 by displacing the substrate 25 downward in the Z direction until the ablation front 30a is at the level of the horizontally extending cooling channel 31. Alternatively, for example, the focus position of the irradiated pulsed laser radiation can be shifted upward by the same amount at all points along the ablation front 30a in order to move the ablation front 30a in the substrate 25, while the substrate 25 itself remains stationary.

[0073] To form the horizontal cooling channel 31, the ablation front 30a, which is aligned at approximately 45° to the thickness direction (Z direction) of the substrate 25 or to the irradiation direction of the pulsed laser beam, is displaced in the longitudinal direction (X direction) of the cooling channel 31 until it is located approximately in the center of the cooling channel 31. In this case, the substrate 25 is typically stationary, and the optics for irradiating the laser beams onto the substrate 25 are suitably adjusted or moved to displace the ablation front 30a in the horizontal direction.

[0074] Using a further insert component of a further fluid supply device (not shown), a plurality of seven collector channels 35 are typically created by multi-photon laser ablation, typically in parallel, starting from the second cavity 35, by displacing the substrate 25 downwards or by displacing the focus position of the irradiated pulsed laser radiation upwards by a constant amount at each point of the ablation front 30b, wherein the substrate 25 remains stationary. The ablation front 30b is subsequently moved in the Y direction while the substrate 25 is at rest. Approximately in the middle of each cooling channel 31, which, for example, has a length of approx.400 mm, there is an overlap of the two removal fronts 30a, 30b, whereby a continuous cooling channel 31 is created, which is connected by the distributor channel 34 to the first cavity 33 serving as a fluid distributor and by the collector channel 36 to the second cavity 35 serving as a fluid collector.

[0075] In the manner described above, it is possible to produce seven distribution channels 34, cooling channels 31 and collector channels 36 simultaneously, whereby the time required for the production of the hollow structure 27 can be significantly reduced. In order to produce the remaining seven distribution channels 34, cooling channels 31 and collector channels 36 of the Fig. To produce the hollow structure 27 shown in Figure 2c, the Fig. 2c, in which the openings 46' for the outlet of the fluid lines 41 are offset with respect to the openings 46 of the first insert component 39. The second group of seven distribution channels 34, cooling channels 31, and collector channels 36 is manufactured analogously to the first group, by inserting the second insert component 40 into the first cavity 33.

[0076] It goes without saying that unlike in Fig. 2c shows that the second insert component 40 can have a shorter length than the first insert component 39. If this is the case, a spacer, for example in the form of a solid cylinder, can be inserted into the cavity 33 before the second insert component 40 is inserted, against the end face of which the insert component 40 is brought into contact during insertion. Alternatively, one or more protruding sections on the end face of the insert component 40 can serve as stoppers or as contact surfaces to limit the movement of the second insert component 40 during insertion into the cavity 33. The stoppers, which are attached to the end face of the second insert component 40, can also serve as springs and engage in corresponding grooves on the outside of the substrate 25 in order to suitably align the second insert component 40 in the circumferential direction, as described above.

[0077] With the aid of the fluid supply device 38 described above, in the production of complex hollow structures 27, as shown in Fig. 2c, an automated tracking of the flexible fluid lines 41 to several simultaneously generated ablation fronts 30a, 30a can be performed. In this way, a plurality of structures, for example, cooling channels 31, can be produced in parallel, resulting in a significant time saving and increased productivity in the production of the complex hollow structure 27.

Claims

[1] Fluid supply device (38) for supplying a fluid (28) to at least one ablation front (30a, 30b) during the removal of material by multi-photon laser ablation from a workpiece, comprising: a plurality of flexible fluid lines (41) for supplying the fluid (28) to the at least one ablation front (30a, 30b), and at least one insert component (39, 40) for insertion into a cavity (33, 35) of the workpiece (25), wherein the insert component (39, 40) has a plurality of guide channels (47), in each of which a flexible fluid line (41) is guided in order to supply the fluid (28) to the at least one ablation front (30a, 30b). [2] Fluid supply device according to claim 1, wherein a flow-through gap for returning the fluid (28) from the ablation front (30a, 30b) is formed between the fluid line (41) and a channel wall (47a) of the guide channel (47). [3] Fluid supply device according to claim 1 or 2, wherein the guide channel (47) has at least one rounded section (50) for changing the direction of the flexible fluid line (41). [4] Fluid supply device according to one of the preceding claims, in which the insert component (39, 40) is rod-shaped and the guide channel (47) extends from an end face (48) of the insert component (39) to a lateral surface (45) of the insert component (39). [5] Fluid supply device according to claim 4, wherein the guide channels (41) open into openings (46) on the lateral surface (45) of the insert component (39). [6] Fluid supply device according to claim 4 or 5, wherein the rod-shaped insert component (39) is cylindrical. [7] Fluid supply device according to one of the preceding claims, wherein the at least one guide channel (47) has a diameter (d) between 1 mm and 4 mm. [8] Fluid supply device according to one of the preceding claims, wherein the at least one fluid line (41) has an outer diameter (F) of 1 mm or less. [9] Fluid supply device according to one of the preceding claims, further comprising: a fluid supply device (43) for supplying the fluid (28) to the at least one flexible fluid line (41). [10] Fluid supply device according to one of the preceding claims, further comprising: at least one tracking device (44) for the automated tracking of the at least one flexible fluid line (41) during a movement of the ablation front (30a, 30b) in the material of the workpiece (25). [11] Method for supplying a fluid (28) to at least one ablation front (30a, 30b) during the removal of material by multi-photon laser ablation from a workpiece by means of a fluid supply device (38) according to one of the preceding claims, comprising: Inserting the insert component (39, 40) into a cavity (33, 35) of the workpiece (25), and Supplying the fluid (28) to the at least one ablation front (30a, 30b) through the at least one flexible fluid line (41) which is guided in the at least one guide channel (47) of the insert component (39, 40). [12] Method according to claim 11, wherein before the insertion of the insert component (39, 40) the cavity (33, 35) is filled with a fluid (28) and starting from the cavity (33, 35) filled with the fluid (28), a plurality of channel sections (37) adjacent to the cavity (33, 35) are formed by multi-photon laser ablation. [13] Method according to claim 12, wherein after the insertion of the insert component (39, 40) into the cavity (33, 35), a plurality of ablation fronts (30a, 30b) are generated starting from the channel sections (37) and moved in the material of the workpiece (25) to form a plurality of channels (31, 34, 35), wherein the plurality of flexible fluid lines (41) are guided in the material of the workpiece (25) during the movement of the ablation fronts (30a, 30b).

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