DE102021214318A1 - Fluid delivery apparatus and method for delivering a fluid to at least one ablation front - Google Patents

Abstract

The invention relates to a fluid supply device (38) for supplying a fluid (28) to at least one ablation front when removing material by multi-photon laser ablation from a workpiece, preferably from an in particular monolithic substrate (25) for an EUV mirror, comprising: at least one flexible fluid line (41), preferably a plurality of flexible fluid lines (41), for supplying the fluid (28) to the at least one ablation front, and at least one insertion component (39, 40) for insertion into a cavity (33, 35) of the workpiece (25), wherein the insert component (39, 40) has at least one guide channel in which the at least one flexible fluid line (41) is guided in order to supply the fluid (28) to the at least one ablation front. The invention also relates to a method for supplying a fluid (28) to at least one ablation front when removing material from a workpiece by multi-photon laser ablation, preferably from an in particular monolithic substrate (25) for an EUV mirror (M4), by means such a fluid supply device (38), 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 through the at least one flexible fluid line ( 41), which is guided in the at least one guide channel of the insert component (39, 40).

Description

Background of the Invention

The invention relates to a fluid supply device for supplying a fluid to at least one ablation front when material is removed by multi-photon laser ablation from a workpiece, preferably from an in particular monolithic substrate for an EUV mirror. The invention also relates to a method for supplying a fluid to the at least one ablation front when removing 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.

In EUV lithography, projection exposure systems are used to produce semiconductor components, which are operated with short-wave radiation, so-called EUV radiation, at an operating wavelength of between approximately 5 nm and approximately 30 nm. Due to the short-wave radiation, coated mirrors (EUV mirrors) are used for beam guidance and focusing, which have a substrate made of a material with a very low coefficient of thermal expansion. The material of the substrate can be, for example, titanium-doped quartz glass, which is known under the trade name "ultra-low-expansion" (ULEO) glass. However, the material of the substrate can also be certain glass ceramics that have a low coefficient of thermal expansion and are offered, for example, under the trade names “Clearceram®” or “Zerodur®”. The productivity in the manufacture of the exposed wafers depends heavily on the power of the EUV light source that is used to generate the EUV radiation. However, a high power of the radiation impinging on the EUV mirror leads to an increased thermal load on the EUV mirror. Despite the extremely low coefficient of thermal expansion, the heat output introduced into the substrate increasingly leads to shape deviations of the high-precision mirror surfaces that are no longer tolerable. Active cooling of the EUV mirrors is therefore necessary in order to meet the demand for growing productivity and thus ever more powerful EUV light sources.

Due to the fact that the typical substrate materials have a very low thermal conductivity and material strengths or thicknesses in the order of magnitude of several centimeters, it is necessary to dissipate the heat generated 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 in the volume of the substrate, which have a comparatively large cross section of usually more than approx. 1 mm and which run at a small distance below the optical surface of the substrate which has a reflective coating applied to reflect EUV radiation.

Substrate materials for EUV mirrors, eg titanium-doped quartz glass (ULE®), are successively built up from SiO ₂ and TiO ₂ by flame hydrolysis, among other things. The creation of hollow structures in the form of cooling channels can therefore only take place afterwards in the volume of the workpiece material. Conventionally, hollow structures can be realized in hard and brittle materials such as glass or (glass) ceramics by mechanical processing, for example by drilling (for example using a diamond drill bit) or ultrasonic-based removal. 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 tension and damage to the material, especially with tactile methods.

In the DE102015210286A1 and in the WO2016192938A1 describes a method and an associated device in which workpiece material is removed within a workpiece, for example a plane-parallel plate, in a respective focus area by multi-photon absorption. During the processing, the rear side of the workpiece is brought into contact with a flowable liquid that is transparent to the laser radiation, at least in a processing area that includes the focus area. A nozzle can be used for this purpose, which is connected to a liquid line in order to carry away the ablation products and to cool the workpiece. The liquid can be directed to the back of the workpiece in the form of a free liquid jet with the aid of an adjustable nozzle, or the workpiece can be (partially) immersed in a liquid bath.

In the WO2016192938A1 it is described that this method can be used to produce cylindrical through-holes with a diameter of approx. 500 µm in a glass with a thickness in the range of millimeters by moving the laser beam with the help of a scanner with a specified movement pattern in a processing plane parallel to the workpiece surface . For the production of the through hole, the processing plane is shifted several times in the thickness direction of the workpiece and the scanning process is carried out with a specified movement pattern repeated several times. 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).

That in the DE102015210286A1 or in the WO2016192938A1 The method described 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 manufacture of hollow structures with a more complex geometry than a straight, cylindrical through-hole. This is the case, for example, with the substrates described above for mirrors for EUV lithography, into which hollow structures in the form of channels are to be introduced, which generally do not run in a straight line.

Even when producing complex hollow structures, which can have branches, for example, 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 and to cool the workpiece locally and avoid thermal stresses that could lead to damage of the material and the occurrence of stress birefringence.

object of the invention

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

This object is achieved by a fluid supply device of the type mentioned at the outset, comprising: at least one flexible fluid line, preferably 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 insertion component for insertion into one Cavity of the workpiece, wherein the insert component has at least one guide channel in which the at least one flexible fluid line is guided in order to supply the fluid to the at least one ablation front.

The fluid supply device according to the invention has at least one flexible fluid line 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, and which can be guided along the ablation front as it moves through the workpiece. In order to position the flexible fluid line, more precisely its free end from which the fluid exits, at a predetermined point within the substrate, the flexible fluid line is guided in the fluid supply device according to the invention in a guide channel of an insert component that is inserted into a cavity in the workpiece becomes.

This is particularly favorable when one or more structures formed by multi-photon laser ablation branch off from a wall of the cavity, since in this case the respective end of the fluid line can be connected to a point on the wall with the aid of the insert component or the guide channel of the cavity from which the structure emanates and can be tracked when forming the structure of the ablation front.

It is possible for a short section of the respective structure branching off from the cavity to be produced by multi-photon laser ablation before the insertion component is inserted into the cavity. In order to supply a fluid to the ablation front formed in this way, 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 approx. 20-40 mm from the wall of the cavity, immersion in the liquid bath is usually no longer sufficient, since the material removed can no longer be transported away to a sufficient extent and the ablation process can no longer be carried out comes to a standstill. For the production of structures that branch off from the cavity and have a length greater than approx. 20-40 mm, it is necessary to track the fluid with the aid of a flexible fluid line when the ablation front moves.

A flexible fluid line can also follow the ablation front without an insert component, as long as the hollow structure that is produced by the multi-photon ablation does not branch or has a geometry that is otherwise too complex. However, as described above, the flexible fluid line can be positioned at the point at which a structure should start or branch off from the cavity with the help of the insert component. With the help of the insert component, the supply of the fluid to the ablation front can therefore also be ensured in the case of a hollow structure that has branches, without the flexible fluid line(s) having to be manually threaded into the structure(s) branching off from the cavity is.

In multi-photon laser ablation, pulsed laser radiation, usually ultra-short pulse laser radiation, is used to form a hollow structure. through the material of the substrate onto 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 emanate. During multi-photon laser ablation, an ablation front is generated which, starting from this point, is moved through the material of the substrate in order to form the hollow structure. For details on removing material using multi-photon laser ablation, see WO2016192938A1 referenced, which is incorporated by reference in its entirety into the content of this application.

For the production of hollow structures with complex geometries, this can be done in the WO2016192938A1 The method described can be modified by the removal front or the processing plane not being aligned perpendicularly to the irradiation direction of the pulsed laser radiation, which typically runs along a thickness direction of the workpiece, but being tilted with respect to a plane perpendicular to the irradiation direction, as described below. In this way, non-rectilinear hollow structures with undercuts can also be produced by multi-photon laser ablation.

The fluid is typically a liquid, for example water, which emerges from the flexible fluid line at a comparatively high pressure, usually at several bars. Instead of a liquid, a gas, for example compressed air, can also be brought into contact with the ablation front in order to transport away the ablation products. A nozzle for exiting the fluid can be attached to the free end of the flexible fluid line (or a hose), but this is not absolutely necessary.

The workpiece is preferably an in particular monolithic substrate for an EUV mirror. A monolithic substrate is formed in one piece and does not have a joining surface on which two or more sub-bodies of the substrate are connected to one another. As described above, hollow structures in such a monolithic substrate cannot easily be produced by mechanical processing, e.g. by drilling or by grinding, in the hard and brittle glass material, which is, for example, titanium-doped quartz glass or a glass-ceramic can act. The cavity described above can be produced by mechanical processing, for example the cavity can be a bore which is milled into the substrate. In principle, however, it is also possible for the cavity to be produced by multi-photon laser ablation, even if this method is time-consuming when producing cavities with large diameters.

In one embodiment, 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 that emanate from the cavity, it is therefore favorable to produce the plurality of channels or other structures at the same time. For this purpose, several pulsed laser beams can be irradiated simultaneously through the volume of the workpiece in order to simultaneously form several ablation fronts at which the material of the workpiece is removed, whereby several structures or channels branching off from the cavity can be produced simultaneously.

The simultaneous generation of several removal fronts requires the simultaneous supply of the fluid to the removal fronts with the aid of a corresponding number of guide channels or flexible fluid lines, which track the respective removal fronts. Ideally, all structures branching off from the cavity can be produced simultaneously. If the number of branching structures is too large, they can be divided into several groups, which are each processed together at the same time. Differently designed insert components can be used for the production of a respective group of structures.

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 that is selected in such a way that the fluid supplied to the removal front in the fluid line can be discharged again via the gap that can be flowed through. 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.

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 that branch 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. Does the respective guide channel go 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 ideally takes place by guiding the fluid line along a rounded or curved section of the guide channel. A change in direction of the flexible fluid line preferably takes place at the rounded section at an obtuse angle, ie at an angle that is greater than 90°.

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 straight channel, preferably of constant diameter, which extends into the volume of the workpiece from an opening on one side of the workpiece. In this case, the insert component is inserted into the cavity by being pushed into the cavity 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 routed away from the workpiece and connected to a supply device for the fluid, which has a pump or the like. With the aid of the rounded section of the guide channel described above, a respective flexible fluid line can be guided from the end face of the insert component to the outer surface of the insert component.

In a further development of this embodiment, the guide channels on the jacket side of the insert open into openings which are preferably arranged next to one another in the longitudinal direction of the insert and which are arranged at equal distances from one another in particular in the longitudinal direction of the insert. An arrangement of the openings next to one another in the longitudinal direction of the insert component means that the openings run along a common straight line or line, which 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 favorable when a plurality of structures branching 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 arranged equidistantly in the longitudinal direction of the insert component, i.e. at equal distances from one another.

In a 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 that 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 fixed. The insert component is additionally aligned or rotated in such a way that the openings in the lateral surface of the insert component are positioned in the circumferential direction in such a way that they correspond to the points from which the structures branching off from the cavity are to emanate. Furthermore, the end face of the insert component can have a protruding section (tongue) which snaps into a notch or a groove in the workpiece in order 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 with. In this way, the length of the insert component can be reduced.

In a further embodiment, the at least one guide channel has an (internal) diameter of between 1 mm and 4 mm. The structures that emanate from the cavity generally have a significantly smaller diameter than the insert component. This is favorable since in this way a plurality of guide channels running within the insert component can be accommodated in the insert component.

In a further embodiment, the at least one fluid line has an outer diameter of 1 mm or less. As has been described above, it is generally necessary for a gap to remain 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.

The insert component can be designed in different ways. For example, the guide channels as tubes, such as stainless steel tubes or plastic tubes, be formed, which are bent or are bent to the or to form the rounded sections. The guide channels in the form of tubes, for example stainless steel tubes or plastic tubes, can be bundled and cast in a suitable material, for example, in order to produce an insert component with a desired geometry, for example in the manner of a cylinder.

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

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 favorable to let the fluid exit the fluid line at a comparatively high pressure of several bars. It is therefore favorable to supply the fluid to the flexible fluid line with the aid of a pump which generates a correspondingly high pressure and which is part of the fluid supply device.

In a further embodiment, the fluid supply device comprises at least one tracking device for automated tracking of the at least one flexible fluid line when the ablation front moves 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 takes place at the processing speed. For the tracking, the flexible fluid line is pushed in, for example by being unwound from a spool or the like at a constant speed. In order to track the flexible fluid line, it is necessary for the material of the fluid line to have sufficient shearing rigidity, 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 adjusted speed.

Another aspect of the invention relates to a method for supplying a fluid to at least one ablation front when removing material from a workpiece by multi-photon laser ablation, preferably from an in particular monolithic substrate for an EUV mirror, by means of a fluid supply device as above described, the method comprising: 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, which is guided in the at least one guide channel of the insert component. As has been described above, the flexible fluid line can automatically follow the ablation front with the aid of a fluid supply device, which is designed as described above, when it moves through the workpiece.

In one variant, before the insertion component is inserted, the cavity is filled with a fluid and, starting from the cavity filled with the fluid, a plurality of channel sections adjoining the cavity are formed by multi-photon laser ablation. For the production of comparatively short sections of channels or other structures that emanate from or branch off from the cavity, typically no local supply of a fluid to the ablation front using a (flexible) fluid line is required: With a length of the channel section that is generally in the order of no more than approx. 20-40 mm, it is sufficient if the cavity as a whole - and thus also the channel sections formed during multi-photon absorption - are filled with a fluid. For this purpose, the workpiece is typically partially immersed in a liquid or in a liquid bath, usually in a water bath, with the fluid.

In a further development of this variant, after the insert component has been inserted into the cavity, starting from the end faces of the channel sections, a plurality of ablation fronts are produced and moved in the material of the workpiece in order to produce a plurality of channels, with the majority of the flexible fluid lines moving during the movement of the Ablation fronts are tracked in the material of the workpiece.

If the workpiece is a substrate for an EUV mirror, it can have two cavities, for example, which serve as fluid distributors and fluid collectors and in each of which an insert component is inserted. The two cavities are fluidically connected to one another by a plurality of channels which branch off from the first cavity and open into the second cavity. Starting from each In one of the two cavities, a first or second channel section, which corresponds to approximately half the length of a respective channel, can be produced by multi-photon laser ablation. Approximately in the middle of the length of the channel, the removal fronts of the two channel sections overlap during manufacture, as a result of which a continuous channel is created which connects the fluid distributor to the fluid collector.

If the channels are 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 starting from the fluid distributor, which has a comparatively large distance from the optical surface of the EUV mirror, in the vicinity of the surface. In a channel section that forms a cooling channel, the fluid, typically in the form of cooling water, is conducted along the surface before the fluid is conducted away from the surface in a collector channel and fed to the fluid collector.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can each be realized individually or together in any combination in a variant of the invention.

character list

• 1 schematisch im Meridionalschnitt eine Projektionsbelichtungsanlage für die EUV-Projektionslithografie,
• 2a-b schematische Schnittdarstellungen eines Spiegels der Projektionsbelichtungsanlage von 1 mit einer Hohlstruktur, die eine Mehrzahl von Kühlkanälen aufweist,
• 2c eine schematische Darstellung des Spiegels von 2a,b bei der Herstellung der Hohlstruktur unter Verwendung einer Fluidzuführungsvorrichtung mit zwei unterschiedlichen Einlegebauteilen,
• 3a-c schematische Darstellungen eines ersten Beispiels der Fluidzuführungsvorrichtung mit einem Einlegebauteil mit mehreren Führungskanälen in Form von gebogenen Rohren zur Führung von flexiblen Fluidleitungen, sowie
• 4a,b schematische Darstellungen eines zweiten Beispiels der Fluidzuführungseinrichtung, bei der das Einlegebauteil durch additive Fertigung hergestellt wurde.

Exemplary embodiments are shown in the schematic drawing and are explained in the following description. It shows

• 1 a schematic meridional section of a projection exposure system for EUV projection lithography,
• 2a-b schematic sectional views of a mirror of the projection exposure system from 1 with a hollow structure having a plurality of cooling channels,
• 2c a schematic representation of the mirror of 2a,b in the production of the hollow structure using a fluid supply device with two different insert components,
• 3a-c schematic representations of a first example of the fluid supply device with an insert component with a plurality of guide channels in the form of bent tubes for guiding flexible fluid lines, and
• 4a,b schematic representations of a second example of the fluid supply device, in which the insert component was produced by additive manufacturing.

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

The following are referring to 1 the essential components of an optical arrangement for EUV lithography in the form of a projection exposure system 1 for microlithography are described by way of example. The description of the basic structure of the projection exposure system 1 and of its components is not to be understood as limiting here.

One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, 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 lighting system does not include the light source 3 .

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 .

In 1 a Cartesian xyz coordinate system is drawn in for explanation. The x-direction runs perpendicular to the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scanning direction is in the 1 along the y-direction. The z-direction runs perpendicular to the object plane 6.

The projection exposure system 1 comprises a projection system 10. The projection system 10 is used to image the object field 5 in an image field 11 in an image plane 12. A structure on the reticle 7 is imaged on a light-sensitive layer of a wafer arranged in the region of the image field 11 in the image plane 12 13. 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 via the reticle displacement drive 9 on the one hand and the wafer 13 on the other hand via the wafer displacement drive 15 can be synchronized with one another.

The radiation source 3 is an EUV radiation source. The radiation source 3 emits in particular EUV radiation 16, which also referred to below as useful radiation, illumination radiation or illumination light. In particular, the useful radiation has 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, plasma generated with the aid of a laser) 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 (free-electron laser, FEL).

The illumination radiation 16 emanating from the radiation source 3 is bundled 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 in grazing incidence (Grazing Incidence, GI), i.e. with angles of incidence greater than 45°, or in normal incidence (Normal Incidence, NI), i.e. with angles of incidence less than 45° become. 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.

After the collector mirror 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focus plane 18. The intermediate focus 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.

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

The illumination optics 4 thus forms a double-faceted system. This basic principle is also known as a honeycomb condenser (Fly's Eye Integrator). The individual first facets 21 are imaged in the object field 5 with the aid of the second facet mirror 22 . The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5.

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

At the in the 1 illustrated example, the projection system 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi 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 involves doubly obscured optics. The projection optics 10 has a numerical aperture on the image side which is greater than 0.3 or 0.5 and which can also be greater than 0.6 and which can be 0.7 or 0.75, for example.

Like the mirrors of the illumination optics 4, the mirrors Mi can have a highly reflective coating for the illumination radiation 16.

2a,b FIG. 12 shows, by way of example, a mirror M4 of the projection system 10 which has a monolithic substrate 25. FIG. 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 coefficient of thermal expansion, for example from a glass ceramic, for example from Zerodur®.

On a surface 25a of the monolithic substrate 25, a reflective coating 26 is applied. A portion of the surface 25a, which is within the reflective coating 26, is struck by the EUV radiation 16 of the projection system 10 and forms an optically used portion (not shown) of the reflective coating 26. The reflective coating 26 can be used to reflect the EUV radiation 16 have, for example, a plurality of pairs of layers made of materials, each with a different real part of the refractive index, which can be formed from Si and Mo, for example, at a wavelength of 13.5 nm for EUV radiation 16 .

The substrate 25 has a hollow structure 27 through which a fluid 28 can flow, which in the example shown is water. This in 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 in this way to cool the surface 25a of the substrate 25 in particular , to which the reflective coating 26 is applied.

For the supply of the fluid 28 to the inlet opening 29 and for the discharge of the fluid 28 from an in 2c illustrated outlet opening of the substrate 25, the projection exposure system 1 has a temperature control device in the form of a cooling device 32, which is shown very schematically in 1 is shown. 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 connected to the inlet opening 29 in a fluid-tight manner.

The cooling device 32 also has a discharge line (not shown) in order to discharge the cooling water from the substrate 25 or from the hollow structure 27 via the outlet opening. The other mirrors M1-M3, M5, M6 of the projection system 10 and the mirrors of the illumination system 2 can also be connected to the cooling device 32 for cooling or possibly to other temperature control or cooling devices provided for this purpose.

As in 2a As can be seen, the fluid 28 enters a first cavity 33 of the hollow structure 27 via the inlet opening 29, which cavity forms a fluid distributor and from which a plurality of distribution 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 about 2 mm to about 5 mm from the flat surface 25a of the substrate 25 in the example shown and extend parallel to the surface 25a, ie parallel to an XY plane of an XYZ coordinate system . The cooling channels 31 run in a straight line, are aligned in parallel and extend in the longitudinal direction (Y-direction) over almost the entire partial area of the surface 25a of the substrate 25 covered by the coating 26 (cf. 2 B) . The fluid 28 flows from the cooling ducts 31 via a plurality of collector ducts 36 to a fluid collector, which in 2 B shown example is formed as a second cylindrical cavity 35. The fluid 28 emerges from the hollow structure 27 of the substrate 25 via the outlet opening 30 . In the example shown, the cooling channels 31 run in a straight line in the horizontal direction (X-direction) and the distribution channels 34 and the collector channels 36 run in a straight line in the vertical direction (Z-direction). Correspondingly, the longitudinal axes of the cooling channels 31 are aligned at an angle of 90° to the distribution channels 34 or to the collector channels 36 . However, such an orientation is not absolutely necessary.

For the production of the 2a-c The procedure for the hollow structure shown 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 (eg by grinding or by 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 through the inlet opening 28 into the cavity 33 of the fluid distributor and through the outlet opening 30 into the cavity 35 of the fluid collector and fills them . Starting from the respective cavities 33, 35 filled with the fluid 28, a plurality of short channel sections 37 adjoining the cavities 33, 35 are produced by multi-photon laser ablation, as is shown in 2c can be seen.

To produce the channel sections 37, a plurality of pulsed laser beams are radiated 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 a pulsed laser beam that is radiated in, the focus area is moved in a movement pattern with a plurality of parallel ablation paths that are offset from one another in the Z direction and form an ablation front 30a that is aligned at an angle of approximately 45° to the thickness direction Z of the substrate 25 . For the offset of the ablation paths in the Z-direction, the focus position of the irradiated laser beam is changed in the Z-direction.

Starting from the point at the top of the cavity 33 from which the channel section 37 emanates, the ablation front 30a is shifted several times in the thickness direction (Z-direction) relative to the substrate 25 in order to remove the material of the substrate 25 and to form the channel section 37. During the displacement, the ablation front 30a can remain stationary and the substrate 25 is displaced downwards 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. For the production of a channel section 37 with a greater length by multi-photon laser ablation, it is generally necessary for the ablation front 30a to be flushed locally with a fluid 28, as will be described in more detail below. The manufacture of Channel sections 37 emanating from the cavity 35 forming the fluid collector are made 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 in relation to the ablation front 30a described above with respect to the XZ plane.

To the in 2a,b To form the hollow structure 27 shown, 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 2c is shown. 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 in order to pump the fluid 28 into the flexible fluid lines 41 at a pressure which is generally several bars. The fluid supply device 43 also has a tracking device 44 which is used for tracking, more precisely for pushing the flexible fluid lines 41 when the ablation fronts 30a, 30b are moved in the substrate 25 in order to form the hollow structure 27. The tracking device 44 can have a coil or the like, for example, on which a section of a respective flexible fluid line 41 is wound. For the tracking, the coil can be rotated at a constant angular velocity, which corresponds to the velocity of the movement of the ablation front. It goes without saying that the tracking device 44 can also be designed in a different way.

For the production of the hollow structure 27, the first rod-shaped, cylindrical insertion component 39 is inserted through the inlet opening 29 into the first cavity 33 until one end of it rests against the end of the first cavity 33, which forms a blind hole. 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 from the cavity 33 or branch off. The orientation of the insert component 39 in the circumferential direction can also be achieved by providing a laterally protruding section on the end face 39a of the rod-shaped insert component 39 (cf. 2c ), which serves as a spring and which engages in a correspondingly shaped groove on the side surface of the substrate 25 (in 2 B shown dashed).

In order to insert the flexible fluid lines 41 into the channel sections 37, the insert component 39 has seven guide channels 47 in the example shown (cf. 3a-c ). It goes without saying that the insert component 39 can also have a larger or smaller number of guide channels 47 . As in 3a it can be seen that the insert component 39 in a top view of its end face 39a (cf. 2c ) shows, six of the guide channels 47 are arranged around a central guide channel 47. The guide channels 47 are in 3a-c shown example to stainless steel tubes that are embedded or cast in a solid material 48, which defines the diameter D of the insert component 39, which is about 9 mm in the example shown. The diameter H of the cylindrical cavity 33, more precisely of its inner wall 33a, is slightly larger and is approximately 10 mm. The inner diameter d of a respective guide channel 47 is approximately 2 mm. The (internal) diameter F of a respective flexible fluid line 41 is approximately 1 mm.

As in 3a is clearly visible, a respective fluid line 41 runs in the middle of a respective guide channel 47. There is an annular gap 49 between the fluid line 41 and an inner wall 47a of a respective guide channel 47. The annular gap 49 is used to return the fluid 28, which flows through the flexible Fluid line 41 of a respective ablation front 30a, 30b is supplied. The returned fluid 28 exits at the end face 39a of the insert component 39 and is discharged from there.

As in 3b As can be seen, a respective guide channel 47 of the insert component 39 has a rounded section 50 in order 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 portion 50 is made by bending a respective stainless steel tube that forms the guide channel 47.

As in 2c and in 3c As can be seen, the openings 46 in the lateral surface 45 of the insert component 39 are arranged along a common line which 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, which 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.

In order to arrange the openings 46 next to one another in the longitudinal direction on the lateral surface 45, it is necessary to design the guide channels 47 of different lengths and to rotate the curved sections 50 in relation to one another, as is shown in 4a,b can be clearly seen, which shows an insert component 39, which differs from that in 3a-c shown insert component 39 differs in that it was produced by an additive manufacturing process. This in 4a,b The insert component 39 shown consists of a cylindrical base body in which the guide channels 47 were formed during additive manufacturing.

The free ends of the fluid lines 41 protruding beyond the lateral surface 45 of the insert component 39 (cf. 4b) protrude into the channel sections 37 during operation of the fluid supply device 38 . For the production of the in 2c In the part of the hollow structure 27 shown in dashed lines, an ablation front 30a, 30b is generated on the end faces of the channel sections already formed by irradiation with pulsed laser radiation, and the ablation front is moved relative to the substrate 25 by the substrate 25 being displaced downwards in the Z direction until the ablation front 30a is at the level of the horizontal cooling channel 31 . Alternatively, for example, the focus position of the irradiated pulsed laser radiation can be offset upwards 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.

To form the horizontal cooling channel 31, the ablation front 30a, which is aligned at approx in the middle of the cooling channel 31 is located. In this case, the substrate 25 is typically at rest and the optics for irradiating the laser beams onto the substrate 25 are suitably adjusted or moved in order to shift the removal front 30a in the horizontal direction.

Using a further insert component of a further fluid supply device, not shown, a plurality of seven collector channels 35 are typically generated in parallel, starting from the second cavity 35, by multi-photon laser ablation by moving the substrate 25 downwards or by changing the focus position of the irradiated pulsed Laser radiation at each point of the ablation front 30b is shifted upwards by a constant amount, with the substrate 25 remaining stationary. The ablation front 30b is subsequently moved in the Y direction with the substrate 25 stationary. Approximately in the middle of each cooling channel 31, which can have a length of approx. 400 mm, for example, there is an overlap between the two removal fronts 30a, 30b, resulting in a continuous cooling channel 31 which is connected through the distributor channel 34 to the fluid distributor first cavity 33 and is connected through the collector channel 36 to the second cavity 35 serving as a fluid collector.

In the manner described above, it is possible to produce seven distributor channels 34, cooling channels 31 and collector channels 36 at the same time, as a result of which the time taken to produce the hollow structure 27 can be significantly reduced. To the remaining seven distributor channels 34, cooling channels 31 and collector channels 36 in 2c To produce the hollow structure 27 shown, this can be done in 2c illustrated insert component 40 can be used, in which the openings 46 'for the exit of the fluid lines 41 are offset in relation to the openings 46 of the first insert component 39. The production of the second group of seven distributor channels 34 , cooling channels 31 and collector channels 36 takes place analogously to the production of the first group, in that the second insert component 40 is inserted into the first cavity 33 .

It is understood that unlike in 2c shown, the second insertion component 40 can have a shorter length than the first insertion component 39. If this is the case, before the second insertion component 40 is inserted, a spacer, for example in the form of a solid cylinder, can be inserted into the cavity 33, on the front side of which the Insertion 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 a stop or as contact surfaces in order to limit the movement of the second insert component 40 when it is inserted into the cavity 33 . The stoppers attached to the face of the second insert member 40 may also serve as springs and engage corresponding grooves on the outside of the substrate 25 to properly align the second insert member 40 circumferentially as described above.

With the aid of the fluid supply device 38 described above, in the production of complex hollow structures 27, as shown in 2c are shown, automated tracking of the flexible fluid lines 41 to a plurality of simultaneously generated ablation fronts 30a, 30 take place. In this way, a plurality of structures, for example cooling channels 31, can be produced in parallel, which results in a significant time saving or increase in productivity in the production of the complex hollow structure 27.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102015210286 A1 [0005, 0007]
• WO 2016192938 A1 [0005, 0006, 0007, 0015, 0016]

Claims (14)

Fluid supply device (38) for supplying a fluid (28) to at least one ablation front (30a, 30b) when removing material by multi-photon laser ablation from a workpiece, preferably from an in particular monolithic substrate (25) for an EUV mirror (M4 ), full: at least one flexible fluid line (41), preferably 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), the insert component (39, 40) having at least one guide channel (47) in which the at least one flexible fluid line (41) is guided in order to supply the fluid (28) to the at least one ablation front (30a, 30b). Fluid delivery device claim 1 , In which the insert component (39, 40) has a plurality of guide channels (47), in each of which a flexible fluid line (41) is guided. Fluid delivery device claim 1 or 2 , wherein between the fluid line (41) and a channel wall (47a) of the guide channel (47) a through-flow gap, in particular an annular gap (49), for returning the fluid (28) from the ablation front (30a, 30b) is formed. Fluid supply device according to one of the preceding claims, in which the guide channel (47) has at least one rounded section (50) for changing the direction of the flexible fluid line (41). 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). Fluid delivery device claim 5 , in which the guide channels (41) on the lateral surface (45) of the insert component (39) open into openings (46) which are preferably arranged next to one another in the longitudinal direction (Y) of the insert component (39) and which in particular in the longitudinal direction (Y) of the Insertion component (39) are arranged at equal distances (A) from each other. Fluid delivery device claim 5 or 6 , in which the rod-shaped insert component (39) is cylindrical and preferably has a diameter (D) between 5 mm and 10 mm. Fluid supply device according to one of the preceding claims, in which the at least one guide channel (47) has a diameter (d) of between 1 mm and 4 mm. Fluid delivery device according to one of the preceding claims, in which the at least one fluid line (41) has an outer diameter (F) of 1 mm or less. 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). Fluid supply device according to one of the preceding claims, further comprising: at least one tracking device (44) for automated tracking of the at least one flexible fluid line (41) when the ablation front (30a, 30b) moves in the material of the workpiece (25). Method for supplying a fluid (28) to at least one ablation front (30a, 30b) when removing material by multi-photon laser ablation from a workpiece, in particular from a preferably monolithic substrate (25) for an EUV mirror (M4), using a fluid delivery device (38) according to any one of the preceding claims, comprising: Insertion of the insert component (39, 40) in 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). procedure after claim 12 , in which, prior to 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) by multi-photon laser ablation, a plurality of channel sections (37) adjoining the cavity (33, 35) are formed. procedure after Claim 13 , in which, after the insert component (39, 40) has been inserted into the cavity (33, 35), starting from the channel sections (37), a plurality of ablation fronts (30a, 30b) are produced and moved in the material of the workpiece (25) in order to to form a plurality of channels (31, 34, 35), the plurality of flexible fluid lines (41) being tracked during the movement of the ablation fronts (30a, 30b) in the material of the workpiece (25).

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