WO2023213571A1

WO2023213571A1 - Pressure-reducing unit and euv lithography system

Info

Publication number: WO2023213571A1
Application number: PCT/EP2023/060471
Authority: WO
Inventors: Thomas Monz; Michael KLASNA
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2022-05-04
Filing date: 2023-04-21
Publication date: 2023-11-09
Also published as: DE102022204373A1

Abstract

The invention relates to a pressure-reducing unit (25), comprising: a helical throttle duct (26a, 26a') for reducing the pressure of a liquid (F), wherein the helical throttle duct (26a, 26a') has a plurality of coils (27) which are connected to one another so as to damp vibrations. The invention also relates to an EUV lithography system (1), comprising: at least one component through which a liquid (F) can flow, wherein the component through which the liquid (F) can flow has at least one pressure-reducing unit (25) which is configured as described further above.

Description

Reference to related application

This application claims the priority of the German patent application DE102022204373.1 dated May 4, 2022, the entire disclosure of which is incorporated by reference into the content of this application.

Background of the invention

The invention relates to a pressure reducing unit for reducing the pressure of a fluid, in particular for reducing the pressure of a liquid. The invention also relates to an EUV lithography system which has at least one component, in particular an optical element or a structural component, through which a fluid, in particular a liquid, can flow, wherein the component through which the fluid can flow comprises at least one pressure reducing unit.

Pressure reducing units, also referred to as fluid or flow restrictors or restrictors, are used to reduce the pressure of a fluid, typically a liquid. Pressure reducing units can be used, for example, to balance or control the pressure of parallel, hydraulically connected channels in cooling line systems.

Such cooling line systems are used, for example, in microlithography for cooling optical elements such as lenses or mirrors or for cooling structural elements. Corresponding cooling channels can be guided through both the optical elements and the structural components. The components to be cooled are with the help of Cooling lines connected to each other. In order to ensure the highest possible heat dissipation and good controllability of the cooling system (e.g. a small delay), the components to be cooled are usually flowed through with water as a cooling fluid, since water has a high heat capacity compared to other fluids and is very readily available is. The flowing fluid also ensures improved heat transfer to the surfaces through which the flow passes (forced convection). Due to the flow, an exchange of momentum between the flowing fluid and the walls of the component also takes place in the flow boundary layers. In laminar and stationary flow, this acts as a constant force on the component flowing through (flow pressure loss, see below).

If a critical flow velocity or Reynolds number (critical Reynolds number for pipes: approx. 2300) is exceeded, which depends on the local geometric boundary conditions and the inflow and outflow conditions, small disturbances can no longer be dampened by the viscosity of the medium , so that a disruption of the flow results in persistent periodic and random fluctuations in the flow (turbulence). This turbulence increases the momentum transport from the flow into the component and, depending on the geometry, the medium and the flow condition, can occur as flow-induced vibration (FIV) at, among other things, frequencies that are critical for control technology (e.g. when controlling the position of the mirror). Accelerate components.

Flow-induced vibrations arise from turbulence-induced pressure and momentum fluctuations in the fluid flow. The resulting forces on the walls of the cooling channels lead to dynamic excitation of the components. The development of flow-induced vibrations can be minimized by optimizing the flow guidance and keeping the flow velocities as low as possible. Furthermore, up to ~10% of the hydrodynamic fluctuations (turbulence) couple out into acoustic pressure waves, which travel with The speed of sound of the cooling medium can also continue upstream and, depending on the geometry of the cooling circuit, can be stored in resonance frequencies (similar to organ pipes).

As described above, pressure reducing units in such a cooling system or cooling circuit can, for example, serve to coordinate or compensate for the pressure loss differences in parallel-connected cooling channels or cooling lines in order to suitably adjust the volume flows through the parallel-connected cooling channels.

The pressure loss in a pressure reducing unit can be created in different ways. One possibility is to generate the pressure loss by a cross-sectional jump in the flow cross-section of a channel through which the fluid flows. The jump in cross-section creates a separation of the fluid flow from the wall of the channel through which flow occurs, with the separation of the fluid flow causing turbulence. Another possibility is to generate the pressure loss through viscous friction in flow shear layers of the fluid flow (see above). Depending on the effect used, different design concepts and resulting installation spaces arise.

When reducing the pressure of a fluid, for example by means of a diaphragm that creates a cross-sectional jump with an abruptly changing flow cross-section, strong turbulences are generated before and especially after the diaphragm, which reduce the pressure of the fluid after it flows through the diaphragm. However, the turbulence usually leads to an undesirable dynamic force excitation in the form of the flow-induced vibrations (FIV) of the component through which the fluid flows, described above, which have a negative effect on the entire system. When the pressure of a fluid is lost due to viscous friction, the fluid pressure is reduced by friction of the fluid on the inner wall of a typically tubular flow channel, without turbulence occurring. With this so-called pipe friction, the pressure loss is proportional to the pipe length or the length of the flow channel as well as to the square of the flow velocity and inversely proportional to the flow diameter. Since the pipe diameter cannot be reduced arbitrarily and the flow velocity of the fluid cannot be increased arbitrarily, in order to generate a sufficiently large pressure loss it is generally necessary that the tubular flow channel through which the fluid flows has a comparatively large length to create the desired pressure loss.

The use of a long pipeline inevitably leads to a reduction in its rigidity, i.e. a long pipeline is flexible. Even if a helical pipeline made of steel, for example, is used as a pressure reducing unit in order to reduce the required installation space, undesirable flow-induced vibrations can occur.

Task of the invention

The object of the invention is to provide a pressure reducing unit and an EUV lithography system with reduced flow-induced vibrations.

Subject of the invention

This object is achieved by a pressure reducing unit, comprising: a helical throttle channel for reducing the pressure of a fluid, in particular a liquid, the helical throttle channel having a plurality of Has windings that are connected to each other in a vibration-damping manner. The vibration-damping connection increases the inherent rigidity of the helical throttle channel.

As described above, a throttle channel with a comparatively long length is required for a pressure reducing unit. The length of the throttle channel depends on the diameter of the throttle channel (typically between 2 mm and 10 mm) and on the local flow velocity. Typically, to generate a pressure loss in the range between approx. 20-250 mbar, a length of the throttle channel (in the unrolled state) between approx. 50 mm and approx. 2000 mm is required. For higher pressure loss values to be achieved, the (unfolded) length of the throttle channel (at the same diameter and at the same flow velocity) scales linearly upwards. In the case of a throttle channel that is designed as a pipeline, the comparatively long length leads to a low (bending) rigidity, even if it is designed to be helical in order to reduce the required installation space, which leads to flow-induced when the fluid flows through the throttle channel leads to vibrations.

The vibration-damping connection of the plurality of turns to one another serves to limit the ability of the individual turns to move relative to one another. The vibration-damping connection between the windings can be designed to be rigid, so that the windings of the throttle channel are fixed in their position relative to one another. However, it is also possible for the windings to be connected via a vibration-damping material that allows a (damped) movement or change in position of the windings of the throttle channel relative to one another. In both cases, the vibration-damping connection of the turns of the helical throttle channel can increase the inherent rigidity of the throttle channel and reduce flow-induced vibrations. In one embodiment, the helical throttle channel is designed as a helical pipeline with a plurality of pipe turns. The material of the pipeline can be a stainless material, for example steel. In the event that the throttle channel is designed as a helical pipeline, it is advantageous to connect the pipe turns to one another on their outer sides and, if necessary, to fix them to one another during the connection in order to reduce flow-induced vibrations.

In the case of a pressure reducing unit with a single helical throttle channel in the form of a free steel pipeline, it was observed that the flow-induced vibrations when the fluid flows through the pipeline generate low natural frequencies, i.e. the helical pipeline is set in vibration at the corresponding frequencies. However, low natural frequencies are usually in a frequency range that is unfavorable for the position control of the mirrors in a projection optics of an EUV lithography system (see above) and can generate overlay and wavefront errors in terms of structural dynamics.

It is possible to design the connection of the pipe turns (on their outer sides) so that the natural frequencies of the helical pipe lie in a desired frequency range. In particular, the inherent rigidity of the helical pipeline can be designed such that the natural frequencies of the helical pipeline are at higher natural frequencies and therefore no longer overlap with the frequency range of the position control of the mirrors.

There are various options for the type of connection of the pipe turns. One possibility is to connect adjacent pipe turns on their outsides in a materially bonded manner, for example weld. In this case, adjacent pipe turns lie practically directly against one another on their outsides.

In a further development, the pipe turns are preferably rigidly connected to one another on their outer sides via at least one stiffening element. In this case, adjacent pipe turns do not generally lie directly against one another on their outer sides, but are connected to one another indirectly via the stiffening element. The stiffening element can be, for example, a rod, a sleeve or the like extending in the longitudinal direction of the pipeline, with which the pipe windings are connected on their outer sides (at points or flatly), for example via a material connection.

A stiffening element in the form of a clamp or the like, which surrounds the two outermost pipe turns of the helical pipe in the longitudinal direction, is also possible in principle. The length of the clamp can be chosen so that adjacent pipe turns rest against each other with their outer sides. It is therefore not absolutely necessary that the pipe turns are connected to the stiffening element on their outer sides via a cohesive connection; rather, another type of connection, for example a clamping connection, is also possible.

In a further development, the pipe turns are embedded, in particular cast, in a vibration-damping body. As described above, the material of the helical pipeline is usually steel or another stainless material. The vibration-damping body typically has a material that does not match the material of the helical pipe. The material of the vibration-damping body can be, for example, an elastomer, but this is not absolutely necessary. By embedding the pipe turns in the Material of the vibration-damping body can effectively reduce flow-induced vibrations. The pipe turns can be embedded by pouring them into the material of the flow-damping body, but it is also possible to embed or encase the pipe turns in another way, for example using an additive process.

The material of the vibration-damping body is preferably a resin or a fluoroelastomer, in particular Viton. Pouring the pipe turns of the helical pipe into a resin can be accomplished in a particularly simple manner. The use of fluoroelastomers, especially from Viton, as a material for the vibration-damping body has proven to be beneficial, as this material is approved for use in EUV lithography systems.

In an alternative embodiment, the helical throttle channel is designed as a helical cavity in a preferably one-piece base body. In this embodiment, the throttle channel is not designed in the form of a pipeline, but rather forms a cavity in the base body through which a fluid can flow. The material of the base body can be, for example, steel or another stainless material that does not degrade when the fluid, typically water, flows through it. The helical cavity can be produced in the base body in different ways, for example by laser ablation or by conventional material-removing processes. It is also possible to use a model of the helical throttle channel, which is poured over with the melt in a casting process when producing the base body and burns in the process (so-called “lost shape”). By burning the model, the helical cavity is formed in the base body. In a further development of this embodiment, the base body is produced using an additive manufacturing process, for example using a 3D printing process. The base body can basically be printed or manufactured from all weldable materials. The material of the base body is preferably a stainless material, for example stainless steel. The pressure reducing unit can consist of the (ideally one-piece) base body in which the helical cavity is formed. However, it is also possible for the pressure reducing unit to have, in addition to the base body, further components that are connected to the base body, for example with an inlet opening or an outlet opening of the helical cavity. The components can be, for example, a nozzle channel or a diffuser channel (see below).

In a further embodiment, the helical throttle channel has a constant flow cross section. To reduce pressure through viscous friction, it is beneficial if the flow cross section in the throttle channel is constant. The pressure loss App due to friction in a circular flow channel with a length L and a diameter D is:

Ap _R = X ( L ^/ D ) (p / 2 ) v ² , (1 ) where m/s). The helical throttle channel preferably has a constant pitch or gradient.

In a further embodiment, the pressure reducing unit has a nozzle channel with a decreasing flow cross section for supplying the fluid to the helical throttle channel. As can be seen from the above given equation (1), the pressure loss depends on the square of the flow velocity v of the fluid and increases with increasing flow velocity. It is therefore advantageous if the fluid in the throttle channel has the greatest possible flow velocity v, which can be achieved by reducing the flow cross section in the nozzle channel. The nozzle channel generally connects directly to the helical throttle channel at the end that has the minimum flow cross section.

In a further embodiment, the pressure reducing unit comprises a diffuser channel with an increasing flow cross section for removing the fluid from the helical throttle channel. In the diffuser channel, the flow velocity of the fluid is reduced by the increase in the flow cross section starting from the helical throttle channel. As a rule, the diffuser channel is only required if the flow velocity of the fluid in the nozzle channel has been increased in order to reduce the flow velocity of the fluid back to the value before entering the pressure reducing unit.

In a further embodiment, the flow cross section of the nozzle channel decreases at an angle of 15° or less and/or the flow cross section of the diffuser channel increases at an angle of 3.5° or less. The values given here refer to the angle between the wall of the nozzle channel or the diffuser channel to the central axis. These angles therefore correspond to half the opening angle of the nozzle channel or the diffuser channel.

It has proven to be advantageous if the change in the flow cross section in the nozzle channel and in the diffuser channel per unit length is not chosen to be too large in order to generate as few flow-induced vibrations as possible. At larger angles you can the pressure conditions in the flow boundary layers lead to flow separations and, as a result, to vortices and turbulence. In a diffuser channel in which the flow cross section increases, flow separation can occur at smaller angles than in a nozzle channel, since the flow is forced to separate with difficulty due to the decreasing flow cross section of the nozzle channel. The flow cross section of the nozzle channel, the diffuser channel and the helical throttle channel is preferably circular, but can in principle also have a different geometry.

In a further embodiment, the pressure reducing unit is designed in one piece. The pressure reducing unit, which can in particular have the nozzle channel, the helical throttle channel and the diffuser channel, is preferably designed in one piece. Such a one-piece design of the pressure reducing unit is favorable, but not absolutely necessary: It is possible, for example, for the nozzle channel and/or the diffuser channel to form two separate components which are connected in a fluid-tight manner to a respective end of the helical throttle channel. The nozzle channel and the diffuser channel generally run in a straight line, but may also have a curvature and may be helical like the throttle channel. Due to the comparatively short length of the nozzle channel and the diffuser channel, only minor flow-induced vibrations are generally generated there.

The pressure reducing unit can - with the exception of the right or left hand movement of the helical throttle channel - be designed symmetrically with respect to the flow direction of the fluid, that is, if the flow direction of the fluid is reversed, the roles of the nozzle channel and the diffuser channel are swapped without this having any effect on the pressure reduction of the fluid. As described above, the opening angle of the nozzle channel and the opening angle of the Diffuser channel can be selected differently. In this case, the pressure reducing unit is designed asymmetrically with respect to the flow direction of the fluid. In this case, the opening angle of the nozzle channel is larger than the opening angle of the diffuser channel. Due to the larger opening angle, the length of the nozzle channel can be shortened compared to the length of the diffuser channel. This is particularly advantageous if the installation space is limited.

A further aspect of the invention relates to an EUV lithography system, comprising: at least one component through which a fluid can flow, in particular an optical element, a structural component or a fluid line, wherein the component through which the fluid can flow has at least one pressure reducing unit, which is designed as described above is. The EUV lithography system can be an EUV lithography system for exposing a wafer or another optical arrangement that uses EUV radiation, for example an EUV inspection system, for example for inspecting masks used in EUV lithography, wafers or the like.

The optical element through which the fluid can flow can be, for example, a directly cooled mirror that has a substrate into which cavities or cooling channels are introduced, through which a fluid, typically water, flows to cool the mirror. However, it can also be another optical element, for example a lens. The structural component can be, for example, a holder, for example a frame for holding optical elements, a frame for holding sensors or a support frame, as used in EUV lithography systems, especially in EUV lithography systems . The materials of these structural components, which can be aluminum, steel, ceramics, etc., often contain channels through which a fluid can flow introduced to cool them. The fluid line can be, for example, a pipeline of a fluid line system, in particular a cooling system or a cooling circuit. The pipeline can be used, for example, to supply a cooling fluid to an optical element, a structural component or another type of component.

As described above, with the help of the pressure reducing unit according to the invention, the structural dynamic natural frequencies can be adjusted or optimized independently of the pressure loss, without having to increase the required installation space. In this way, a local reduction in the disturbance input to the respective pressure reducing unit caused by structural dynamic behavior can be achieved.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, based on the figures in the drawing, which show details essential to the invention, and from the claims. The individual features can be implemented individually or in groups in any combination in a variant of the invention.

drawing

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

1 shows a schematic meridional section of a projection exposure system for EUV projection lithography,

2a is a schematic representation of a pressure reducing unit with a throttle channel in the form of a helical pipeline, whose pipe turns are rigidly connected to one another via a rod-shaped stiffening element,

Fig. 2b is a schematic representation analogous to Fig. 2a, in which the pipe turns are embedded in a vibration-damping body, as well

Fig. 2c is a schematic representation analogous to Fig. 2a, b, in which the throttle channel forms a helical cavity in a cylindrical base body.

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

Below, with reference to FIG. 1, the essential components of an optical arrangement for EUV lithography in the form of a projection exposure system 1 for microlithography are described as an example. The description of the basic structure of the projection exposure system 1 and its components is not to be understood as restrictive.

One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, lighting optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the other lighting 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. A Cartesian xyz coordinate system is shown in FIG. 1 for explanation purposes. The x direction runs perpendicular to the drawing plane. The y-direction is horizontal and the z-direction is vertical. The scanning direction in FIG. 1 runs 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 into 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 area 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, on the one hand, of the reticle 7 via the reticle displacement drive 9 and, on the other hand, of the wafer 13 via the wafer displacement drive 15 can be carried out synchronously with one another.

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 in particular 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) or a DPP source. Source (Gas Discharged Produced Plasma, plasma produced by gas discharge). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL). The illumination radiation 16, which emanates 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 hyperboloid 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, Gl), i.e. with angles of incidence greater than 45°, or in normal incidence (Normal Incidence, NI), i.e. with angles of incidence smaller 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 false 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, having the radiation source 3 and the collector mirror 17, and the illumination optics 4.

The lighting optics 4 comprises a deflection mirror 19 and, downstream of it in the beam path, a first facet mirror 20. The deflection mirror 19 can be a flat 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 false light of a wavelength that deviates from this. The first facet mirror 20 includes a large number of individual first facets 21, which are also referred to below as field facets. Some of these facets 21 are shown in FIG. 1 only as examples. In the beam path of the lighting optics 4 there is a downstream of the first facet mirror 20 second facet mirror 22. The second facet mirror 22 comprises a plurality of second facets 23.

The lighting optics 4 thus forms a double faceted system. This basic principle is also known as the honeycomb condenser (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 actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5.

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

In the example shown in FIG. 1, the projection system 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi (i=1, 2, ...) 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 double-obscured optic. The projection optics 10 has an image-side numerical aperture that is larger than 0.4 or 0.5 and which can also be larger than 0.6 and which can be, for example, 0.7 or 0.75.

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

The projection exposure system 1 has one or more cooling circuits in order to flow a fluid in the form of a cooling liquid, typically water, through the mirrors Mi of the projection system 10 and other components, for example structural components such as support frames or the like. For this purpose, in the mirrors Mi, more precisely in their substrates, Hollow structures are introduced through which the coolant flows. In order to balance the flow of the cooling liquid through parallel cooling channels or hollow structures of the mirror Mi and other components of the projection exposure system 1, for example the structural components described above, pressure reducing units are used, which are in fluid lines of the cooling circuit or the cooling system of the projection exposure system 1 or if necessary . be integrated into the mirror Mi or into the respective structural components. Three examples of such a pressure reducing unit 25 are shown schematically in FIGS. 2a-c and are described below.

The pressure reducing unit 25 shown in FIG. 2a has a helical throttle channel, which is designed as a helical pipeline 26a in the form of a steel pipe. In the example shown, the helical pipe 26a has a number of fourteen pipe turns 27. It goes without saying that the helical pipe 26a can also have more or fewer pipe turns 27. The helical pipe 26a is used to reduce the pressure of a fluid F in the form of a liquid, which is indicated by an arrow in FIG. 2a.

In the example shown in FIG. 2a, the helical pipe 26a forms a middle section of a one-piece pipe 26, which, in addition to the helical pipe 26a, has two further sections in the form of a nozzle channel 26b and a diffuser channel 26c. The nozzle channel 26b has a free end with an inlet opening 28a for the fluid F and merges into the helical pipe 26a at its other end. The diffuser channel 26c starts from the left end of the helical pipe 26a in FIG. The flow cross section AK or the diameter of the rectilinear nozzle channel 26b decreases starting from the inlet opening 28a in its longitudinal direction or along its central axis 29. At the transition from the nozzle channel 26b to the helical pipeline 26a, the flow cross section AK of the nozzle channel 26b is minimal. By reducing the flow cross section AK, the speed of the fluid F as it enters the helical pipe 26a is increased, which promotes the reduction of the pressure of the fluid F in the helical pipe 26a through viscous friction.

The helical pipeline 26a has a constant flow cross section AD. A constant flow cross section AD is favorable for generating the pressure loss of the fluid F through viscous friction without changing the speed of the fluid F. The rectilinear diffuser channel 26c has a flow cross section AE which increases continuously in the longitudinal direction or along its central axis 30. In the example shown, the nozzle channel 26b and the diffuser channel 26c are identical in construction, i.e. they have the same geometry and the same dimensions and are arranged mirror-symmetrically with respect to a central plane of the helical pipe 26. At the inlet opening 28a and at the outlet opening 28b of the pressure reducing unit 25, the flow cross section is the same size (i.e. the following applies: AK = AE).

As can also be seen in FIG. 2a, the channel wall of the nozzle channel 26b in the example shown is conical, ie it is aligned at a constant angle ai with respect to the central axis 29 of the nozzle channel 26b. Correspondingly, the conical channel wall of the diffuser channel 26c is aligned at a constant angle 02 with respect to the central axis 30 of the diffuser channel 26c. The angle ai with respect to the central axis 29 of the nozzle channel 26b is approximately 3.5° in the example shown, But it can also be chosen larger, but it should not be larger than approx. 15°. The angle 02 with respect to the central axis 30 of the diffuser channel 26c is also approximately 3.5° in the example shown and should not be chosen larger in order to prevent turbulence when the fluid F flows through. It is understood that the nozzle channel 26b and the diffuser channel 26c do not necessarily have to have conical channel walls with a constant angle ai, 02 with respect to the respective central axis 29, 30, rather the angle ai, 02 can be over the length of the nozzle channel 26b and/or or the diffuser channel 26c vary. In particular, the angle ai of the nozzle channel 26b can be larger than the angle O2 of the diffuser channel 26c.

In the example shown, the pipe 26 is made of stainless steel and, in particular in the section with the helical pipe 26a, has a low bending stiffness, which can lead to flow-induced vibrations when the fluid F flows through, which, among other things, has a disadvantageous effect on the position control of the mirror Mi the projection optics 10 can affect.

In order to increase the bending stiffness of the helical pipe 26a, in the example shown in FIG. 2a, the pipe turns 27 of the helical pipe 26a are rigidly connected to a stiffening element 31 on their outer sides 27a. In the example shown, the connecting element 31 is a rod which extends over the entire length of the helical pipe 26a. The pipe turns 27 are welded on their outer sides 27a to the rod-shaped connecting element 31, which in the example shown is also made of steel. It goes without saying that the connection between the rod-shaped connecting element 31 and the outer sides 27a of the respective pipe turns 27 can also take place in another way, for example via an adhesive connection. By connecting the pipe turns 27 by means of the rod-shaped connecting element 31, the pipe turns 27 can carry out no or only slight movements relative to one another, so that Flow-induced vibrations of the helical pipeline 26a can be reduced. In principle, it is also possible to connect one or more stiffening elements 31 to the outer sides 27a of the pipe turns 27 via a clamping connection in order to ideally connect them rigidly to one another.

Fig. 2b shows an example of a pressure reducing unit 25, which has a continuous, one-piece tube 26, which is designed as described in Fig. 2a. To increase the inherent rigidity or to dampen vibrations, the pipe turns 27 of the helical pipe 26a in FIG this cools down.

In the example shown, the vibration-damping body 32 consists of an elastomer, more precisely a fluoroelastomer (Viton). However, it goes without saying that the vibration-damping body 32 can also be made from another material that is suitable for damping the relative movement of the pipe turns 27 to one another. The material can be, for example, a resin. The resin can be an elastomer, but it is also possible that the material in which the pipe turns 27 are embedded is a rigid material that practically completely prevents relative movement of the pipe turns 27. It goes without saying that the vibration-damping body 32 in FIG. 2b is shown as cylindrical only by way of example and can also have a different geometry.

Fig. 2c shows a further example of a pressure reducing unit 25, in which the helical throttle channel is in the form of a helical cavity 26a 'shown in dashed lines in Fig. 2c in a cylindrical base body 33 is trained. The cylindrical base body 33 consists of a weldable material, more precisely steel, and was manufactured using an additive manufacturing process using 3D printing. During 3D printing, the base body 33 in the example shown was produced in layers from a powder bed, with the helical cavity 26a' being left out when the base body 33 was constructed in layers. The helical cavity 26a' forms the negative impression of the inside of the helical pipe 26a described in FIGS. 2a, b. Alternatively, the cavity in the base body 33 can be created, for example, by laser ablation. It is also possible to pour a melt made from the material of the base body 33 over a model of the helical cavity 26a ', whereby the model burns (so-called "lost form"). After the model has been burned, the helical cavity 26a' remains in the base body 33.

The pressure reducing unit 25 shown in FIG. 2c, like the pressure reducing units 25 shown in FIGS. 2a, b, has a nozzle channel 26b and a diffuser channel 26c, which are formed in one piece with the base body 33. The entire pressure reducing unit 25 was produced by 3D printing in the example shown in FIG. 2c. It goes without saying that, alternatively, the nozzle channel 26b and the diffuser channel 26c can be manufactured as separate components which are connected in a fluid-tight manner to the helical cavity 26a' on a respective end face of the base body 33.

Through the vibration-damping, possibly rigid connection of the windings 27 of the helical throttle channel 26a, 26a' to one another, flow-induced vibrations can be reduced. In particular, the frequencies of the natural oscillations of the pressure reducing unit 25 can be adjusted or shifted into a frequency range that does not overlap with the frequency range of the position control of the mirrors Mi of the projection optics 10.

Claims

Claims Pressure reducing unit (25), comprising: a helical throttle channel (26a, 26a') for reducing the pressure of a liquid (F), the helical throttle channel (26a, 26a') having a plurality of turns (27) which are connected to one another in a vibration-damping manner. Pressure reducing unit according to claim 1, in which the helical throttle channel is designed as a helical pipeline (26a) with a plurality of pipe turns (27). Pressure reducing unit according to claim 2, in which the pipe turns (27) are preferably rigidly connected to one another on their outer sides (27a) via at least one stiffening element (31). Pressure reducing unit according to claim 2, in which the pipe windings (27) are embedded, in particular cast, in a vibration-damping body (32). A pressure reducing unit according to claim 4, wherein said vibration damping body (32) is formed of a resin or a fluoroelastomer. Pressure reducing unit according to claim 1, in which the helical throttle channel (26a') is designed as a helical cavity in a preferably one-piece base body (33). Pressure reducing unit according to claim 6, in which the base body (33) is produced by additive manufacturing. Pressure reducing unit according to one of the preceding claims, in which the helical throttle channel (26a, 26a') has a constant flow cross section (AD). Pressure reducing unit according to one of the preceding claims, further comprising: a nozzle channel (26b) with a decreasing flow cross section (AK) for supplying the liquid (F) to the helical throttle channel (26a, 26a'). Pressure reducing unit according to one of the preceding claims, further comprising: a diffuser channel (26c) with an increasing flow cross section (AE) for discharging the liquid (F) from the helical throttle channel (26a, 26a '). Pressure reducing unit according to one of claims 9 or 10, in which the flow cross section (AK) of the nozzle channel (26b) decreases with an angle (ai) of 15° or less and/or in which the flow cross section (AE) of the diffuser channel (26c) with a Angle (02) increases by 3.5° or less. Pressure reducing unit according to one of the preceding claims, which is designed in one piece. EUV lithography system (1), comprising: at least one component through which a liquid (F) can flow, in particular an optical element (Mi) or a structural component, wherein the component through which the liquid (F) can flow at least one pressure reducing unit (25) according to one of has previous claims.