Method for reducing acoustic vibrations, connection element, and projection exposure system

Abstract

The invention relates to a method for reducing acoustic vibrations in a connection element (30, 50, 70), wherein the connection element (30, 50, 70) connects two components of a projection exposure system to one another, and the connection element (30, 50, 70) is filled with a fluid (34), the method comprising the following method steps: - determining acoustic vibrations expected in the connection element (30, 50, 70); - configuring the connection element (30, 50, 70) to at least partially reduce the acoustic vibrations expected in the connection element (30, 50, 70); - determining an acoustic transfer function (37) of the configured connection element (30, 50, 70); - comparing the achieved reduction with a predetermined specification based on the transfer function (37); - repeating the configuration of the connection element (30, 50, 70) and the subsequent method steps until the specification is satisfied. The invention also relates to a connection element (30, 50, 70) for connecting two components of a projection exposure system (1, 101), wherein the connection element (30, 50, 70) is filled with a fluid (34) and is characterised in that the connection element (30, 50, 70) comprises at least one vibration-reducing portion (40, 40.1, 60, 80, 90). The invention also relates to a projection exposure system (1, 101) comprising a connection element (30, 50, 70) according to any one of the described embodiments.

Description

[0001] Method for reducing acoustic vibrations, connecting element and projection exposure system This application claims the priority of German patent application DE 102024 202075.3, filed on March 6, 2024, the content of which is incorporated herein by reference in its entirety. The invention relates to a method for reducing acoustic vibrations, a connecting element for a projection exposure system and a projection exposure system with such a connecting element. Projection exposure systems for semiconductor lithography are used to produce extremely fine structures, in particular on semiconductor components or other microstructured components.The operating principle of these systems is based on creating extremely fine structures down to the nanometer range by means of a generally reduced-size image of structures on a mask, a so-called reticle, on an element to be structured, such as a wafer, which is provided with photosensitive material. The minimum dimensions of the created structures depend directly on the wavelength of the light used. The light sources used have wavelengths from 100 nm to 300 nm in an emission wavelength range known as the DUV range. Recently, light sources with an emission wavelength in the range of a few nanometers, for example, between 1 nm and 120 nm, particularly in the range of 13.5 nm, have been increasingly used. This emission wavelength range is also referred to as the EUV range.To illuminate the structures and in particular to image them, optical elements such as lenses, but especially in the EUV range also mirrors, are used. Their so-called optical effective surfaces are exposed to light, the so-called useful light, during normal operation of the associated system for imaging and exposure. These projection exposure systems have temperature control systems for the thermal stabilization of optical elements, components, structures, and the entire projection exposure system. The temperature control systems comprise temperature control lines and temperature control channels. While the temperature control channels are formed in optical elements, in particular mirrors, components, and structural parts, the temperature control lines connect the temperature control channels to a water cabinet designed for supply and treatment, or connect the temperature control channels to each other.As a rule, the temperature control lines, referred to below as lines, are attached to the structures of the system itself. The lines are usually designed as tubes, but can also include more flexible hoses or bellows. Active temperature control ensures both the highest possible heat dissipation or heat supply and good controllability of the system, which is ensured in particular by a minimal delay in the temperature control system. Due to its high heat capacity and availability, ultrapure water is usually used as the temperature control fluid; however, other industrially common cooling fluids can also be used. The flowing fluid ensures improved heat transfer at the surfaces through which the flow occurs (forced convection).Especially in the context of the development of temperature-controlled optical elements and their infrastructure, pressure fluctuations / pulsations transported and transmitted via the fluid (here, water) play a crucial role in the performance of the projection exposure system and the imaging quality of the structures on the wafer. The associated pressure waves are longitudinal waves and propagate at the speed of sound in the fluid, for example, in sound-hard environments such as stainless steel pipes, at approximately 1500 m / s. These vibrations transmitted via the fluid are referred to as acoustic vibrations due to their transmission via pressure waves.The cause of acoustic vibrations can be so-called fluid-induced vibrations, which, depending on local geometric boundary conditions and the boundary conditions during the inflow and outflow, are caused by persistent periodic and random fluctuations in the flow, also known as turbulence. These hydrodynamic fluctuations lead to the coupling of acoustic pressure waves, which propagate as acoustic vibrations both downstream and upstream and, depending on the geometry of the cooling circuit, can lead to standing waves, such as those found in organ pipes. Furthermore, acoustic vibrations can be transmitted vibrations, which originate from mechanical vibrations of the structural mechanics—i.e., pipes, structures, components, and all other mechanical components directly or indirectly connected to the fluid—which are transmitted to the fluid.Acoustic and mechanical vibrations are connected or coupled to each other via the pipes / lines and can merge in both directions. A coupling element must be present from the fluid to the structural mechanics, which can convert the acoustic vibrations, formed as longitudinal waves, into a force acting on the structural mechanics. The acoustic vibrations in the fluid and the resulting forces on the inner surfaces of the temperature control lines and channels lead to a frequency-dependent dynamic excitation of the temperature-controlled optical elements, components, structures, and thus almost the entire projection exposure system. The sensitivities of the components of the optical system to acoustic or mechanical vibrations also play a role.In general, the acoustic vibrations are reflected differently in the temperature control system depending on the geometric and acoustic boundary conditions as well as the materials used, resulting in frequency-dependent force amplitudes that affect the structural mechanics. These vibrations have a negative impact on the system performance of the projection exposure system, for example, in the form of critical frequencies that negatively influence the position control of the optical elements or through deformation of the optical active surfaces of the optical elements due to pressure pulsations in the temperature control channels. The described effects can negatively influence the image quality of the projection exposure system. The object of the present invention is to provide a method for the improved reduction of acoustic vibrations.A further object of the invention is to provide a fluid-filled connecting element of a projection exposure system for reducing acoustic vibrations. This object is achieved by a method and a connecting element having the features of the independent claims. The subclaims relate to advantageous developments and variants of the invention. A method according to the invention for reducing acoustic vibrations in a connecting element, wherein the connecting element connects two components of a projection exposure system and the connecting element is filled with a fluid, comprises the following method steps: - Determining acoustic vibrations expected in the connecting element. - Designing the connecting element to at least partially reduce the acoustic vibrations expected in the connecting element. - Determining an acoustic transfer function of the designed connecting element.- Comparison of the achieved reduction in acoustic vibrations with a predefined specification based on the transfer function. - Repeating the design of the connecting element and the following process steps until the specification is met. The process enables adaptation of the connecting element to reduce acoustic vibrations, i.e. vibrations transmitted via the fluid. In particular, the acoustic vibrations can be determined with frequency resolution. The acoustic vibrations can generally be determined at one location on the connecting element or in the form of a transfer function from one location to another on the connecting element. The transfer function has the advantage that the resonance frequency of the connecting element or the resonance frequency relevant for reducing the acoustic vibrations is determined.a section of the connecting element and the frequency ranges in which the acoustic vibrations are reduced, i.e. transmitted by the connecting element with a factor of less than 1, can be read directly. In a first embodiment, the connecting element can be designed such that at least a section of the connecting element is excited in its resonance by the determined vibrations. The section is also referred to below as a resonator. The resonator is preferably designed such that a frequency with a pronounced amplitude and / or a frequency critical for a subsequent component is dampened by the resonator. This can, for example, be a critical frequency for the stability of a position control of an optical element. In particular, an oscillation of the resonator caused by the resonator can cause a change in volume, in particular of elastic components orComponents with a higher degree of compliance than the rest of the piping system (e.g., made of steel) within the connecting element cause this. The volume change causes a change in the acoustic impedance, i.e., the relationship between pressure and flow of the fluid in the connecting element, and thus a phase shift between pressure and flow. In the case of ideal resonance, the resonator, i.e., a part of the structural mechanics, oscillates so phase-shifted relative to the acoustic oscillation propagating in the fluid in the form of a longitudinal wave that the mechanical oscillations of the resonator and the acoustic oscillations in the fluid cancel each other out, or at least almost cancel each other out. Acoustic oscillations with a frequency matching the resonance frequency are therefore not transmitted through the connecting element, or are transmitted only with significant damping.In the further course of a fluid line system of the projection exposure system, the acoustic vibrations of this frequency may have no or only a negligible influence on the image quality. In a further embodiment, the design of the connecting element may include an adjustment of the stiffness of an elastic element encompassed by the section. The elastic elements of the resonator, which are predominantly designed as metallic bellows, can be adjusted by adjusting the material thickness and / or the geometry of the bellows and thereby influence the oscillatory system of the resonator. Furthermore, the design may include an adjustment of the mass of the section. The mass of the resonator can be adjusted in particular by means of additional masses detachably or permanently connected to components of the section.This is particularly interesting for adjusting the resonance frequency after assembly of the connecting element, when adjusting the stiffness of the bellows is no longer possible or only possible with increased effort. Alternatively, the design of the connecting element (30, 50, 70) can be based on sensitive frequency ranges of the component to at least partially reduce the acoustic vibrations expected in the connecting element (30, 50, 70). These can, for example, be frequency ranges in which the components themselves have a natural frequency. This frequency or frequency range does not necessarily have to correspond to or include the maximum of the acoustic vibration itself. Furthermore, the design of the connecting element (30, 50, 70) can be based on the effects on the imaging quality of the projection exposure system to at least partially reduce the acoustic vibrations expected in the connecting element (30, 50, 70).In this case, the mechanical disturbances generated by the acoustic vibrations on a subsequent component are multiplied by the optical sensitivities of the optical elements mounted in the component. The optical disturbance thus caused can, for example, have less impact on the image quality if the component is excited in the direction of the beam path of the electromagnetic radiation used to image the masks than if the component is excited perpendicular to the beam path. Thus, the frequencies of the acoustic vibrations that have the greatest negative impact on the image quality are attenuated. This frequency or frequency range also does not necessarily have to correspond to or encompass the maximum of the acoustic vibration itself.A fluid-filled connecting element according to the invention for connecting two components of a projection exposure system is characterized in that the connecting element comprises at least one vibration-reducing section. The vibration-reducing section is suitable for reducing acoustic vibrations in the fluid. In a first embodiment, the section of the connecting element can be designed as an oscillatory system. With suitable excitation, this system can be excited at its natural frequency and, in combination with a volume change, act as a resonator. In particular, the section can have a coupling element. A coupling element couples the structural mechanics—i.e., tubes, bellows, and mechanical components of the connecting element—with the fluid in the connecting element in such a way that an acoustic vibration transported in the fluid causes a force on the structural mechanics.In a first embodiment, the coupling element can be designed as a bend. The fluid presses against the inner surfaces of the connecting element with constant pressure (or, at frequencies > 0 Hz, with frequency-dependent pressure amplitudes). Due to the different sizes of the inner and outer radius surfaces in the bend, a differential force is generated at the bend, thus transferring the energy of the acoustic vibration to the structural mechanics. The acoustic vibrations, which usually propagate as longitudinal waves through the connecting element, thus excite the structural mechanics, in particular the resonator. Furthermore, the coupling element can have a cross-sectional change. The acoustic vibration thus causes a force on the structural mechanics through the resulting impedance jump or the associated pressure change.The cross-sectional change in the coupling element can, for example, be conical or stepped and implemented in a pipe section or at the transition to a bellows. In a further embodiment, the section can have an interface for connecting additional masses. The additional masses serve to adjust the resonance of the resonator and can, in particular, be replaced while the system is already assembled. In a further embodiment, the section can have an element for changing the volume. This can be implemented, for example, as a bellows, but in principle also as a (visco-)elastic hose section or as a radially at least partially (visco-)elastic coupling element. In particular, the resonance of the section, which corresponds to a resonator, can cause a reduction in the amplitude of the acoustic oscillation at the resonant frequency of the resonator.In the case of known or at least approximately known acoustic vibrations or acoustic vibration sources in the fluid, the connecting element can be designed such that at least some of the acoustic vibrations can also be reduced. Acoustic vibrations from a known source itself can be reduced, particularly in the range of the highest amplitudes. It is also possible to first determine the sensitive frequency ranges of the overall system with regard to acoustic vibrations and then reduce the vibrations preferably in those frequency ranges, as explained above. This maximum does not necessarily have to be the maximum of the acoustic excitation itself. Furthermore, it is also possible to reduce the acoustic vibrations preferably in those frequency ranges that have a negative impact on the image quality of the projection exposure system, as explained above.Furthermore, the connecting element can be designed to decouple the transmission of mechanical vibrations via the structural mechanics. With a suitable design, the connecting element can be designed both to decouple mechanical vibrations and to dampen acoustic vibrations, so that no additional measures for damping acoustic vibrations are necessary. This can advantageously have a positive effect on manufacturing costs and reduce the complexity of the system. In a further embodiment, the connecting element can comprise a damping element. This can be arranged at a connection between the connecting element and the structure and dampen bearing forces caused by the resonator occurring at the connection. This has the advantage that part of the energy of the acoustic vibrations is dissipated by the damping element and converted into heat.Suitable damping elements include, in particular, tuned mass dampers, vibration absorbers, and shunt damping mechanisms, i.e., electrical networks for vibration damping using piezoelectric sensors / actuators. A projection exposure system according to the invention has a connecting element according to one of the preceding embodiments. Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing.Figure 1 shows a meridional section through a projection exposure system for EUV projection lithography. Figure 2 shows a meridional section through a projection exposure system for DUV projection lithography. Figure 3 shows a first embodiment of a connecting element according to the invention. Figure 4 shows a diagram of an acoustic transfer function of a connecting element to explain the mode of operation. Figures 5a, b show a detail of the invention. Figures 6a, b show further embodiments of connecting elements. Figure 7 shows a damping device. Figure 8 shows a flowchart of a possible method for designing a connecting element. The following describes, by way of example, the essential components of a projection exposure system 1 for microlithography with reference to Figure 1. The description of the basic structure of the projection exposure system 1 and its components is not intended to be limiting.One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a 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 illumination 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 Figure 1 for illustrative purposes. The x-direction runs perpendicular to the drawing plane. The y-direction runs horizontally, and the z-direction runs vertically. The scanning direction in Figure 1 runs along the y-direction. The z-direction runs perpendicular to the object plane 6.The projection exposure system 1 comprises projection optics 10. The projection optics 10 serve to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular along the y-direction, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and of the wafer 13, on the other hand, via the wafer displacement drive 15 can be synchronized with one another. Radiation source 3 is an EUV radiation source.The radiation source 3 emits in particular EUV radiation 16, which is also referred to below as useful radiation, illumination radiation or illumination light. The useful radiation has in particular a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example an LPP source (laser produced plasma) or a DPP source (gas discharged produced plasma). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free-electron laser (FEL). The illumination radiation 16 emanating from the radiation source 3 is bundled by a collector 17. The collector 17 may be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces.The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 at grazing incidence (GI), i.e., at angles of incidence greater than 45° relative to the normal direction of the mirror surface, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector 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 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the radiation source 3 and the collector 17, and the illumination optics 4. The illumination optics 4 comprise a deflection mirror 19 and, downstream of the deflection mirror in the beam path, a first facet mirror 20.The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, which are also referred to below as field facets. Only a few of these facets 21 are shown in Fig. 1 as examples.The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partially circular edge contour. The first facets 21 can be designed as flat facets or, alternatively, as convexly or concavely curved facets. As is known, for example, from DE 102008009600 A1, the first facets 21 themselves can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can, in particular, be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 102008009600 A1. Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e., along the y-direction. In the beam path of the illumination optics 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20.If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1614008 B1, and US 6,573,978. The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets. The second facets 23 may also be macroscopic facets, which may, for example, be round, rectangular or hexagonal in shape, or alternatively facets composed of micromirrors.In this regard, reference is also made to DE 102008009600 A1. The second facets 23 can have flat or, alternatively, convex or concave curved reflection surfaces. The illumination optics 4 thus forms a double-faceted system. This basic principle is also referred to as a honeycomb condenser (fly's eye integrator). It can be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the pupil facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 102017220586 A1. With the aid 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 bundle-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5. In a further embodiment of the illumination optics 4 (not shown), a transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which transmission optics contributes in particular to the imaging of the first facets 21 in the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GI mirrors, gracing incidence mirrors). The illumination optics 4 has, in the embodiment shown in Fig.1, after the collector 17 there are exactly three mirrors, namely the deflecting mirror 19, the field facet mirror 20 and the pupil facet mirror 22. In a further embodiment of the illumination optics 4, the deflecting mirror 19 can also be omitted, so that the illumination optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22. The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optics into the object plane 6 is generally only an approximate imaging. The projection optics 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1. In the example shown in Figure 1, the projection optics 10 comprises six mirrors M1 to M6.Alternatives with four, eight, ten, twelve or a different 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 optics 10 are doubly obscured optics. The projection optics 10 have a numerical aperture on the image side that is greater than 0.5 and can also be greater than 0.6 and can be, for example, 0.7 or 0.75. Reflection surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. The mirrors Mi, just like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16.These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon. The projection optics 10 have a large object-image offset in the y-direction between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction can be approximately as large as a z-distance between the object plane 6 and the image plane 12. The projection optics 10 can, in particular, be anamorphic. In particular, it has different image scales βx, βy in the x- and y-directions. The two magnifications βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive magnification β means an image without image inversion. A negative sign for the magnification β means an image with image inversion.The projection optics 10 thus results in a reduction in the ratio 4:1 in the x-direction, i.e., in the direction perpendicular to the scanning direction. The projection optics 10 results in a reduction of 8:1 in the y-direction, i.e., in the scanning direction. Other image scales are also possible. Image scales with the same sign and absolutely identical in the x- and y-directions, for example, with absolute values ​​of 0.125 or 0.25, are also possible. The number of intermediate image planes in the x- and y-directions in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, can be different. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 A1. Each of the pupil facets 23 is assigned to exactly one of the field facets 21 to form a respective illumination channel for illuminating the object field 5.This can, in particular, result in illumination according to the Köhler principle. The far field is broken down into a plurality of object fields 5 using the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 assigned to them. The field facets 21 are each imaged onto the reticle 7 by an assigned pupil facet 23, superimposed on one another, to illuminate the object field 5. The illumination of the object field 5 is, in particular, as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels. The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by an arrangement of the pupil facets.By selecting the illumination channels, in particular the subset of pupil facets that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting. Likewise, preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels. Further aspects and details of the illumination of the object field 5 and, in particular, of the entrance pupil of the projection optics 10 are described below. The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible. The entrance pupil of the projection optics 10 cannot usually be precisely illuminated using the pupil facet mirror 22.When imaging the projection optics 10, which telecentrically images the center of the pupil facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found in which the pairwise determined distance of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugated to it in spatial space. In particular, this surface exhibits a finite curvature. The projection optics 10 may have different positions of the entrance pupil for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.In the arrangement of the components of the illumination optics 4 shown in Figure 1, the pupil facet mirror 22 is arranged in a surface conjugated to the entrance pupil of the projection optics 10. The field facet mirror 20 is arranged tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the second facet mirror 22. Figure 2 shows a schematic meridional section of another projection exposure system 101 for DUV projection lithography, in which the invention can also be used. The structure of the projection exposure system 101 and the principle of imaging are comparable to the structure and procedure described in Figure 1.Identical components are designated by a reference numeral increased by 100 compared to Figure 1, the reference numerals in Figure 2 therefore begin with 101. In contrast to an EUV projection exposure system 1 as described in Figure 1, due to the longer wavelength of the DUV radiation 116 used as useful light in the range from 100 nm to 300 nm, in particular from 193 nm, in the DUV projection exposure system 101 refractive, diffractive and / or reflective optical elements 117, such as lenses, mirrors, prisms, cover plates and the like, can be used for imaging or illumination.The projection exposure system 101 essentially comprises an illumination system 102, a reticle holder 108 for receiving and precisely positioning a reticle 107 provided with a structure, by means of which the subsequent structures on a wafer 113 are determined, a wafer holder 114 for holding, moving, and precisely positioning this wafer 113, and a projection lens 110 with a plurality of optical elements 117, which are held via mounts 118 in a lens housing 119 of the projection lens 110. The illumination system 102 provides DUV radiation 116 required for imaging the reticle 107 on the wafer 113. A laser, a plasma source, or the like can be used as the source for this radiation 116.The radiation 116 is shaped in the illumination system 102 via optical elements such that the DUV radiation 116, upon impinging on the reticle 107, has the desired properties with regard to diameter, polarization, wavefront shape, and the like. The structure of the downstream projection optics 101 with the lens housing 119 does not differ fundamentally from the structure described in Figure 1, except for the additional use of refractive optical elements 117 such as lenses, prisms, and cover plates, and will therefore not be described further. Figure 3 shows an inventive connecting element 30, which can be used, for example, as part of a temperature control system in a projection exposure system 1 explained in Figure 1 between a water cabinet (not shown) for providing and preparing temperature control fluid and the mirror M3 (Figure 1). The connecting element 30 comprises a bellows 32.1, 32 at each end.2, each of which is connected to a connection 31.1, 31.2 of a structure of the projection exposure system 1. Furthermore, the connecting element 30 comprises a resonator 40, which has two elastic volume elements designed as bellows 42.1, 42.2 and a coupling element designed as a bend 41. The resonator 40 is connected to the bellows 32.1, 32.2 via two pipe sections 33.1, 33.2. The bend 41 couples the acoustic vibrations transported in the form of longitudinal waves in the fluid 34, which is shown as an arrow in Figure 3, to the resonator 40.The pressure of the fluid 34 acting on the inner surface of the connecting element 30 due to the pressure difference between the pressure in the connecting element 40 and the pressure in the vicinity of the connecting element 40 causes a force FA in the area of ​​the bend 41 due to the smaller area at the inner radius compared to the outer radius, which acts on the bend 41 and thus on the resonator 40 and the connecting element 30. The acoustic vibrations are thus transmitted to the structural mechanics and converted into mechanical vibrations. In the example shown in Figure 3, the force FA causes a deflection Δx (= xA - x0) of the bellows 42.1, 42.2 and thus an increase in volume ΔV (=VA - V0). The bellows 32.1, 32.2 at the connections 31.1, 31.2 serve, in a first approximation, to allow the resonator 40 to vibrate freely and therefore exhibit no or negligible volume increase. This depends on the selected stiffness of the bellows 32.1, 32.2 and the expected acoustic vibrations, the bellows 32.1, 32.2 can also contribute to the volume change. The resonator 40 causes a frequency-dependent reduction or amplification of the fluid pressure p1 at the inlet 35 of the connecting element 30 to the fluid pressure p2 at the outlet 36 of the connecting element 30. The force FA acting on the connecting element 30 causes corresponding lateral, axial, and rotational bearing forces FLKl, FLKa, FLKr at the connections 31.1, 31.2, which are expediently absorbed there in a suitable manner and, if necessary, damped. The operation of the resonator is explained in detail in Figure 4. Figure 4 shows, purely qualitatively, a determined transfer function 37 of the pressure p1, p2 in the fluid 34 from the inlet 35 to the outlet 36, wherein a transfer factor is represented as the ratio of the outlet pressure p2 to the inlet pressure p1.In the lower frequency range, the transmission factor is equal to or close to 1, so the output pressure p2 corresponds to the input pressure p1 in a first approximation. In the example shown in Figure 4, the transfer function 37 exhibits an antiresonance 38 in a specific range in which the transmission factor is lower than 1 by a factor close to 1000. This means that the amplitude of a pressure fluctuation at the input 35 is damped by the resonator by a factor of 0.001, and is therefore significantly reduced or even close to zero at the output 36. Around the antiresonance 38 lies a range 39 in which the transmission factor p2 / p1 is less than 1, meaning that pressure amplitudes in this frequency range from the input 35 to the output 36 of the connecting element 30 are reduced or dampened. In contrast, in the frequency ranges before and after the range 39, the amplitudes are increased.Depending on the sensitivity of the downstream component connected to the connecting element, such as a mirror module, excitations in a frequency range with negative effects can be reduced by the design of the resonator 40. Care must be taken to ensure that excessive frequencies occur in a range that has no or negligible effects on the downstream mirror module. Alternatively, measures to reduce the effects on the downstream component, such as damping, can also be taken, particularly in the case of so-called passive mirror modules, i.e., those with a non-controllable mirror. In the case of a mirror module designed with a controllable mirror, the resonator 40 would ideally be designed such that the excessive amplitudes in the lower frequency range upstream of the reducing region 39 have no negative effects on the mirror.For example, excitations in this frequency range can be adequately controlled by position control of the mirror. The excessive amplitudes in the frequency range after the reducing region 39 are advantageously already in a range that no longer affects the imaging quality of the projection exposure system 1 (Figure 1). Alternatively, the resonator 40 can also be designed such that the largest amplitude of the mechanical oscillations is reduced to a maximum. The connecting element 30 or at least the resonator 40 is designed as an oscillatory system (mass, spring) that can be excited by the mechanical oscillations transmitted via the coupling element. The force FA excites the system, and the resulting deflection, as explained above, leads to a volume change within the resonator 40 (Figure 3).The volume change influences the acoustic impedance, i.e., the relationship between pressure and flow of the fluid 34, and thus a phase shift of the pressure and flow of the fluid. In the case of ideal resonance, the resonator 40 oscillates out of phase with the longitudinal wave (excitation) in the fluid 34, such that the oscillations cancel each other out, or at least almost cancel each other out. Acoustic oscillations of this frequency are thus not transmitted through the connecting element 40, or are transmitted only with significant damping, so that pressure fluctuations of this frequency are no longer present or are minimally present further along the temperature control system. The transmission of the acoustic oscillations via the fluid can thus advantageously be reduced. The bearing forces F. LKl , F LKa , F LKrmust be absorbed by the structure and dampened in a suitable manner so that the energy is removed from the system. Alternatively or additionally, the bearings can also be mounted at insensitive points in the system, or the bearing forces FLKl, FLKa, FLKr can be absorbed at insensitive points in the system. Figures 5a and 5b show two embodiments of a coupling element 41, 43. Figure 5a shows a detail of the connecting element 30, already explained in Figure 3, with the resonator 40, which has a coupling element designed as a bend 41. The bend 41 causes a force FA on the bend 41 due to the fluid pressure p acting on different sized areas on the inner radius and the outer radius. It is clear to a person skilled in the art that a force FA only occurs when the pressure p acts as an overpressure compared to the volume surrounding the bend 41 or the connecting element.The structural rigidity of the manifold 41 is at least a factor of 10 greater than that of the bellows 42.1, 42.2. Ideally, both bellows 42.1, 42.2 are identically constructed and, in particular, have the same rigidity and geometry, particularly diameter. Furthermore, additional masses 47.1, 47.2 can be deliberately attached to interfaces 46.1, 46.2 on the manifold 41 or at other locations on the resonator 40 to influence the resonant frequency of the resonator 40. The greater the oscillating mass and the lower the rigidity of the resonator 40, the greater the volume change and the resulting reduction in the mechanical vibrations transmitted via the fluid 34 in the range of the resonant frequency of the resonator 40. Likewise, the higher the rigidity and the lower the oscillating mass of the resonator 40, the higher the resonant frequency and the smaller the volume change.When designing the resonator 40, it is important to achieve a balance between volume change and frequency, depending on the application and the desired effect. Figure 5b shows a detail of a connecting element 30.1 with another embodiment of a resonator 40.1. This has a coupling element designed as a cone 43, which is connected to two bellows 44.1, 44.2, so that the bellows 44.1, 44.2 and the cone 43 lie on the same central axis 45. Similar to the elbow 41, the cone 43 causes a force FA due to the reduction of the cross-section during pressure fluctuations. This force leads to an elongation Δx1 of the bellows 44.1 and a compression Δx2 of the bellows 44.2. The structural rigidity of the cone 43 is at least a factor of 10 greater than that of the bellows 44.1, 44.2. The bellows 44.1, 44.2 must have different rigidities and / or geometries to generate a volume change in the resonator 40.1.As a result, the difference between the volume changes ΔV1, ΔV2 in the bellows 44.1, 44.2 caused by the elongation Δx1 and compression Δx2 results in a total volume change of ΔVtotal. With the same geometry and stiffness, the volume changes ΔV1, ΔV2 in the bellows 44.1, 44.2 would balance each other out, meaning that resonance cannot develop due to the lack of a phase shift between pressure and flow of the fluid, as explained above. The difference in the respective volume change in the bellows 44.1, 44.2 should be at least 10%. The pipe section can also be designed with a constant diameter, in which case the bellows 44.2 must have a smaller diameter than the pipe section in the flow direction behind the pipe section so that the vibration-induced fluctuation of the fluid pressure p is coupled to the resonator 40.1, thus causing a force FA on the resonator 40.1.As an alternative to cone 43, the pipe section can also have one or more diameter steps down to a smaller diameter. In principle, the resonator 40, 40.1 must have a coupling element that couples the longitudinal waves propagating in the fluid to the resonator, i.e., a force F caused by the longitudinal waves. Aat the coupling element 41, 43. Figures 6a and 6b show different arrangements of resonators 60, 80, 90 in connecting elements 50, 70. Figure 6a shows a connecting element 50 with a resonator 60, wherein the resonator 60 corresponds to the connecting element 50 except for the connections 51.1, 51.2. The resonator 60 has three bellows 62.1, 62.2, 62.3, wherein a first bellows 62.1 and a second bellows 62.2 are connected via a pipe section 63 on the same central axis 65, and the second bellows 62.2 is connected to the third bellows 62.3 via a bend 61. The first bellows 62.1 and the third bellows 62.3 are connected to the connections 51.1, 51.2 of the connecting element 50. The resonator 60 is thus constructed asymmetrically compared to the resonator 40 of Figure 3. The structural rigidity of the pipe section 63 and the elbow 61 is at least a factor of 10 greater than that of the bellows 62.1, 62.2, 62.3.The resulting force FA acts on the bend 61 and thus leads to the deflection and elongation of the bellows 62.1, 62.2, 62.3. These, in turn, cause a volume change, which contributes to the frequency-dependent reduction of the amplitudes of the longitudinal waves in the fluid 34 (Figure 3). When designing the resonator 60, it may be advantageous to design all bellows 62.1, 62.2, 62.3 with different stiffnesses and / or geometries, particularly diameters. The same applies to deliberately arranged additional masses (not shown) on the resonator 60. Figure 6b shows a connecting element 70 with two resonators 80, 90, where the resonators 80, 90 correspond to the connecting element 70 except for the connections 71.1, 71.2.In addition to the first resonator 80, which corresponds in structure to the resonator 60 explained in Figure 6a, the connecting element 70 also comprises a second resonator 90, which is directly connected to the resonator 80, i.e., is arranged in series with the first resonator 80. The two resonators 80, 90 share the bellows 82.3, 92.1, so that the two resonators are directly coupled to each other via this bellows 82.3, 92.1. Depending on the design of the bellows 82.1, 82.2, 82.3, 92.1, 92.2, the pipe section 83, the elbow 81 and the cone 93, as well as the optional additional masses (not shown), the resonators 80, 90 can have two different or one common resonant frequency. In principle, the resonators 80, 90 can also be arranged in space, i.e., as a 3D arrangement, and can resonate in more than just two or even three directions. The connections 71.1, 71.2 on the structure must be selected such that the necessary deflection of the bellows 82.1, 82.2, 82.3, 92.1, 92.2 is not blocked. Furthermore, the desired natural frequency (resonance frequency) must not be suppressed by the connections 71.1, 71.2. It is also conceivable for several connecting elements to be arranged in series in a temperature control system. Connections to the structure can be formed between the individual connecting elements, which absorb the resonators of the connecting elements or the bearing forces of the connecting elements and thereby cause a separation or decoupling of different areas of a projection exposure system 1, 101 (Figure 1, Figure 2). Figure 7 shows a damping element 120 for damping mechanical vibrations in the area of ​​the bellows (Figures 3, 5a to 6b), in particular in the area of ​​the connections (Figures 3, 5a to 6b).The damping element 120 comprises a receptacle 122 for connecting the damping element 120 to the connection 121 of the structure and for receiving a flange 130.1 of a bellows 129. Furthermore, the damping element 120 comprises a receptacle 123 for receiving the second flange 130.2 of the bellows 129 for connection to a pipe section 128. The receptacles 122, 123 each have a frame element 125, 126, each having a recess 131.1, 131.2 into which a damper designed as an O-ring 124 is inserted. The receptacle 122 further has an end stop 127. The O-ring 124 is deformed by a change in length and / or tilting of the bellows 129 and dampens the vibrations or movements of the bellows 129 and thus of the connecting element via the material damping (e.g. dissipation) of the material used for the O-ring 124.The damping element 120 can be used, for example, to damp bearing forces FLKl, FLKa, FLKr acting on the connection 121 through the resonator. In such an application, the damping element 120 also influences the position and amplitude of the resonance frequency and the formation of the reducing region 39 (Figure 4). When using a damping element 120, a balance must be struck between reducing the acoustic vibrations in the fluid and damping the parasitic mechanical vibrations in the structural mechanics. Figure 8 describes a possible method for reducing acoustic vibrations in a connecting element 30, 50, 70, wherein the connecting element 30, 50, 70 connects two components of a projection exposure system 1 and the connecting element 30, 50, 70 is filled with a fluid 34. In a first method step 141, the acoustic vibrations expected in the connecting element are determined.In a second method step 142, the connecting element is designed to at least partially reduce the acoustic vibrations expected in the connecting element. In a third method step 143, an acoustic transfer function of the designed connecting element is determined. In a fourth method step 144, the achieved reduction is compared with a predefined specification based on the transfer function. In a fifth method step 145, the design of the connecting element and the following method steps 142, 143, 144, 145 are repeated until the specification is met.

[0002] List of reference symbols1 Projection exposure system2 Illumination system3 Radiation source4 Illumination optics5 Object field6 Object plane 7 Retikel 8 Reticle holder9 Reticle displacement drive10 Projection optics11 Image field12 Image plane 13 Wafer14 Wafer holder 15 Wafer displacement drive 16 EUV radiation 17 Collector 18 Intermediate focal plane 19 Deflection mirror 20 Facet mirror 21 Facets 22 Facet mirror 23 Facets 30, 30.1 Connecting element 31.1, 31.2 Structure connection 32.1, 32.2 Bellows 33.1, 33.2 Tube section 34 Fluid 35 Entrance Ausgang Transfer functionAntiresonanceSuppression range, 40.1 resonator Krümmer .1,42.2 bellows Konus .1,44.2 Bellows center axis.1,46.2 Interface additional mass.1,47.2 Additional mass connecting element.1,51.2 Connection structure Resonator Krümmer .1-62.3 Bellows Rohrstück Central axis connecting element.1,71.2 Connection structure Resonator Krümmer .1.82.2 bellows Rohrstück Resonator .1.92.2 bellows Konus 1 projection exposure system2 lighting system 7 Retikel 108 Reticle holder 110 Projection optics 113 Wafer114 Wafer holder 116 DUV radiation 117 Optical element 118 Mounts 119 Lens housing 120 Damping device 121 Structure connection 122 Mounting connection 123 Mounting tube section 124 Damper, O-ring 125 Frame element connection 126 Frame element tube section 127 End stop 128 Tube section 129 Balg 130.1,130.2 Flange bellows131.1,131.2 Recess141 Process step 1142 Process step 2143 Process step 3144 Process step 4145 Process step 5M1-M6 Mirrorx0(-x) Length bellows Zero position xA(-x) Length bellows Deflection Δxx Length difference V 0(-x) Volume bellows zero position V A(-x) Volume bellows deflected ΔVx Volume difference FLKa Bearing force axial F LKl Lateral bearing force F LKr Bearing force rotational

Claims

Patent claims1. A method for reducing acoustic vibrations in a connecting element (30, 50, 70), wherein the connecting element (30, 50, 70) connects two components of a projection exposure system and the connecting element (30, 50, 70) is filled with a fluid (34), comprising the following method steps: - determining acoustic vibrations expected in the connecting element (30, 50, 70), - designing the connecting element (30, 50, 70) to at least partially reduce the acoustic vibrations expected in the connecting element (30, 50, 70), - determining an acoustic transfer function (37) of the designed connecting element (30, 50, 70), - comparing the achieved reduction with a previously determined specification based on the transfer function (37), - repeating the design of the connecting element (30, 50, 70) and the following method steps until the specification is met is.2.Method according to claim 1, characterized in that the acoustic vibrations are determined with frequency resolution.

3. Method according to one of claims 1 or 2, characterized in that the connecting element (30, 50, 70) is designed such that at least one section (40, 40.1, 60, 80, 90) of the connecting element (30, 50, 70) resonates due to the determined vibrations.

4. Method according to claim 3, characterized in that a vibration of the section (40, 40.1, 60, 80, 90) caused by the resonance brings about a volume change (ΔV) within the connecting element (30, 50, 70).

5. Method according to one of claims 3 or 4, characterized in that. the design of the connecting element (30, 50, 70) comprises an adjustment of the stiffness of an elastic element (42.1, 42.2, 62.1, 62.2, 62.3, 82.1, 82.2, 92.1, 92.2) encompassed by the section (40, 40.1, 60, 80, 90).

6. Method according to one of claims 3 to 5, characterized in that the design of the connecting element (30, 50, 70) comprises an adjustment of the mass of the section (40, 40.1, 60, 80, 90).

7. Method according to claim 6, characterized in that the mass of the section (40) is adjusted by means of additional masses (47.1, 47.2) detachably connected to components (41) of the section (40, 40.1, 60, 80, 90).

8. Method according to one of the preceding claims, characterized in that the design of the connecting element (30, 50, 70) for at least partially reducing the acoustic vibrations expected in the connecting element (30, 50, 70) is based on sensitive frequency ranges of the component.9.Method according to one of the preceding claims, characterized in that the design of the connecting element (30, 50, 70) for at least partially reducing the acoustic vibrations expected in the connecting element (30, 50, 70) is based on the effects on the imaging quality of the projection exposure system. 10.Connecting element (30, 50, 70) for connecting two components of a projection exposure system (1, 101), wherein the connecting element (30, 50, 70) is filled with a fluid (34), characterized in that the connecting element (30, 50, 70) comprises at least one vibration-reducing section (40, 40.1, 60, 80, 90), wherein the section (40, 40.1, 60, 80, 90) has a coupling element (41, 43, 61, 81, 93) designed as a bend (41, 61, 81). 11.Connecting element (30,50,70) according to claim 10, characterized in that the section (40,40.1,60,80,90) of the connecting element (30,50,70) is designed as a system capable of oscillating. 12.Connecting element (30, 50, 70) according to claim 10, characterized in that the coupling element (43, 93) has a cross-sectional change. 13.Connecting element (30, 50, 70) according to one of claims 10 to 12, characterized in that the section (40, 40.1, 60, 80, 90) has an interface (46.1, 46.2) for connecting additional masses (47.1, 47.2). 14.Connecting element (30, 50, 70) according to one of claims 10 to 12, characterized in that the section (40, 40.1, 60, 80, 90) has an element for changing the volume (32.1, 32.2, 42.1, 42.2, 44.1, 44.2, 62.1, 62.2, 62.3, 82.1, 82.2, 92.1, 92.2, 129).15.Connecting element (30, 50, 70) according to one of claims 10 to 14, characterized in that the acoustic vibrations cause resonance of the section (40, 40.1, 60, 80, 90).16.Connecting element (30, 50, 70) according to claim 15, characterized in that the resonance of the section (40, 40.1, 60, 80, 90) causes a reduction in the amplitude of the acoustic vibration at the resonance frequency.17.Connecting element (30, 50, 70) according to one of claims 10 to 16, characterized in that the connecting element (30, 50, 70) is designed to decouple the transmission of mechanical vibrations.18.Connecting element (30, 50, 70) according to one of claims 10 to 17, characterized in that. the connecting element (30, 50, 70) comprises a damping element (120). A projection exposure system (1, 101) with a connecting element (30, 50, 70) according to one of claims 10 to 18.

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