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

Abstract

The invention relates to methods 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: - Determination of acoustic vibrations expected in the connecting element (30,50,70), - design of the connecting element (30, 50, 70) to at least partially reduce the acoustic vibrations expected in the connecting element (30, 50, 70), - Determination of an acoustic transfer function (37) of the designed connecting element (30, 50, 70), - comparison of the achieved reduction with a predefined specification based on the transfer function (37), - Repeat the design of the connecting element (30,50,70) and the following process steps until the specification is met. Furthermore, the invention relates to a 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) and is characterized in that the connecting element (30, 50, 70) comprises at least one vibration-reducing section (40, 40.1, 60, 80, 90). Furthermore, the invention relates to a projection exposure system (1,101) with a connecting element (30,50,70) according to one of the described embodiments.

Description

[0001] 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.

[0002] Projection exposure systems for semiconductor lithography are used to create extremely fine structures, particularly on semiconductor devices 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 coated with photosensitive material. The minimum dimensions of the created structures depend directly on the wavelength of the light used.

[0003] 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, and especially in the range of 13.5 nm, have been increasingly used. This emission wavelength range is also referred to as the EUV range.

[0004] 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, whose so-called optical effective surfaces are exposed to light, the so-called useful light, during the normal operation of the associated system for imaging and exposure.

[0005] These projection exposure systems are equipped with 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, particularly 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.

[0006] Typically, the temperature control lines, referred to as lines below, are attached to the system structures themselves. The lines are typically 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 as well as good controllability of the system, which is ensured in particular by a minimal delay in the temperature control system.

[0007] Due to its high heat capacity and availability, ultrapure water is typically used as the temperature control fluid; however, other commonly used industrial cooling fluids can also be used. The flowing fluid ensures improved heat transfer across the surfaces through which it flows (forced convection).

[0008] 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 an essential role in relation to the performance of the projection exposure system and the imaging quality of the structures on the wafer.

[0009] The associated pressure waves are longitudinal waves and propagate through the fluid at the speed of sound, i.e., in resonant environments such as stainless steel pipes, at approximately 1500 m / s. These vibrations transmitted through 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 oscillations 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.

[0010] Furthermore, acoustic vibrations can be formed as transmitted vibrations, which originate from mechanical vibrations of the structural mechanics, i.e. the pipes, structures, components and all other mechanical components in direct or indirect connection with the fluid, which are transmitted to the fluid.

[0011] Acoustic and mechanical vibrations are connected or coupled to each other via the pipes / lines and can merge into each other in both directions, whereby 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.

[0012] 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, and structures, and thus of virtually the entire projection exposure system. The sensitivities of the optical system's components to acoustic and mechanical vibrations also play a role.

[0013] In general, 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 negatively impact 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 effects described can negatively impact the image quality of the projection exposure system.

[0014] The object of the present invention is to provide a method for 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.

[0015] 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.

[0016] 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: - Determination of acoustic vibrations expected in the connecting element. - Design of the connecting element to at least partially reduce the acoustic vibrations expected in the connecting element. - Determination of an acoustic transfer function of the designed connecting element. - Comparison of the achieved reduction of acoustic vibrations with a predefined specification based on the transfer function. - Repeat the design of the fastener and the following process steps until the specification is met.

[0017] The process enables the connecting element to be adapted to reduce acoustic vibrations, i.e. vibrations transmitted via the fluid.

[0018] In particular, the acoustic vibrations can be determined with frequency resolution. The acoustic vibrations can generally be determined at a specific 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 a section of the connecting element, which is relevant for reducing the acoustic vibrations, and the frequency ranges in which the acoustic vibrations are reduced, i.e., transmitted by the connecting element with a factor less than 1, can be directly read.

[0019] In a first embodiment, the connecting element can be designed such that at least one section of the connecting element is excited to its resonance by the detected vibrations. This 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 damped by the resonator. This can, for example, be a critical frequency for the stability of a position control system for an optical element.

[0020] In particular, a vibration of the resonator caused by the resonator can cause a volume change, particularly of elastic components or components with a higher degree of compliance than the rest of the piping system (e.g., made of steel) within the connecting element. This 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 out of phase with the acoustic vibration propagating in the fluid in the form of a longitudinal wave that the mechanical vibrations of the resonator and the acoustic vibrations in the fluid cancel each other out, or at least almost cancel each other out.

[0021] Acoustic vibrations with a frequency corresponding to the resonant frequency are thus not transmitted through the connecting element, or are transmitted only with significant attenuation. Further along the fluid line system of the projection exposure system, acoustic vibrations of this frequency may have no or only a negligible influence on image quality.

[0022] In a further embodiment, the design of the connecting element can include adjusting the stiffness of an elastic element encompassed by the section. The elastic elements of the resonator, which are predominantly formed as a metallic bellows, can be adjusted by adjusting the material thickness and / or the geometry of the bellows, thereby influencing the oscillatory system of the resonator.

[0023] Furthermore, the design can include adjusting the mass of the section. The mass of the resonator can be adjusted, in particular, using additional masses that are detachably or permanently connected to components of the section. This is particularly useful for adjusting the resonance frequency after the connecting element has been installed, when adjusting the stiffness of the bellows is no longer possible or only possible with increased effort.

[0024] 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 exhibit a natural frequency. This frequency or frequency range does not necessarily have to correspond to or include the maximum of the acoustic vibration itself.

[0025] Furthermore, 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) can be based on the effects on the imaging quality of the projection exposure system. In this case, the mechanical disturbances generated by the acoustic vibrations on a downstream component are multiplied by the optical sensitivities of the optical elements mounted in the component. The optical disturbance caused in this way can, for example, have less effect on the imaging 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. The frequencies of the acoustic vibrations which have the greatest negative effect on the imaging quality are therefore dampened. This frequency orThis frequency range does not necessarily have to correspond to or include the maximum of the acoustic vibration itself.

[0026] 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.

[0027] In a first embodiment, the section of the connecting element can be designed as an oscillating system. With suitable excitation, this system can be excited at its natural frequency and, in combination with a volume change, act as a resonator.

[0028] 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.

[0029] 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 surface sizes at the inner and outer radius of 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, particularly the resonator.

[0030] 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.

[0031] The cross-sectional change in the coupling element can, for example, be conical or step-like and can be realized in a pipe section or at the transition to a bellows.

[0032] 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 be replaced, especially in an already assembled system.

[0033] 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 piece or as a radially at least partially (visco-)elastic coupling element.

[0034] In particular, the resonance of the section corresponding 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 oscillations or acoustic oscillation sources in the fluid, the connecting element can be designed such that at least some of the acoustic oscillations can also be reduced. Acoustic oscillations 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 oscillations and then reduce the oscillations preferably in those frequency ranges, as explained above. This maximum does not necessarily have to be the maximum of the acoustic excitation itself.

[0035] Furthermore, it is also possible to reduce the acoustic vibrations preferably in those frequency ranges which have a negative impact on the image quality of the projection exposure system, as explained above.

[0036] 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, eliminating the need for additional measures to dampen acoustic vibrations. This can advantageously have a positive impact on manufacturing costs and reduce the complexity of the system.

[0037] 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 dampens bearing forces caused by the resonator that occur 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.

[0038] A projection exposure system according to the invention has a connecting element according to one of the preceding embodiments.

[0039] In the following, embodiments and variants of the invention are explained in more detail with reference to the drawings. Fig. 1 schematically shows in meridional section a projection exposure system for EUV projection lithography, Fig. 2 schematically shows in meridional section a projection exposure system for DUV projection lithography, Fig. 3 a first embodiment of a connecting element according to the invention, Fig. 4 a diagram of an acoustic transfer function of a connecting element to explain the mode of operation, Fig. 5a,b a detail of the invention, Fig. 6a,b further embodiments of connecting elements, and Fig. 7 a damping device, and Fig. 8 a flowchart of a possible method for designing a connecting element.

[0040] In the following, with reference to the Fig. 1 describes, by way of example, the essential components of a projection exposure system 1 for microlithography. The description of the basic structure of the projection exposure system 1 and its components is not intended to be limiting.

[0041] One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a radiation source 3, an illumination optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0042] 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.

[0043] In the Fig. 1 shows a Cartesian xyz coordinate system for explanation. The x-direction is perpendicular to the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scanning direction is in the Fig. 1 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0044] The projection exposure system 1 comprises a projection optics 10. The projection optics 10 serves 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.

[0045] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the image plane 12 in the region of the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular along the y-direction, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0046] The radiation source 3 is an EUV radiation source. The radiation source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation has, in particular, a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example, an LPP source (laser produced plasma) or a DPP source (gas discharged produced plasma). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free-electron laser (FEL).

[0047] The illumination radiation 16 emanating from the radiation source 3 is focused by a collector 17. The collector 17 can 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.

[0048] 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.

[0049] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. 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. Of these facets 21, Fig. 1 only some examples are shown.

[0050] 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.

[0051] As is known, for example, from DE 10 2008 009 600 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 10 2008 009 600 A1.

[0052] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction.

[0053] 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 1 614 008 B1, and US Pat. No. 6,573,978.

[0054] 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.

[0055] The second facets 23 can also be macroscopic facets, which can, for example, be round, rectangular, or hexagonal, or alternatively facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0056] The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces.

[0057] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (fly's eye integrator).

[0058] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugated 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 10 2017 220 586 A1.

[0059] 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 before the object field 5.

[0060] 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 into 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, grazing incidence mirrors).

[0061] The illumination optics 4 has in the version shown in the Fig. 1, after the collector 17 there are exactly three mirrors, namely the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

[0062] In a further embodiment of the illumination optics 4, the deflection 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.

[0063] 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 usually only an approximate imaging.

[0064] 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.

[0065] In the Fig. 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 M1 are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 is a doubly obscured optic. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0066] Reflection surfaces of the mirrors Mi can be designed as freeform surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one rotational symmetry axis of the reflection surface shape. The mirrors Mi, 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.

[0067] The projection optics 10 has 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.

[0068] The projection optics 10 can, in particular, be anamorphic. It has, in particular, different magnifications 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 imaging without image inversion. A negative sign for the magnification β means imaging with image inversion.

[0069] The projection optics 10 thus leads to a reduction in the ratio 4:1 in the x-direction, i.e. in the direction perpendicular to the scanning direction.

[0070] The projection optics 10 results in a reduction of 8:1 in the y-direction, i.e. in the scanning direction.

[0071] Other magnifications are also possible. Magnifications 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.

[0072] 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 can vary depending on the design of the projection optics 10. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 A1.

[0073] 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 divided 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.

[0074] The field facets 21 are each imaged onto the reticle 7 by an associated 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.

[0075] By arranging the pupil facets, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. By selecting the illumination channels, in particular the subset of the 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.

[0076] A 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.

[0077] 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.

[0078] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0079] The entrance pupil of the projection optics 10 cannot usually be precisely illuminated with the pupil facet mirror 22. When the projection optics 10 images the center of the pupil facet mirror 22 telecentrically 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 conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

[0080] It is possible that the projection optics 10 have different entrance pupil positions 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.

[0081] In the Fig. 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.

[0082] The first facet mirror 20 is arranged tilted to an arrangement plane which is defined by the second facet mirror 22.

[0083] Fig. 2 shows a schematic meridional section of another projection exposure system 101 for DUV projection lithography, in which the invention can also be used.

[0084] The structure of the projection exposure system 101 and the principle of imaging is comparable to that in Fig. 1 described structure and procedure. Identical components are provided with a 100 Fig. 1 raised reference numerals, the reference numerals in Fig. So 2 start with 101.

[0085] In contrast to a Fig. 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, refractive, diffractive and / or reflective optical elements 117, such as lenses, mirrors, prisms, cover plates and the like, can be used in the DUV projection exposure system 101 for imaging or for 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 later 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.

[0086] 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, exhibits the desired properties with regard to diameter, polarization, wavefront shape, and the like.

[0087] The structure of the subsequent projection optics 101 with the lens housing 119 does not differ in principle from that in Fig. 1 and is therefore not described further.

[0088] Fig. 3 shows an inventive connecting element 30, which can be used, for example, as part of a temperature control system in a Fig. 1 explained projection exposure system 1 between a water cabinet (not shown) for the provision and preparation of tempering fluid and the mirror M3 ( Fig. 1) can be used. The connecting element 30 comprises a bellows 32.1, 32.2 at each end, which is connected to a connection 31.1, 31.2 of a structure of the projection exposure system 1.

[0089] 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.

[0090] The manifold 41 couples the fluid 34, which is in the Fig. 3 is shown as an arrow, in the form of longitudinal waves transported acoustic vibrations with 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 environment of the connecting element 40 causes a force F in the area of ​​the bend 41 due to the smaller area at the inner radius compared to the outer radius. A , which acts on the manifold 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.

[0091] The force F A caused in the Fig. 3 shown example a deflection Δx (= x A - x0) of the bellows 42.1, 42.2 and thus an increase in volume ΔV (=V A-V0). The bellows 32.1, 32.2 at the connections 31.1, 31.2 serve, as a first approximation, to allow the resonator 40 to vibrate freely and therefore exhibit no or negligible volume increase. Depending on the selected stiffnesses 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.

[0092] 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 F acting on the connecting element 30 A causes corresponding lateral, axial and rotational bearing forces F LKI , F LKa , F LKr at the connections 31.1, 31.2, which are appropriately collected there and damped if necessary. The operation of the resonator is described in the Fig. 4 explained in detail.

[0093] Fig. 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 outlet pressure p2 to inlet pressure p1.

[0094] In the lower frequency range, the transmission factor is equal to or close to 1, so the output pressure p2 corresponds in a first approximation to the input pressure p1. Fig. In the example shown in Figure 4, the transfer function 37 shows an antiresonance 38 in a certain range, in which the transfer factor is lower than 1 by a factor of close to 1000, i.e. an amplitude of a pressure fluctuation at the input 35 is damped by the resonator by a factor of 0.001, i.e. is significantly reduced at the output 36 or is even close to zero.

[0095] Around the antiresonance 38 lies a region 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 damped. In contrast, in the frequency ranges before and after region 39, the amplitudes are increased, i.e., amplified.

[0096] 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 be taken, particularly in the case of so-called passive mirror modules, i.e., those with a non-controllable mirror.

[0097] In the case of a mirror module configured 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 do not have any 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 downstream of the reducing region 39 are advantageously already in a range that no longer affects the imaging quality of the projection exposure system 1 ( Fig. 1) affects.

[0098] Alternatively, the resonator 40 can also be designed in such a way that the largest amplitude of the mechanical vibrations is reduced to a maximum.

[0099] The connecting element 30 or at least the resonator 40 is designed as an oscillating system (mass, spring) that can be excited by the mechanical vibrations transmitted via the coupling element. The force F A excites the system, the resulting deflection, as explained above, leading to a volume change within the resonator 40 ( Fig. 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 relative to each other. 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 therefore 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 LKI , F LKa , F LKrmust be absorbed by the structure and damped appropriately 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 F LKI , F LKa , F LKr be intercepted at insensitive points in the system.

[0100] Fig. 5a and Fig. 5b shows two embodiments of a coupling element 41, 43.

[0101] Fig. 5a shows a detail of the Fig. 3 already explained connecting element 30 with the resonator 40, which has a coupling element designed as a bend 41. The bend 41 causes a force F due to the fluid pressure p acting on different areas on the inner and outer radius. A on the manifold 41. The expert knows that a force F Aonly occurs when the pressure p acts as overpressure compared to the volume surrounding the manifold 41 or the connecting element. The structural rigidity of the manifold 41 is at least 10 times greater than that of the bellows 42.1, 42.2. Ideally, both bellows 42.1, 42.2 are identically designed 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 in order to influence the resonant frequency of the resonator 40. The larger 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 stiffness and the lower the oscillating mass of the resonator 40, the higher the resonance 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.

[0102] Fig. Figure 5b shows a detail of a connecting element 30.1 with a further 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.

[0103] The cone 43 causes a force F similar to the manifold 41 due to the reduction of the cross section in the event of pressure fluctuations. A, which 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.

[0104] Bellows 44.1, 44.2 must have different stiffnesses and / or geometries to generate a volume change in resonator 40.1. This results in a total volume change of ΔV from the difference in the volume changes ΔV1, ΔV2 in bellows 44.1, 44.2 caused by the elongation Δx1 and compression Δx2, respectively. ges .

[0105] With the same geometry and stiffness, the volume changes ΔV1, ΔV2 in bellows 44.1, 44.2 would balance each other out, preventing resonance from occurring due to the lack of phase shift between pressure and fluid flow, as explained above. The difference in the respective volume changes in bellows 44.1, 44.2 should be at least 10%.

[0106] 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, i.e. a force F A at resonator 40.1.

[0107] As an alternative to cone 43, the pipe section can also have one or more diameter steps leading 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 A on the coupling element 41, 43.

[0108] Fig. 6a and Fig. 6b shows different arrangements of resonators 60, 80, 90 in connecting elements 50, 70.

[0109] Fig. 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 via a bend 61 to the third bellows 62.3. 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 therefore, in comparison to the resonator 40, the Fig. 3 asymmetrically constructed.

[0110] The structural rigidity of the pipe section 63 and the bend 61 is at least a factor of 10 greater than that of the bellows 62.1, 62.2, 62.3.

[0111] The resulting force F Aacts on the elbow 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 leads to the frequency-dependent reduction of the amplitudes of the longitudinal waves in the fluid 34 ( Fig. 3) contribute.

[0112] When designing the resonator 60, it may be advantageous to design all bellows 62.1, 62.2, and 62.3 with different stiffnesses and / or geometries, especially diameters. The same applies to deliberately arranged additional masses (not shown) on the resonator 60.

[0113] Fig. 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 is similar in structure to the one shown in the Fig. 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.

[0114] In principle, the arrangement of the resonators 80, 90 can also be spatial, i.e., designed as a 3D arrangement, and can generate resonance in more than just two or even three directions. The connections 71.1, 71.2 to 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 that several connecting elements are 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, thereby separating or decoupling different areas of a projection exposure system 1, 101 ( Fig. 1, Fig. 2) cause.

[0115] Fig. 7 shows a damping element 120 for damping mechanical vibrations in the area of ​​the bellows ( Fig. 3, 5a to 6b), especially in the area of ​​connections ( Fig. 3, 5a to 6b).

[0116] 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. Furthermore, the receptacle 122 has an end stop 127.

[0117] 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.

[0118] The damping element 120 can, for example, be used to damp bearing forces F acting on the connection 121 through the resonator. LKI , F LKa , F LKr apply.

[0119] In the case of an application, the damping element 120 also has an influence on the position and amplitude of the resonance frequency and the formation of the reducing region 39 ( Fig. 4). When using a damping element 120, a balance must be struck between reducing acoustic vibrations in the fluid and damping parasitic mechanical vibrations in the structural mechanics.

[0120] Fig.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 apparatus 1 to one another and the connecting element 30, 50, 70 is filled with a fluid 34.

[0121] In a first method step 141, the acoustic vibrations expected in the connecting element are determined.

[0122] In a second method step 142, the connecting element is designed to at least partially reduce the acoustic vibrations expected in the connecting element.

[0123] In a third method step 143, an acoustic transfer function of the designed connecting element is determined.

[0124] In a fourth method step 144, the achieved reduction is compared with a predefined specification based on the transfer function.

[0125] In a fifth process step 145, the design of the connecting element and the following process steps 142, 143, 144, 145 are repeated until the specification is met. List of reference symbols 1 projection exposure system 2 Lighting system 3 Radiation source 4 Lighting optics 5 Object field 6 Object level 7 reticles 8 reticle holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer holders 15 Wafer relocation drive 16 EUV radiation 17 Collector 18 Intermediate focal plane 19 Deflecting mirrors 20 facet mirrors 21 facets 22 facet mirrors 23 facets 30, 30.1 Connecting element 31.1,31.2 Connection structure 32.1,32.2 bellows 33.1,33.2 Pipe section 34 Fluid 35 Entrance 36 Exit 37 Transfer function 38 Antiresonance 39 Suppression area 40, 40.1 Resonator 41 manifold 42.1,42.2 bellows 43 Cone 44.1,44.2 bellows 45 Central axis 46.1,46.2 Interface additional mass 47.1,47.2 Additional mass 50 connecting element 51.1,51.2 Connection structure 60 resonators 61 manifold 62.1-62.3 Bellows 63 Pipe section 65 central axis 70 connecting element 71.1,71.2 Connection structure 80 Resonator 81 manifold 82.1,82.2 bellows 83 Pipe section 90 Resonator 92.1,92.2 bellows 93 Cone 101 Projection exposure system 102 Lighting system 107 reticles 108 reticle holders 110 Projection optics 113 wafers 114 wafer holders 116 DUV radiation 117 optical element 118 versions 119 lens housings 120 Damping device 121 Connection Structure 122 Recording connection 123 Pipe section holder 124 Damper, O-ring 125 Frame element connection 126 Frame element pipe section 127 End stop 128 pipe section 129 bellows 130.1,130.2 flange bellows 131.1,131.2 recess 141 Process step 1 142 Process step 2 143 Process step 3 144 Process step 4 145 Process step 5 M1-M6 mirrors x 0(-x) Length bellows zero position x A(-x) Length bellows deflection Δx xLength difference V 0(-x) Volume bellows zero position V A(-x) Volume bellows deflected ΔV x Volume difference F LKa Bearing force axial F LKl Lateral bearing force Fı kr Bearing force rotational QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 009 600 A1 [0051, 0055] US 2006 / 0132747 A1

[0053] EP 1 614 008 B1

[0053] US 6,573,978

[0053] DE 10 2017 220 586 A1

[0058] US 2018 / 0074303 A1

[0072]

Claims

[1] 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: - Determination of acoustic vibrations expected in the connecting element (30,50,70), - design of the connecting element (30, 50, 70) to at least partially reduce the acoustic vibrations expected in the connecting element (30, 50, 70), - Determination of an acoustic transfer function (37) of the designed connecting element (30, 50, 70), - comparison of the achieved reduction with a previously defined specification based on the transfer function (37), - Repeat the design of the connecting element (30,50,70) and the following process steps until the specification is met. [2] Method according to claim 1, characterized by that the acoustic vibrations are determined with frequency resolution. [3] Method according to one of claims 1 or 2, characterized by 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 by that a vibration of the section (40,40.1,60,80,90) caused by the resonance causes a volume change (ΔV) within the connecting element (30,50,70). [5] Method according to one of claims 3 or 4, characterized by that the design of the connecting element (30,50,70) comprises an adaptation 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 bythat the design of the connecting element (30,50,70) includes an adaptation of the mass of the section (40,40.1,60,80,90). [7] Method according to claim 6, characterized by 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 by 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 by 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 by that the connecting element (30,50,70) comprises at least one vibration-reducing section (40,40.1,60,80,90). [11] Connecting element (30, 50, 70) according to claim 10, characterized by that the section (40,40.1,60,80,90) of the connecting element (30,50,70) is designed as an oscillatable system. [12] Connecting element (30, 50, 70) according to one of claims 10 or 11, characterized by that the section (40,40.1,60,80,90) has a coupling element (41,43,61,81,93). [13] Connecting element (30, 50, 70) according to claim 12, characterized by that the coupling element is designed as a manifold (41,61,81). [14] Connecting element (30, 50, 70) according to claim 12, characterized bythat the coupling element (43,93) has a change in cross-section. [15] Connecting element (30, 50, 70) according to one of claims 10 to 14, characterized by that the section (40,40.1,60,80,90) has an interface (46.1,46.2) for connecting additional masses (47.1,47.2). [16] Connecting element (30, 50, 70) according to one of claims 10 to 14, characterized by that the section (40,40.1,60,80,90) has a volume change element (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). [17] Connecting element (30, 50, 70) according to one of claims 10 to 16, characterized by that the acoustic vibrations cause a resonance of the section (40,40.1,60,80,90). [18] Connecting element (30, 50, 70) according to claim 17, characterized by that the resonance of the section (40,40.1,60,80,90) causes a reduction of the amplitude of the acoustic oscillation in the resonance frequency. [19] Connecting element (30, 50, 70) according to one of claims 10 to 18, characterized by that the connecting element (30,50,70) is designed to decouple the transmission of mechanical vibrations. [20] Connecting element (30, 50, 70) according to one of claims 10 to 19, characterized by that the connecting element (30,50,70) comprises a damping element (120). [21] Projection exposure system (1,101) with a connecting element (30,50,70) according to one of claims 10 to 20.

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