Optical system, lithography apparatus, method for producing an optical system, and method for designing a vibration damper of an optical system

Abstract

The invention relates to an optical system (200), comprising a component (202), a load-bearing structure (204) for carrying the component (202), a vibration decoupling unit (206) for decoupling the component (202) from a vibration of the load-bearing structure (204), wherein the vibration decoupling unit (206) comprises a first spring element (208) connected to the component (202), a second spring ele- ment (210) connected to the load-bearing structure (204) and an intermediate mass (212) connected to the first spring element (208) and the second spring element (210), wherein a vibration damper (214) connected in parallel with the first spring element (208) is connected to the intermediate mass (212) and the compo- nent (202) or wherein a vibration damper (214) connected in parallel with the second spring element (210) is connected to the intermediate mass (212) and the load-bearing structure (204), wherein the vibration damper (214) comprises at least one damping element (216), by means of which a natural vibration of the intermediate mass (212) can be damped, wherein the vibration damper (214) comprises a damper decoupling unit (300), which is connected in series with the at least one damper element (216).

Description

[0001] Carl Zeiss SMT GmbH

[0002] 1 OPTICAL SYSTEM, LITHOGRAPHY APPARATUS, METHOD FOR PRODUCING AN OPTICAL SYSTEM, AND METHOD FOR DESIGNING A VIBRATION DAMPER OF AN OPTICAL SYSTEM

[0003] The present invention relates to an optical system, a lithography apparatus having such an optical system, a method for producing such an optical system and a method for designing a vibration damper of an optical system.

[0004] The content of the priority application DE 10 2024 208 612.6 is incorporated by reference in its entirety.

[0005] Microlithography is used to produce microstructured structural elements, for example integrated circuits. The microlithography process is performed using a lithography apparatus that comprises an illumination system and a projection system. The image of a mask (reticle) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and is arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0006] Driven by the need for ever smaller structures in the production of integrated circuits, EUV lithography apparatuses that use light at a wavelength in the range from 0.1 nm to 30 nm, in particular 13.5 nm, are currently under development. Since most materials absorb light at this wavelength, such EUV lithography apparatuses require the use of reflective optics units, i.e. mirrors, instead of refractive optics units, i.e. lens elements, as used previously.

[0007] The mirrors may for example be fastened to a force frame and be designed to be at least partially manipulable, in order to allow a movement of a respective mirror in up to six degrees of freedom and consequently allow highly accurate positioning of the mirrors in relation to one another, in particular at the pm level. This allows changes in the optical properties that occur for instance during the operation of the lithography apparatus, for example as a result of thermal influences, to be compensated for.

[0008] Effects inside and outside the EUV lithography apparatus may cause unwanted or parasitic vibrations. Such undesirable vibrations can be caused, for example, by external or internal excitations. These may have a negative impact on the microlithography process in various ways: Firstly, the parasitic vibrations may directly influence the position of a corresponding mirror and / or lens element. Then Carl Zeiss SMT GmbH

[0009] 2 again, they may complicate a stable position control of the corresponding lens element and / or mirror or a position control with high control quality.

[0010] Accordingly, the aim is to isolate critical components, such as mirrors, from parasitic vibrations (this is called vibration isolation). In projection optics units (POB) of EUV lithography apparatuses , decoupling stages are used for vibration damping in order to filter out excitations from external disturbances and thus reduce the movements of the load-bearing structures and hence of the critical components. The use of single-stage or two-stage decoupling stages to filter out the external vibrations is known.

[0011] While a single-stage decoupling stage can be approximated as a "simple" spring for the equivalent circuit diagram, an intermediate mass that is mounted between two springs is used in the case of a two-stage decoupling implementation. This arrangement of the intermediate mass leads to an internal resonance on account of inertia effects and must be damped in order to reduce negative effects of the intermediate mass on the performance of the EUV lithography apparatus. In the design of such a two-stage decoupling stage or such a damping system, it is necessary to find a compromise between an achievable damping effect of the damping system and only a limited transfer of external excitations to the intermediate mass (dynamic stiffness), especially at high frequencies.

[0012] In a two-stage decoupling stage, an intermediate mass is connected between two springs or spring elements. One of the spring elements is connected to a vibration-transmitting and / or vibration-excited structure of the EUV lithography apparatus. The other spring element is connected to the structure to be decoupled or damped. In order to dampen the internal resonance of the intermediate mass, especially at high vibration frequencies, it is possible to use what is frequently referred to as a tuned mass damper together with the intermediate mass. In conjunction with the two-stage decoupling stage (the spring-intermediate massspring package), this tuned mass damper is tuned to an internal resonant frequency of the intermediate mass of the damping system in such a way that a predetermined degree of damping is achieved for the entire damping system.

[0013] In an alternative, a position and / or acceleration of the intermediate mass can be detected, and a damping force can be introduced by way of an actuator in order thus to actively counteract an unwanted movement of the intermediate mass. This damping system offers a high degree of design freedom but leads to higher costs and significant qualification outlay. In addition, this embodiment requires fibres and / or power cables, which might influence the dynamic behaviour Carl Zeiss SMT GmbH

[0014] 3

[0015] (dynamic stiffness) of the decoupling unit. In addition, retrofitting existing EUV lithography apparatuses with an active damping system would lead to a major structural intervention.

[0016] Even though multiple damping systems have already been disclosed in the field of EUV lithography apparatuses, there is still a need for further development, in particular in order to progressively improve a compromise that needs to be found between an achievable damping effect of the damping system and only a limited transfer of external excitations to the intermediate mass (dynamic stiffness), especially at high frequencies.

[0017] Against this background, the problem addressed by the present invention is that of providing at least one improved optical system.

[0018] Accordingly, an optical system is proposed, comprising a component, a load-bearing structure for carrying the component, a vibration decoupling unit, in particular a two-stage vibration decoupling unit, for decoupling the component from a vibration of the load-bearing structure, in particular an undesirable or parasitic vibration, wherein the vibration decoupling unit comprises a first spring element connected to the component, a second spring element connected to the load-bearing structure and an intermediate mass connected to the first spring element and the second spring element, wherein a vibration damper connected in parallel with the first spring element is connected to the intermediate mass and the component or wherein a vibration damper connected in parallel with the second spring element is connected to the intermediate mass and the load-bearing structure.

[0019] In the present case, the vibration decoupling unit is formed by the first and the second spring element and the intermediate mass provided between the first and second spring elements. Preferably together with the first and second spring elements, the intermediate mass thus forms the two-stage vibration decoupling unit that is provided between the component and the load-bearing structure in order to decouple a vibration of the load-bearing structure from the component.

[0020] Vibration decoupling with the vibration damper connected in parallel with the second spring element preferably means that the vibration damper is connected in parallel with the first spring element or the second spring element of the vibration decoupling unit in order thus to dampen a vibration behaviour of the intermediate mass, in particular in the event of resonance. By connecting the vibration damper in parallel, the resonant frequency of the entire system, especially of Carl Zeiss SMT GmbH

[0021] 4 the vibration decoupling unit, is lowered, and the vibration transfer to the component is minimized. The resilient connection of the vibration damper to the intermediate mass and the load-bearing structure, in particular on one side (in relation to the intermediate mass), preferably ensures that the dynamic stiffness does not remain constant at high frequencies. In the present case, the vibration damper is secured to the load-bearing structure and to the intermediate mass.

[0022] According to an embodiment, the vibration damper comprises at least one damping element, in particular with a predetermined damping constant, by means of which a natural vibration of the intermediate mass can be damped.

[0023] In the present case, the vibration damper is used to dampen a vibration of the intermediate mass at a resonant frequency or dampen an internal resonance of the intermediate mass, in particular within the scope of vibration decoupling. Vibration dampers may be made from various materials such as rubber, spring steel, foam and / or magnetic materials and should preferably be selected depending on the application and / or vibration frequency.

[0024] The natural vibration of the intermediate mass occurs at a resonant frequency of the intermediate mass in particular, and the latter can be determined, especially analytically, on the basis of a stiffness of the first or the second spring element and a mass of the intermediate mass. In principle, it also appears possible to measure the natural vibration of the intermediate mass, especially at at least one resonant frequency, by means of at least one acceleration sensor or any other motion-related sensor. For example, the measured acceleration can be transformed into the frequency domain in order to determine the natural frequencies of the intermediate mass. The natural frequencies can also be identified by analysis of the transfer function of the entire vibration decoupling unit, for example by identifying the amplitude excesses encompassed by the transfer function of the vibration decoupling unit. In principle, the natural vibration of the intermediate mass may also be determined by way of a finite element method (FEM), in which the vibration behaviour of the vibration decoupling unit is simulated. Using the FEM, it is possible to determine the natural frequencies and / or natural modes of an intermediate mass before it is actually produced. For example, this also allows a geometry of the intermediate mass to be optimized in order to further minimize resonances.

[0025] According to an embodiment, the vibration damper comprises a damper decoupling unit, which is connected in series with the at least one damper element. Carl Zeiss SMT GmbH

[0026] 5

[0027] The damping element, in particular arranged on one side, is preferably connected in series with an additional mass, for example constructionally to a holder. The additional holder has a defined stiffness in order to thus filter the damper force at high frequencies.

[0028] The vibration damper therefore preferably not only comprises a damper element for damping natural vibrations of the intermediate mass but also has a further damper decoupling unit, which is connected in series with the damper element in order to further improve the damping properties of the vibration damper.

[0029] According to an embodiment, the damper decoupling unit comprises a third spring element connected to the damping element, a fourth spring element connected to the load-bearing structure or to the component and a mass connected to the third spring element and the fourth spring element.

[0030] The damper decoupling unit therefore preferably forms a two-stage vibration decoupling means, in which the mass, in a manner similar to the vibration decoupling unit, is placed between the third and the fourth spring element. The mass preferably refers to a mass of a holder and / or of a receptacle and / or of a loadbearing structure of the damping element. Alternatively, the mass may be referred to as decoupling mass or load-bearing mass. The third and fourth spring elements preferably have the same stiffness. The damper decoupling unit together with the damping element preferably forms a modified embodiment of a relative damper, and hence preferably forms a passive damping system that is used to reduce vibrations of the intermediate mass. The modified relative damper comprises the mass, which is arranged between two spring elements and in series with the damper element. The functionality of the masses connected to the relative damper preferably comprises two working states. For frequencies in the range of the resonances of the intermediate mass to be damped, the mass moves with the excitation side (lower base point). The damper therefore works approximately like a conventional relative damper. For higher frequencies (defined by the mass and the connecting springs), the mass is at rest, and so, to an approximation, the damper is unable to transmit any forces due to a base point excitation.

[0031] According to an embodiment, the vibration damper is connected to the intermediate mass and the load-bearing structure, in each case by way of a releasable connection, in particular a holder, and / or by a clamp. The holder preferably comprises a defined mass and / or stiffness in order to be used in this way, in particular for the purpose of low-pass filtering. Carl Zeiss SMT GmbH

[0032] 6

[0033] As a result, in particular depending on the available installation space, an existing optical system comprising a vibration decoupling unit can be retrofitted and / or supplemented to include a vibration damper of the present type, and so, optionally, the damping properties and hence a vibration decoupling behaviour of the optical system can be improved retrospectively. In principle, the connection of the vibration damper to the load-bearing structure and the intermediate mass can be realized by way of any, preferably mechanical connection. With particular preference, the mechanical connections are designed to be as simple as possible in order thus to reduce negative effects, which might be caused by a mechanical connection, on a vibration decoupling of the component and / or a damping of a vibration behaviour of the intermediate mass. In principle, however, other integrally bonded and / or frictional connection types are also conceivable for connecting the vibration damper to the load-bearing structure and the intermediate mass.

[0034] According to an embodiment, the load-bearing structure comprises a support structure and / or a structural component part and / or a housing component and / or a housing profile and / or a support profile of a lithography apparatus.

[0035] Such load-bearing structures of a lithography apparatus preferably serve to hold different component parts of the lithography apparatus and / or to position them relative to each other and / or to mount them in movable fashion. In principle, the load-bearing structure may also be a mount connected to the component and / or an actuator system and / or a sensor system and / or a heat source and / or heat sink and / or a projection lens. Such a load-bearing structure preferably comprises a predetermined stiffness in order to allow, in particular precise, positioning and / or moving and / or mounting and / or holding of an apparatus component part, for example the component in question, in contact with and / or connected to the loadbearing structure. By way of example, the load-bearing structure might be a base plate and / or a scaffold and / or a frame and / or a machine table and / or an arm and / or a component-part carrier and / or a support and / or any other holder, which for example serves to hold and / or position the various apparatus parts of the lithography apparatus, e.g. a vacuum chamber or a gas supply unit. By way of example, the load-bearing structure can be a wafer stage.

[0036] According to an embodiment, the component comprises an optical element, in particular a mirror and / or a lens element and / or a stop, and / or a sensor and / or a sensor frame and / or a partial force frame and / or a force frame for carrying the optical element and / or the sensor. Carl Zeiss SMT GmbH

[0037] 7

[0038] Particularly preferably, the component is a component part of the lithography apparatus, which should be decoupled from external or lithography-apparatus-internal vibrations, for example because a high-precision positioning and / or alignment and / or movement of the component is required to ensure an optimal function of the lithography apparatus that could be disturbed by external or apparatus-internal vibrations. For example, the sensor may comprise a position measuring sensor and / or an acceleration sensor and / or a pressure sensor and / or a force sensor and / or a light sensor and / or any other sensor element. The sensor frame may be provided to hold and / or mount the sensor, preferably in vibration-isolated fashion vis-a-vis surroundings. The partial force frame and / or the force frame is preferably designed to carry a weight and / or absorb external forces that occur during the operation of the lithography apparatus. The partial force frame and / or the force frame preferably mounts and / or holds the respective optical element and / or the respective sensor in a predetermined position, in particular in a fixed position, relative to the partial force frame and / or the force frame. Particularly preferably, a position and / or orientation of the partial force frame and / or the force frame in the lithography apparatus can be modified and / or controlled by at least one actuator.

[0039] The component has in particular six degrees of freedom, preferably three translational degrees of freedom in the x- direction, the y- direction and the z- direction, respectively, and three rotational degrees of freedom about the x-direction, the y- direction and the z-direction, respectively. That is to say, a position and an orientation of the component can be determined or described with the aid of the six degrees of freedom. The "position" of the component should be understood in particular to be its coordinates or the coordinates of a measurement point provided on the component with respect to the x-direction, the ydirection and the z-direction. The "orientation" of the component should be understood to mean in particular its tilt in relation to the three spatial directions. That is to say, the component may be tilted about the x-direction, the ydirection and / or the z-direction. This gives the six degrees of freedom for the position and orientation of the component. A "pose" of the component comprises both its position and its orientation.

[0040] In the present case, a lithography apparatus having at least one optical system according to any one of the embodiments is also proposed.

[0041] The lithography apparatus may comprise multiple optical systems, and so multiple components of the lithography apparatus can be decoupled from external vibrations in the manner described here. The optical system is preferably a Carl Zeiss SMT GmbH

[0042] 8 projection optics unit of the projection exposure apparatus. However, the optical system may also be an illumination system. The projection exposure apparatus may be an EUV lithography apparatus. EUV stands for "extreme ultraviolet" and refers to a wavelength of the operating light of between 0.1 nm and 30 nm. The projection exposure apparatus may also be a DUV lithography apparatus. DUV stands for "deep ultraviolet" and refers to a wavelength of the operating light of between 30 nm and 250 nm.

[0043] A method is moreover proposed for producing such an optical system for a lithography apparatus. The method includes the steps of: a) providing a component, a load-bearing structure for carrying the component and a vibration decoupling unit for decoupling the component from a vibration of the load-bearing structure, wherein the vibration decoupling unit comprises a first spring element, a second spring element and an intermediate mass! b) connecting the first spring element to the component; c) connecting the intermediate mass to the first spring element and the second spring element; d) connecting the second spring element to the load-bearing structure; and e) connecting a vibration damper in parallel with the second spring element to the intermediate mass and the load-bearing structure, in particular in order thus to achieve a low-pass-filtered mode of operation of the vibration damper.

[0044] In principle, any desired connection type can be used to connect or fasten the respective component parts to each other. By preference, the connection type is a releasable connection, for example in order thus to enable a replacement of individual component parts during maintenance and / or repair. In principle, however, the respective component parts may also be connected to each other so as not be disconnectable from each other again.

[0045] A method for designing a vibration damper of an optical system for a lithography apparatus is also proposed. The optical system comprises a component, a loadbearing structure for carrying the component and a vibration decoupling unit for decoupling the component from a vibration of the load-bearing structure, wherein the vibration decoupling unit comprises a first spring element, a second spring element and an intermediate mass, wherein the vibration damper comprises at least one damping element, by means of which a natural vibration of the intermediate mass can be damped, and a damper decoupling unit, which can be connected in parallel with the at least one damper element, wherein the damper decoupling unit comprises a third spring element that is connectable to the damper element, a Carl Zeiss SMT GmbH

[0046] 9 fourth spring element that is connectable to the load-bearing structure and a mass that is connectable to the third spring element and the fourth spring element. The method for designing the at least one vibration damper includes the following steps: a) determining a resonant frequency of the intermediate mass! b) choosing a decoupling frequency, from which a mechanical decoupling of the vibration damper should occur! c) choosing a design parameter, on which a mass of the mass, a resonant frequency of the intermediate mass and a damping constant of the damping element are dependent; and d) determining the mass of the mass and a respective stiffness, in particular a respective dynamic stiffness, of the third and fourth spring elements depending on the chosen decoupling frequency and the chosen design parameter.

[0047] In principle, it is also possible that the step of determining the resonant frequency of the intermediate mass comprises a provision of a pre-determined resonant frequency of the intermediate mass, and so the determination of the resonant frequency need not necessarily be carried out as an active step of the design method. To design the vibration damper, the latter is preferably considered in isolation in order to determine or calculate both the mass and the stiffness, in particular the dynamic stiffness. In this context, it is preferable for a damping constant of the damper element to be known or determined on the basis of the intermediate mass and the stiffness of the first and the second spring element. The damping constant is preferably determined or defined by way of a corresponding selection of the damper element or by way of a corresponding material selection within the scope of selecting the damper element. Particularly preferably, the decoup ling frequency and / or the design parameter can be chosen manually, during the design process of the optical system. In an alternative, the decoupling frequency and / or the design parameter can also be chosen iteratively and / or by simulation, in order thus to find, depending on the vibration decoupling unit, the best possible decoupling frequency and / or design parameter. The mass of the mass and a respective stiffness, in particular a respective dynamic stiffness, of the third and fourth spring elements can preferably be determined analytically, in particular with the aid of a computing device, in particular a computer. In addition to the design parameter, the decoupling frequency, which can be chosen, is also available for designing the optical system, since the required mass is inherently dependent on the chosen decoupling frequency, from which a mechanical decoupling of the vibration damper should occur. This is because, by preference, a higher choice of decoupling frequency allows the chosen mass to be smaller. Optionally, the decoupling frequency may be limited by other boundary conditions Carl Zeiss SMT GmbH

[0048] 10 in the design of the optical system, for example a maximum possible mass of the mass on account of installation space limitations.

[0049] According to an embodiment of the method for designing the vibration damper, the resonant frequency of the intermediate mass is determined by the following equation: where: fmt resonant frequency of the intermediate mass; kint stiffness of the first or the second spring element; and mint mass of the intermediate mass.

[0050] In principle, the stiffness of the respective spring element can also be determined by a static measuring procedure or by a dynamic measuring procedure. In the static measuring procedure, the spring element is preferably positioned under a known load, and the deformation or the spring travel of the spring element is measured. The stiffness can then be determined by calculating the force -to -deformation ratio. This means that the stiffness of the spring element is preferably equal to the applied force divided by the resultant deformation. In the dynamic measuring procedure, the spring element is preferably positioned in a dynamic test setup and subjected to a periodic load, for example by applying a sinusoidal force. The resultant vibration of the spring element is preferably measured. From this, the stiffness can preferably be determined by calculating the resonant frequency and the body force. Particularly preferably, the first spring element comprises the same stiffness as the second spring element.

[0051] According to an embodiment of the method for designing the vibration damper, the mass of the mass (in particular decoupling mass, load-bearing mass, etc.) can be determined by the following equation: where: mdamp mass of the mass; d damping constant of the damper element; a design parameter; fint resonant frequency of the intermediate mass; )0angular frequency, with )0= 2TT0; and Carl Zeiss SMT GmbH

[0052] 11 fo decoupling frequency.

[0053] The mass of the mass preferably determines a volume of the mass, and this might not be allowed to be chosen to be too large, especially in confined spatial conditions.

[0054] According to an embodiment of the method for designing the vibration damper, the stiffness can be determined by the following equation: where: mdamp mass of the mass; k stiffness; )0angular frequency, with )0= 2nf0,' and fo decoupling frequency.

[0055] According to an embodiment of the method for designing the vibration damper, the decoupling frequency is chosen to satisfy f0> 3fint. The decoupling frequency is preferably selected manually or iteratively or by simulation of the optical system, for example by an FEM simulation.

[0056] According to an embodiment of the method for designing the vibration damper, the design parameter should be chosen to satisfy a < 1, particularly preferably satisfy a = 0.5.

[0057] In other words, the design parameter a is preferably chosen such that a < 1, particularly preferably a = 0.5, applies. The design parameter is preferably selected manually or iteratively or by simulation of the optical system, for example by an FEM simulation. In principle, a Bode plot can also be generated for different design parameters and / or different decoupling frequencies, and an optimal and / or desired design parameter and / or an optimal and / or desired decoupling frequency can be selected visually therefrom. In general terms, a Bode plot is a diagram that represents the frequency response of the linear dynamic system. The Bode plot preferably shows the amplitude shift and phase shift of the output variable depending on the frequency of the input variable, in this case the design parameter or the decoupling frequency. The Bode plot is preferably presented with logarithmic scales in order to be able to represent a large frequency range. As a rule, the Bode plot typically has two plots: the amplitude plot and the phase plot. The amplitude plot preferably shows the absolute value or magnitude of the output variable as a function of the input frequency in decibels (dB). The phase plot Carl Zeiss SMT GmbH

[0058] 12 preferably shows the time shift or the phase angle of the output variable as a function of the input frequency in degrees.

[0059] According to an embodiment of the method for designing the vibration damper, the third and fourth spring elements have the same stiffness.

[0060] The aforementioned method steps need not be carried out in the order described but may also be carried out in a different order. Individual component parts of the optical system may also already be prefabricated, for example such that all that is left to carry out is the establishment of the connection of the vibration decoupling unit with the component and the load-bearing structure, in particular including the vibration damper.

[0061] ”A(n); one" in the present case should not necessarily be understood as restrictive to exactly one element. Instead, multiple elements, for example two, three or more, may also be provided. Any other numeral used here should also not be understood as a restriction to exactly the stated number of elements. Rather, numerical deviations upwards and downwards are possible, unless indicated otherwise.

[0062] The embodiments and features described for the optical system apply correspondingly to the proposed methods, and vice versa.

[0063] Further possible implementations of the invention also comprise non -explicitly mentioned combinations of features or embodiments described hereinabove or hereinafter with regard to the exemplary embodiments. A person skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the invention.

[0064] Further advantageous configurations and aspects of the invention are the subject of the dependent claims and of the exemplary embodiments of the invention that are described hereinafter. The invention is elucidated in detail hereinafter by preferred embodiments with reference to the appended figures.

[0065] Fig. 1 shows a schematic meridional section of a projection exposure apparatus for EUV projection lithography!

[0066] Fig. 2 schematically shows an optical system according to a first exemplary embodiment! Carl Zeiss SMT GmbH

[0067] 13

[0068] Fig. 3 schematically shows an optical system according to a second exemplary embodiment;

[0069] Fig. 4 shows a detailed view of a section of the optical system in accordance with Fig. 3;

[0070] Fig. 5 shows a comparison of the dynamic stiffnesses of two known optical systems with the optical system described in Fig. 2 in a Bode plot;

[0071] Fig. 6 shows a flowchart of a method for designing a vibration damper of an optical system for a lithography apparatus in accordance with one exemplary embodiment;

[0072] Fig. 7 shows a dependence of a damping force on a design parameter;

[0073] Fig. 8 shows a comparison of the dynamic stiffnesses of a known optical system with the optical systems described in Fig. 2 and Fig. 3 in a Bode plot;

[0074] Fig. 9 shows a dependence of a dynamic stiffness on a decoupling frequency;

[0075] Fig. 10 shows a flowchart of a method for producing an optical system for a lithography apparatus;

[0076] Fig. 11 shows an optical system from the prior art; and

[0077] Fig. 12 shows a further optical system from the prior art.

[0078] In the figures, identical or functionally identical elements have been provided with the same reference signs, unless indicated otherwise. Furthermore, it should be noted that the illustrations in the figures are not necessarily true to scale.

[0079] Fig. 1 shows one embodiment of a projection exposure apparatus 1 (lithography apparatus), in particular an EUV lithography apparatus. One design of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a light or radiation source 3, an illumination optics unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not comprise the light source 3. Carl Zeiss SMT GmbH

[0080] 14

[0081] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable by way of a reticle displacement drive 9, in particular in a scanning direction.

[0082] Fig. 1 depicts, by way of elucidation, a Cartesian coordinate system with an x-di- rection x, a ydirection y, and a z-direction z. The x-direction x runs perpendicularly into the plane of the drawing. The ydirection y runs horizontally, and the z- direction z runs vertically. The scanning direction runs in the ydirection y in Fig. 1. The z-direction z runs perpendicularly to the object plane 6.

[0083] The projection exposure apparatus 1 comprises a projection optics unit 10. The projection optics unit 10 serves for imaging the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. In an alternative, an angle that differs from 0° is also possible between the object plane 6 and the image plane 12.

[0084] 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 is displaceable by way of a wafer displacement drive 15, in particular in the ydirection y. The displacement, firstly, of the reticle 7 by way of the reticle displacement drive 9 and, secondly, of the wafer 13 by way of the wafer displacement drive 15 can be implemented so as to be synchronized with one another.

[0085] The light source 3 is an EUV radiation source. The light source 3 emits in particular EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. In particular, the used radiation 16 has a wavelength in the range between 5 nm and 30 nm. The light source 3 may be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It may also be a synchrotron-based radiation source. The light source 3 may be a free electron laser (FEL).

[0086] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 may be a collector having one or more ellipsoidal and / or hyperboloidal reflection surfaces. The illumination radiation 16 may be incident on the at least one reflection surface of the collector 17 with grazing incidence (Gl), i.e. at angles of incidence of greater than 45°, or with normal incidence (Nl), i.e. at angles of incidence of less than 45°. The collector 17 may be structured and / or coated on the one hand for optimizing its reflectivity for the used radiation and on the other hand for suppressing extraneous light. Carl Zeiss SMT GmbH

[0087] 15

[0088] Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 may represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics unit 4.

[0089] The illumination optics unit 4 comprises a deflection mirror 19 and, disposed downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 may be a plane deflection mirror or alternatively a mirror with a beam-influencing effect going beyond the pure deflection effect. In an alternative to that or in addition, the deflection mirror 19 may be in the form of a spectral filter that separates a used light wavelength of the illumination radiation 16 from extraneous light of a wavelength deviating therefrom. If the first facet mirror 20 is arranged in a plane of the illumination optics unit 4 which is optically conjugate to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a multiplicity of individual first facets 21, which may also be referred to as field facets. Only some of these first facets 21 are illustrated in Fig. 1 by way of example.

[0090] The first facets 21 may take the form of macroscopic facets, in particular rectangular facets or facets with an arc-shaped or part-circular edge contour. The first facets 21 may take the form of plane facets or, in an alternative to that, convexly or concavely curved facets.

[0091] As is known for example from DE 10 2008 009 600 Al, the first facets 21 themselves can also be composed in each case of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 20 may take the form of a microelectromechanical system (MEMS system) in particular. For details, reference is made to DE 10 2008 009 600 Al.

[0092] The illumination radiation 16 travels horizontally, i.e. in the ydirection y, between the collector 17 and the deflection mirror 19.

[0093] In the beam path of the illumination optics unit 4, a second facet mirror 22 is disposed downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 may also be arranged at a distance from a pupil plane of the illumination optics unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a Carl Zeiss SMT GmbH

[0094] 16 specular reflector. Specular reflectors are known from US 2006 / 0132747 Al, EP 1 614008 Bl and US 6,573,978.

[0095] 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.

[0096] The second facets 23 may likewise be macroscopic facets, which may for example have a round, rectangular or else hexagonal boundary, or can alternatively be facets composed of micromirrors. For details, reference is also made to DE 10 2008 009 600 Al.

[0097] The second facets 23 may have plane or, alternatively, convexly or concavely curved reflection surfaces.

[0098] The illumination optics unit 4 thus forms a doubly faceted system. This fundamental principle is also referred to as a fly's eye integrator.

[0099] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optics unit 10. In particular, the second facet mirror 22 may can be arranged so as to be tilted in relation to a pupil plane of the projection optics unit 10, as described for example in DE 10 2017 220 586 Al.

[0100] The individual first facets 21 are imaged into the object field 5 using the second facet mirror 22. The second facet mirror 22 is the last beam-shaping mirror or else actually the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.

[0101] In a further embodiment (not illustrated) of the illumination optics unit 4, a transfer optics unit contributing in particular to the imaging of the first facets 21 into the object field 5 may be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer optics unit may have exactly one mirror or, alternatively, two or more mirrors, which are arranged in succession in the beam path of the illumination optics unit 4. The transfer optics unit may in particular comprise one or two normal-incidence mirrors (NI mirrors) and / or one or two grazing-incidence mirrors (GI mirrors).

[0102] In the embodiment shown in Fig. 1, the illumination optics unit 4 has exactly three mirrors downstream of the collector 17, specifically the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22. Carl Zeiss SMT GmbH

[0103] 17

[0104] In a further embodiment of the illumination optics unit 4, there is also no need for the deflection mirror 19, and so the illumination optics unit 4 may then have exactly two mirrors downstream of the collector 17, specifically the first facet mirror 20 and the second facet mirror 22.

[0105] The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or using the second facets 23 and a transfer optics unit is, as a rule, only approximate imaging.

[0106] The projection optics unit 10 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

[0107] In the example illustrated in Fig. 1, the projection optics unit 10 comprises six mirrors Ml to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are also possible. The projection optics unit 10 is a doubly obscured optics unit. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics unit 10 has an image-side numerical aperture that is greater than 0.5 and may also be greater than 0.6 and for example may be 0.7 or 0.75.

[0108] Reflection surfaces of the mirrors Mi may take the form of free-form surfaces without an axis of rotational symmetry. In an alternative to that, the reflection surfaces of the mirrors Mi may take the form of aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics unit 4, the mirrors Mi may have highly reflective coatings for the illumination radiation 16. These coatings may be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0109] The projection optics unit 10 has a large object-image shift in the ydirection y between a ycoordinate of a centre of the object field 5 and a ycoordinate of the centre of the image field 11. This object-image shift in the ydirection y may be of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12.

[0110] In particular, the projection optics unit 10 may have an anamorphic design. In particular, it has different imaging scales Bx, By in the x- and y- directions x, y. The two imaging scales Bx, By of the projection optics unit 10 are preferably (Bx, Carl Zeiss SMT GmbH

[0111] 18

[0112] By) = (+ / -0.25, + / -0.125). A positive imaging scale 6 means imaging without image inversion. A negative sign for the imaging scale 6 means imaging with image inversion.

[0113] The projection optics unit 10 consequently leads to a reduction in size with a ratio of 4'1 in the x-direction x, i.e. in a direction perpendicular to the scanning direction.

[0114] The projection optics unit 10 leads to a reduction in size of 8H in the ydirection y, i.e. in the scanning direction.

[0115] Other imaging scales are likewise possible. Imaging scales with the same sign and the same absolute value in the x-direction x and ydirection y are also possible, for example with absolute values of 0.125 or of 0.25.

[0116] The number of intermediate image planes in the x-direction x and in the ydirection y in the beam path between the object field 5 and the image field 11 may be the same or may differ, depending on the embodiment of the projection optics unit 10. Examples of projection optics units with different numbers of such intermediate images in the x-direction x and ydirection y are known from US 2018 / 0074303 Al.

[0117] In each case one of the second facets 23 is assigned to exactly one of the first facets 21 in order to form a respective illumination channel for illuminating the object field 5. This may in particular produce illumination according to the Kohler principle. The far field is decomposed into a multiplicity of object fields 5 with the aid of the first facets 21. The first facets 21 create a plurality of images of the intermediate focus on the second facets 23 respectively assigned thereto.

[0118] By way of an assigned second facet 23, the first facets 21 are each imaged onto the reticle 7 and overlaid on one another for the purpose of illuminating the object field 5. The illumination of the object field 5 is in particular of maximum homogeneity. It preferably has a uniformity error of less than 2%. Field uniformity may be achieved by overlaying different illumination channels.

[0119] An arrangement of the second facets 23 may geometrically define the illumination of the entrance pupil of the projection optics unit 10. The intensity distribution in the entrance pupil of the projection optics unit 10 may be set by selecting the illumination channels, in particular the subset of the second facets 23 that Carl Zeiss SMT GmbH

[0120] 19 guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0121] A likewise preferred pupil uniformity in the region of portions of an illumination pupil of the illumination optics unit 4 that are illuminated in a defined manner can be attained by a redistribution of the illumination channels.

[0122] Further aspects and details of the illumination of the object field 5 and, in particular, of the entrance pupil of the projection optics unit 10 are described below.

[0123] The projection optics unit 10 may have in particular a homocentric entrance pupil. The latter may be accessible. It may also be inaccessible.

[0124] The entrance pupil of the projection optics unit 10 regularly cannot be exactly illuminated with the second facet mirror 22. In the case of imaging by the projection optics unit 10 which telecentrically images the centre of the second facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find an area in which the spacing of the aperture rays that is determined in pairs becomes minimal. This area represents the entrance pupil or an area conjugate thereto in real space. In particular, this area exhibits a finite curvature.

[0125] It may be the case that the projection optics unit 10 has different positions of the entrance pupil for the tangential beam path and for the sagittal beam path. In this case, an imaging element, in particular an optical structural element of the transfer optics unit, should be provided between the second facet mirror 22 and the reticle 7. With the aid of this optical element, the different position of the tangential entrance pupil and of the sagittal entrance pupil may be taken into account.

[0126] In the arrangement of the component parts of the illumination optics unit 4 illustrated in Fig. 1, the second facet mirror 22 is arranged in an area conjugate to the entrance pupil of the projection optics unit 10. The first facet mirror 20 is arranged so as to be tilted with respect to the object plane 6. The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the second facet mirror 22. Carl Zeiss SMT GmbH

[0127] 20

[0128] Fig. 2 shows an optical system 200 in accordance with a first embodiment. The optical system 200 comprises a component 202, a load-bearing structure 204 for carrying the component 202 and a vibration decoupling unit 206.

[0129] By way of example, the component 202 is an optical element, for example one of the mirrors Ml to M6 of the (EUV) lithography apparatus 1 shown in Fig. 1, or a sensor frame.

[0130] For example, the optical system 200 may also be used in a DUV lithography apparatus. The component 202 may also be a lens element and / or a stop and / or a sensor and / or a partial force frame and / or a force frame for carrying the optical element and / or the sensor. The lithography apparatus 1 shown in Fig. 1 by way of example may comprise several such optical systems 200.

[0131] The load-bearing structure 204 may be a support structure and / or a structural component part of the (EUV) lithography apparatus 1, for example a housing part and / or a part of a vacuum chamber or the like, which is excited to vibrate on account of the functionality of the lithography apparatus 1. The vibration decoupling unit 206 is designed to decouple the component 202 from such a vibration or from such vibrations of the load-bearing structure 204 as optimally as possible, for example in order thus to not impair a precision of the lithography apparatus 1 by such vibrations.

[0132] The vibration decoupling unit 206 comprises a first spring element 208 connected to the component 202, a second spring element 210 connected to the load-bearing structure 204 and an intermediate mass 212 connected to the first spring element 208 and the second spring element 210. A vibration damper 214 connected in parallel with the second spring element 210 is connected to the intermediate mass 212 and the load-bearing structure 204.

[0133] The vibration damper 214 comprises at least one damping element 216, by means of which a natural vibration of the intermediate mass 212, for example at a resonant frequency, can be damped. The natural vibration of the intermediate mass 212 for example occurs due to mass inertia effects of the intermediate mass 212. The vibration damper 214 is connected to the intermediate mass 212 and the loadbearing structure 204, in each case by way of a releasable connection 218. In the present case, the releasable connection 218 is designed as a clamp connection by way of example. Carl Zeiss SMT GmbH

[0134] 21

[0135] The embodiment of the vibration damper 214 shown in Fig. 2 is also referred to as variant B2 hereinafter.

[0136] Fig. 3 shows an optical system 200 in accordance with a second embodiment. In this case, the vibration damper 214, which is shown again in Fig. 4 in detailed and isolated form, is supplemented with respect to the embodiment shown in Fig. 2 in such a way that the vibration damper 214 comprises a damper decoupling unit 300 that is connected in series with the at least one damper element 216. The damper decoupling unit 300 preferably takes the form of a two-stage damper decoupling unit. The damper decoupling unit 300 comprises a third spring element 302 connected to the intermediate mass 212, a fourth spring element 304 connected to the load-bearing structure 204 and a mass 306 connected to the third spring element 302 and the fourth spring element 304.

[0137] The embodiment of the vibration damper 214 shown in Figs 3 and 4 is also referred to as variant C hereinafter.

[0138] Since the following figures refer repeatedly to comparisons of the damping properties of different optical systems, two known optical systems 1200, 1300, which are shown as prior art in Figs 11 and 12, are described briefly hereinafter.

[0139] Fig. 11 shows an optical system with what is known as a tuned mass damper (TMD) 1202. The optical system 1200 comprises a component 1204, a load-bearing structure 1206 for carrying the component 1204 and a vibration decoupling unit 1208 for decoupling the component 1204 from a vibration of the load-bearing structure 1206. The component 1204 and load-bearing structure 1206 are only shown schematically. The vibration decoupling unit 1208 comprises a first spring element 1210 connected to the component 1204, a second spring element 1212 connected to the load-bearing structure 1206 and an intermediate mass 1214 connected to the first spring element 1210 and the second spring element 1212. The tuned mass damper TMD 1202 is provided at the intermediate mass 1214 and comprises a third spring element 1216 that is provided between the intermediate mass 1214 and a TMD mass 1218. A damper element 1220 connected in parallel with the third spring element 1216 is provided between the intermediate mass 1214 and the TMD mass 1218.

[0140] The known embodiment of an optical system 1200 described in Fig. 11 is also referred to as comparison variant A hereinafter. Carl Zeiss SMT GmbH

[0141] 22

[0142] Fig. 12 shows a further known optical system 1300. The optical system 1300 comprises a component 1302, a load-bearing structure 1304 for carrying the component 1302 and a vibration decoup ling unit 1306 for decoupling the component 1302 from a vibration of the load-bearing structure 1304. The component 1302 and load-bearing structure 1304 are only shown schematically. The vibration decoupling unit 1306 comprises a first spring element 1308 connected to the component 1302, a second spring element 1310 connected to the load-bearing structure 1304 and an intermediate mass 1312 connected to the first spring element 1308 and the second spring element 1310. A first damper element 1314 is connected in parallel with the third spring element 1308 and connected to the component 1302 and the intermediate mass 1312. A second damper element 1316 is connected in parallel with the second spring element 1310 and connected to the load-bearing structure 1304 and the intermediate mass 1312.

[0143] The known embodiment of an optical system 1300 described in Fig. 12 is also referred to as comparison variant Bl hereinafter.

[0144] A force Ftopis applied to the respective component 202, 1204, 1302 should the respective load-bearing structure 204, 1206, 1304 carry out a movement Xbottom. This relationship can be defined as follows using a Laplace transform:

[0145] Ftop(s) — (s)xbottom(s)

[0146] The force relationship is preferably expressed with the aid of a dynamic stiffness G.

[0147] Fig. 5 shows the above-described force relationship as a function of frequency for comparison variants A and Bl and for variant B2. By way of example, the resonance of the respective intermediate mass 212, 1314, 1312 is at 110 Hz. The damping achieved by the damping element 1220 with the damping constant d is 3% (comparison variant A). The dynamic stiffness of variant A shows a decrease of 40 dB / decade for high frequencies, from approximately 1000 Hz in accordance with Fig. 5. High-frequency excitations are therefore preferably suppressed strongly. Hence, only low forces are transferred to the component 1204. However, a disadvantage of variant A is that the damping element 1220 usually does not achieve significant damping values in all spatial directions x, y, z and / or rotational directions. This leads to excitations in the order of the resonant frequency of the intermediate mass 1208, 110 Hz in the present case, possibly being amplified and having a negative influence on the overall damping performance of the vibration decoupling unit 1208. The low damping of the internal resonant Carl Zeiss SMT GmbH

[0148] 23 frequency of the intermediate mass 1214 should therefore be compensated by improving other component parts of the vibration decoupling unit 1208.

[0149] In order to increase the damping and hence the overall damping performance, a respective relative damping element 1314, 1316 with a damping constant of d / 2 is introduced between the component 1204 and the intermediate mass 1214 and between the intermediate mass 1214 and the load-bearing structure 1206 in comparison variant Bl. This allows a damping of 10% to be achieved. However, in accordance with variant Bl, the damping properties have a negative effect on the dynamic stiffness at high frequencies. This is because, as evident from Fig. 5, the dynamic stiffness exhibits a constant behaviour at high frequencies rather than an increasing suppression. The greater transmitted forces at high frequencies in comparison with variant A also have consequences for the control loops used, as they cause an increase in the respective reaction path. Thus, variant Bl does not represent a functionally useful damping solution.

[0150] In comparison with comparison variants A and Bl, the present variant B2 has numerous advantages and leads to improved damping properties. The one-sided use of the damping element 216 between the intermediate mass 212 and the load-bearing structure 204 preferably causes the dynamic stiffness to also have a drop of 20 dB / decade at high frequencies.

[0151] In the present case, variant B2 can still be optimized further such that a compromise as regards the dynamic stiffness of the vibration decoupling unit 206 can be reached between low and high frequency behaviour. Frequencies below 1000 Hz are referred to as low frequency here. Frequencies greater than or equal to 1000 Hz are referred to as high frequency here. The resilient connection of the damping element 216 resulting from the provision of the additional damper decoup ling unit 300 generates low-pass filtering of the damping force that reduces the dynamic stiffness at high frequencies and hence solves the described reaction path problem, in particular as regards comparison variant Bl, and further optimizes this in comparison with the present variant B2.

[0152] To correctly design the component parts of the vibration damper 214, a method for designing the vibration damper 214 of the optical system 200 is proposed in the present case and described by way of example using the flowchart in Fig. 6. As already described, the optical system 200 according to variant C comprises the component 202, the load-bearing structure 204 for carrying the component 202 and the vibration decoupling unit 206 for decoupling the component 202 from a vibration of the load-bearing structure 204. The vibration decoupling unit 204 comprises Carl Zeiss SMT GmbH

[0153] 24 the first spring element 208, the second spring element 210 and the intermediate mass 212. The vibration damper 214 comprises the at least one damping element 216, by means of which a natural vibration of the intermediate mass 212 can be damped, and the damper decoupling unit 300, which can be connected in series with the at least one damper element 216. The damper decoupling unit 300 comprises the third spring element 302 that is connectable to the damper element 216, the fourth spring element 304 that is connectable to the load-bearing structure 204 and the mass 306 that is connectable to the third spring element 302 and the fourth spring element 304.

[0154] The method for designing the component parts of the vibration damper 214 includes at least the following steps: a) determining S61 a resonant frequency fmt of the intermediate mass 212; b) choosing S62 a decoupling frequency fo, from which a mechanical decoupling of the vibration damper 214 should occur; c) choosing S63 a design parameter a, on which a mass mdamp of the mass 306, the resonant frequency fmt of the intermediate mass 212 and a damping constant d of the damping element 216 are dependent; and d) determining S64 the mass mdamp of the mass 306 and a respective stiffness k of the third and fourth spring elements 302, 304 depending on the chosen decoupling frequency fo and the chosen design parameter a.

[0155] The mass mdamp of the mass 306 can be determined by means of the following equation: where u>0= 2TT0.

[0156] The stiffness can be determined by the following equation:

[0157] The decoupling frequency is preferably chosen such that fQ> 3fint. The inequality can preferably be considered to be a quantitative criterion for recognizing that a vibration decoupling unit 206 meets the present requirements of the design method and / or optical system 200 in accordance with variant C. The decoupling frequency fo is preferably selected manually or iteratively or by simulation of the optical system 200, for example by an FEM simulation. The design parameter a is preferably chosen such that a < 1, particularly preferably such that a = 0.5.

[0158] The inequality can preferably be considered to be a quantitative criterion for Carl Zeiss SMT GmbH

[0159] 25 recognizing that a vibration decoupling unit 206 meets the present requirements of the design method and / or optical system 200 in accordance with variant C.

[0160] Fig. 7 shows the dependence on the design parameter a of the damping force Ftop(s) achievable with the vibration decoupling unit 206 in accordance with variant C. As is customary in a Bode plot, a frequency-force diagram and a phase-frequency diagram are shown here.

[0161] The damping force Ftop(s) can be specified as a function of the damping path s by the following equation:

[0162] It is evident that the damping force Ftop(s) reduces for frequencies above fo, and so mechanical decoupling of the vibration damper 214 is realized. At the point fmt, the damping force Ftop(s) approaches the relative damper element 216 of variant B2 (Fig. 2) for a — > 0. Thus, small values of a produce better damping of the internal resonance fmt of the intermediate mass 212. What emerges is that greater excesses of the damping force Ftop(s) in a region around the decoupling frequency fo can be recorded for a decreasing design parameter a. However, a choice of a smaller design parameter a leads to a greater required mass mdamp of the mass 306. The stiffness k required for the third and fourth spring elements 302, 304 increases with an increased mass mdamp of the mass 306. It was found that a good design compromise can be achieved for a = 0.5.

[0163] Fig. 8 depicts a comparison between the respective dynamic stiffness of comparison variant A and present embodiment variants B2 and C. In variant C, the design parameter a was varied. Here, too, it is clear that choosing the design parameter a to be a = 0.5 allows for a good compromise to be found for the damping of the resonant frequency fmt to be achieved, while at the same time having a low excessive damping force Ftop(s) in the surroundings of the decoupling frequency fo. All designs of variant C have the low-pass filter property of vibration damper 214 in common, and so a drop of 40 dB / decade is also achieved here.

[0164] As mentioned previously, the decoupling frequency is also available as a selectable design variable, in addition to the design parameter a. The dynamic stiffness curves for different settings of the decoupling frequency fo are shown in Fig. 9. The required mass mdamp of the mass 306 in this case depends on the chosen Carl Zeiss SMT GmbH

[0165] 26 decoupling frequency fo. What can be observed here is that the higher the decoupling frequency fo is chosen, the lower the mass mdamp of the mass 306 can be chosen. For the mass mdamp = 0 of the mass 306, the vibration damper 214 of variant C preferably corresponds to a Maxwell element. Overall, it is possible to optimally design the vibration damper 214 with integrated low pass from available installation space, materials and / or technical requirements.

[0166] Fig. 11 shows a flowchart of a method for producing an optical system 200 for a lithography apparatus 1. The method includes the steps of: a) providing Sill a component 202, a load-bearing structure 204 for carrying the component 202 and a vibration decoupling unit 206 for decoupling the component 202 from a vibration of the load-bearing structure 204, wherein the vibration decoupling unit 206 comprises a first spring element 208, a second spring element 210 and an intermediate mass 212; b) connecting Si 12 the first spring element 208 to the component 202; c) connecting Si 13 the intermediate mass 212 to the first spring element 208 and the second spring element 210; d) connecting Si 14 the second spring element 210 to the load-bearing structure 204; and e) connecting Si 15 a vibration damper 214 in parallel with the second spring element 210 to the intermediate mass 212 and the load-bearing structure 204.

[0167] Although the present invention has been described with reference to exemplary embodiments, it is modifiable in a variety of ways.

[0168] Carl Zeiss SMT GmbH

[0169] 27

[0170] LIST OF REFERENCE SYMBOLS

[0171] 1 Projection exposure apparatus

[0172] 2 Illumination system

[0173] 3 Light source

[0174] 4 Illumination optics unit

[0175] 5 Object field

[0176] 6 Object plane

[0177] 7 Reticle

[0178] 8 Reticle holder

[0179] 9 Reticle displacement drive

[0180] 10 Projection optics unit

[0181] 11 Image field

[0182] 12 Image plane

[0183] 13 Wafer

[0184] 14 Wafer holder

[0185] 15 Wafer displacement drive

[0186] 16 Illumination radiation

[0187] 17 Collector

[0188] 18 Intermediate focal plane

[0189] 19 Deflection mirror

[0190] 20 First facet mirror

[0191] 21 First facet

[0192] 22 Second facet mirror

[0193] 23 Second facet

[0194] 200 Optical system

[0195] 202 Component

[0196] 204 Load-bearing structure

[0197] 206 Vibration decoupling unit

[0198] 208 First spring element

[0199] 210 Second spring element

[0200] 212 Intermediate mass

[0201] 214 Vibration damper

[0202] 216 Damping element

[0203] 218 Releasable connection

[0204] 300 Damper decoupling unit

[0205] 302 Third spring element

[0206] 304 Fourth spring element

[0207] 306 Mass

[0208] 1200 Optical system (prior art) Carl Zeiss SMT GmbH 28 1202 Tuned mass damper

[0209] 1204 Component

[0210] 1206 Load-bearing structure

[0211] 1208 Vibration decoupling unit

[0212] 1210 First spring element

[0213] 1212 Second spring element

[0214] 1214 Intermediate mass

[0215] 1216 Third spring element

[0216] 1218 TMD mass

[0217] 1220 Damper element

[0218] 1300 Optical system (prior art)

[0219] 1302 Component

[0220] 1304 Load-bearing structure

[0221] 1306 Vibration decoupling unit

[0222] 1308 First spring element

[0223] 1310 Second spring element

[0224] 1312 Intermediate mass

[0225] 1314 First damper element

[0226] 1316 Second damper element a Design parameter d Damping constant of the damper element fint Resonant frequency of the intermediate mass fo Decoupling frequency kint Stiffness k Stiffness mdamp Mass of the mass m^t Mass of the intermediate mass c o Angular frequency

[0227] Ml Mirror

[0228] M2 Mirror

[0229] M3 Mirror

[0230] M4 Mirror

[0231] M5 Mirror

[0232] M6 Mirror

Claims

Carl Zeiss SMT GmbH29 CLAIMS1. Optical system (200), comprising: a component (202), a load-bearing structure (204) for carrying the component (202), a vibration decoupling unit (206) for decoupling the component (202) from a vibration of the load-bearing structure (204), wherein the vibration decoupling unit (206) comprises a first spring element (208) connected to the component (202), a second spring element (210) connected to the load-bearing structure (204) and an intermediate mass (212) connected to the first spring element (208) and the second spring element (210), wherein a vibration damper (214) connected in parallel with the first spring element (208) is connected to the intermediate mass (212) and the component (202) or wherein a vibration damper (214) connected in parallel with the second spring element (210) is connected to the intermediate mass (212) and the loadbearing structure (204), wherein the vibration damper (214) comprises at least one damping element (216), by means of which a natural vibration of the intermediate mass (212) can be damped, wherein the vibration damper (214) comprises a damper decoupling unit (300), which is connected in series with the at least one damper element (216).

2. Optical system according to Claim 1, wherein the damper decoupling unit (300) comprises a third spring element (302) connected to the damper element (216), a fourth spring element (304) connected to the load-bearing structure (204) or to the component (202) and a mass (306) connected to the third spring element (302) and the fourth spring element (304).

3. Optical system according to Claim 1 or 2, wherein the vibration damper (214) is connected to the intermediate mass (212) and the load-bearing structure (204), in each case by way of a releasable connection (218), in particular a holder, and / or by a clamp.

4. Optical system according to any of Claims 1-3, wherein the load-bearing structure (204) comprises a support structure and / or a structural component part.

5. Optical system according to any of Claims 1'4, wherein the component (202) comprises an optical element, in particular a mirror (M1-M6) and / or a lens element and / or a stop, and / or a sensor and / or a sensor frame and / or a partial force frame and / or a force frame for carrying the optical element and / or the sensor.Carl Zeiss SMT GmbH306. Lithography apparatus (1) having an optical system (200) according to any of Claims 1 to 5.

7. Method for producing an optical system (200) for a lithography apparatus (1), including the following steps: a) providing a component (202), a load-bearing structure (204) for carrying the component (202) and a vibration decoupling unit (206) for decoupling the component (202) from a vibration of the load-bearing structure (204), wherein the vibration decoupling unit (206) comprises a first spring element (208), a second spring element (210) and an intermediate mass (212); b) connecting the first spring element (208) to the component (202); c) connecting the intermediate mass (212) to the first spring element (208) and the second spring element (210); d) connecting the second spring element (210) to the load-bearing structure (204); and e) connecting a vibration damper (214) in parallel with the second spring element (210) to the intermediate mass (212) and the load-bearing structure (204), wherein the vibration damper (214) comprises at least one damping element (216), by means of which a natural vibration of the intermediate mass (212) can be damped, wherein the vibration damper (214) comprises a damper decoupling unit (300), wherein the method comprises the step: f) connecting the damper decoupling unit (300) in series with the at least one damper element (216).

8. Method for designing a vibration damper (214) of an optical system (200) for a lithography apparatus (1), comprising a component (202), a load-bearing structure (204) for carrying the component (202) and a vibration decoupling unit (206) for decoupling the component (202) from a vibration of the load-bearing structure (204), wherein the vibration decoupling unit (204) comprises a first spring element (208), a second spring element (210) and an intermediate mass (212); wherein the vibration damper (214) comprises at least one damping element (216), by means of which a natural vibration of the intermediate mass (212) can be damped, and a damper decoupling unit (300), which can be connected in series with the at least one damper element (216); wherein the damper decoupling unit (300) comprises a third spring element (302) that is connectable to the damper element (216), a fourth spring element (304) that is connectable to the load-bearing structure (204) and a mass (306)Carl Zeiss SMT GmbH31 that is connectable to the third spring element (302) and the fourth spring element (304); the method including the steps of: a) determining (S61) a resonant frequency (fmt) of the intermediate mass (212); b) choosing (S62) a decoupling frequency (fo), from which a mechanical decoupling of the vibration damper (214) should occur; c) choosing (S63) a design parameter (a), on which a mass (mdamp) of the mass (306), the resonant frequency (fmt) of the intermediate mass (212) and a damping constant (d) of the damping element (216) are dependent; and d) determining (S64) the mass (mdamp) of the mass (306) and a respective stiffness (k) of the third and fourth spring elements (302, 304) depending on the chosen decoup ling frequency (fo) and the chosen design parameter (a).

9. Method according to Claim 8, wherein the mass (mdamp) of the mass (306) can be determined by the following equation:where u>0= 2TT0.

10. Method according to Claim 8 or 9, wherein the stiffness (k) can be determined by the following equation:

11. Method according to any of Claims 8'10, wherein the decoupling frequency (fo) should be chosen to satisfy f0> 3fint.

12. Method according to any of Claims 8-11, wherein the design parameter (a) should be chosen to satisfy a < 1, particularly preferably satisfy a = 0.5.

13. Method according to any of Claims 8'12, wherein the third and fourth spring elements (302, 304) have the same stiffness (k).

Images