DE102022211799A1 - MANIPULATOR, OPTICAL SYSTEM, PROJECTION EXPOSURE EQUIPMENT AND PROCESS - Google Patents

Abstract

A manipulator (134, 136) for adjusting an optical element (102, 102'), having a magnet assembly (142, 168) which can be coupled to the optical element (102, 102'), and a coil assembly (152, 178) which can be displaced linearly with the aid of the magnet assembly (142, 168) in order to adjust the optical element (102, 102'), the coil assembly (152, 178) having an exchangeable mass element (206 , 214).

Description

The present invention relates to a manipulator for adjusting an optical element, an optical system with such a manipulator, a projection exposure system with such a manipulator and/or such an optical system and a method for adjusting the natural frequency of such a manipulator.

Microlithography is used to produce microstructured components such as integrated circuits. The microlithography process is carried out using a lithography system which has an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example a silicon wafer, in order to place the mask structure on the light-sensitive coating of the substrate transferred to.

Driven by the striving for ever smaller structures in the manufacture of integrated circuits, EUV lithography systems are currently being developed which use light with a wavelength in the range from 0.1 nm to 30 nm, in particular 13.5 nm. In such EUV lithography systems, because of the high absorption of light of this wavelength by most materials, reflective optics, ie mirrors, must be used instead of—as hitherto—refractive optics, ie lenses.

In exposure mode it is necessary to adjust the mirrors of the projection system. Manipulators, in particular so-called voice coil manipulators (VCM), can be used for this purpose. Such a manipulator forms a spring-mass-damper system, which decouples the mirror from a fixed world, in particular from a support frame (Engl .: Force Frame). This is to prevent the transmission of high-frequency vibrations. The natural frequency of the manipulator should be within a given specification. However, due to complex process fluctuations and/or production fluctuations, the required natural frequency cannot always be kept within the specification. This can lead to a costly and time-consuming reworking process on the manipulator. This needs to be improved.

Against this background, an object of the present invention is to provide an improved manipulator for adjusting an optical element.

Accordingly, a manipulator for adjusting an optical element is proposed. The manipulator includes a magnet assembly that can be coupled to the optical element, and a coil assembly that can be linearly displaced with the help of the magnet assembly in order to adjust the optical element, the coil assembly having an exchangeable mass element for adjusting the natural frequency of the manipulator.

Because the exchangeable mass element is provided, it is possible to influence the natural frequency of the manipulator by exchanging or changing the mass element in such a way that the natural frequency lies within a predetermined specification. Complex post-processing of the manipulator before it is integrated into an optical system can be omitted.

The main influencing factor for the natural frequency is the rigidity and the mass of an entire spring-mass-damper system of the manipulator. In the present context, “rigidity” means the resistance of a body to elastic deformation caused by an external load. The rigidity is determined by the material used for the body and its geometry. Since the adjustment of the rigidity is not or only very difficult to implement for process reasons, such as installation space, cleaning, cleanliness or the like, in terms of costs and/or benefits, the natural frequency is preferably adjusted here by varying the mass of the mass element.

The manipulator can also be referred to as an actuator, actuator, setting element or setting device. Preferably, two manipulators each form a manipulator arrangement. The optical element can be a mirror, in particular an EUV mirror. However, the optical element can also be a lens. However, the optical element is preferably a mirror and comprises a mirror substrate and an optically effective surface attached to the mirror substrate. The optically effective surface is set up to reflect illumination radiation, in particular EUV radiation. The optically effective surface can be a mirror surface.

A coordinate system with a first spatial direction or x-direction, a second spatial direction or y-direction and a third spatial direction or z-direction is assigned to the manipulator. The spatial directions are oriented perpendicular to one another. The optical element or the optically effective surface has six degrees of freedom, namely three translational degrees of freedom in each case along the x-direction, the y-direction and the z-direction, and three rotational degrees of freedom respectively about the x-direction, the y-direction and the z-direction. This means that a position and an orientation of the optical element or the optically effective surface can be determined or described using the six degrees of freedom.

The “position” of the optical element or the optically effective surface is to be understood in particular as its coordinates or the coordinates of a measuring point provided on the optical element with respect to the x direction, the y direction and the z direction. The “orientation” of the optical element or the optically effective surface is to be understood in particular as its or its tilting with respect to the three spatial directions. This means that the optical element or the optically effective surface can be tilted about the x-direction, the y-direction and/or the z-direction.

This results in the six degrees of freedom for the position and/or orientation of the optical element or the optically effective surface. A “layer” of the optical element or of the optically effective surface preferably includes both its position and its orientation. Accordingly, the term "position" can be replaced by the phrase "position and orientation" and vice versa.

In the present case, “adjusting” or “aligning” the optical element or the optically effective surface is to be understood in particular as changing the position of the optical element or the optically effective surface. For example, the optical element can be moved from an actual position to a target position and vice versa with the aid of a number of such manipulators. For this purpose, for example, six manipulators can be provided, which in particular can each be grouped in pairs to form a manipulator arrangement. The adjustment or alignment of the optical element or the optically effective surface can thus take place in all six aforementioned degrees of freedom.

The magnet assembly preferably includes a magnet, in particular a permanent magnet. The magnet assembly further includes a magnet assembly housing to which the magnet is attached. The magnet assembly housing can be tubular, with the magnet being arranged on the outside of the magnet assembly housing. The magnet assembly can preferably be coupled to the optical element with the aid of its magnet assembly housing. To couple the magnet assembly or the magnet assembly housing to the optical element, a manipulator pin can be provided which is coupled both to the optical element and to the magnet assembly housing.

In the present case, the fact that the magnet assembly can be “coupled” to the optical element means in particular that the magnet assembly can be firmly connected to the optical element, for example with the aid of the magnet assembly housing and the manipulator pin. For this purpose, the optical element preferably has a plurality of mirror sockets, which are provided on the rear side of the optical element, facing away from the optically effective surface. For example, three such mirror sockets are provided. Two such manipulators are preferably coupled to each mirror socket, each in the form of a manipulator arrangement as mentioned above.

The coil assembly preferably includes a coil which is set up to interact with the magnet assembly, in particular with the magnet of the magnet assembly. For this purpose, so-called Lorentz forces act between the coil and the magnet. In addition to the coil, the coil assembly includes a reaction mass. The mass element can be attached to the reaction mass. During operation of the manipulator, the coil assembly interacts with the magnet assembly such that the magnet assembly moves linearly or translationally along a direction of movement relative to the coil assembly. This movement is applied to the optical element in order to adjust it. The fact that the coil assembly can be “linearly displaced” with the help of the magnet assembly means in the present case that the coil assembly moves along a straight line relative to the magnet assembly when the manipulator is in operation.

In the present case, the fact that the mass element is “exchangeable” is to be understood in particular as meaning that the mass element can be connected to the coil assembly, in particular to the reaction mass, and can be detached from it again as often as desired. A connecting element, for example in the form of a screw, can be provided for this purpose. Furthermore, the mass element can also be detachably clamped to the coil assembly. Several different mass elements can be provided, which differ from one another in their masses. To set or change the natural frequency, several mass elements with the same mass or mass elements with different masses can be attached to the coil assembly in order to achieve the desired natural frequency.

In the present case, a “natural frequency setting” is to be understood in particular as meaning that the natural frequency of the manipulator can be changed by exchanging the mass element or several mass elements in such a way that it lies within a required specification. Eigenmodes or normal modes are special movements of an oscillating system, in this case the manipulator. Eigenmodes are periodic movements in which all components of the system show the same frequency if the system is left to its own devices after an excitation. Such a frequency is called the natural frequency of the system, and the corresponding natural mode is also known as natural oscillation. In the present case, the fact that the natural frequency is “set” or “changed” means in particular that the natural frequency is increased or reduced as required. In the present case, the term “natural frequency setting” can be replaced by the term “natural frequency adjustment”.

According to one embodiment, the coil assembly has a reaction mass, with the mass element being releasably attached to the reaction mass.

For example, the mass element is screwed to the reaction mass and/or clamped to it. For example, a modular system with mass elements of different masses can be provided, from which a suitable mass element or several suitable mass elements can be removed and attached to the reaction mass to adapt the natural frequency of the manipulator. The reaction mass is preferably tubular or hollow-cylindrical, it being possible for the magnet assembly housing to pass through the reaction mass.

According to a further embodiment, the coil assembly is coupled to a manipulator housing of the manipulator with the aid of a spring element and with the aid of a damper.

The spring element can be a leaf spring or a helical spring, for example. The coil assembly, the spring element and the damper preferably form a spring-mass damper system of the manipulator. The natural frequency of this spring-mass-damper system is adjusted to adjust the natural frequency of the manipulator. Several spring elements can be provided for connecting the coil assembly to the manipulator housing. The manipulator housing is connected to a fixed world, in particular to a support frame as previously mentioned.

According to a further embodiment, the damper has an eddy current brake.

In particular, the damper is formed by an eddy current brake or the damper is an eddy current brake. In this way, contact-free damping of the coil assembly can be achieved.

According to a further embodiment, the magnet assembly is coupled to the manipulator housing with the aid of spring elements.

The spring elements can be leaf springs. This means in particular that the magnet assembly is mechanically decoupled from the manipulator housing with the aid of the spring elements. In the present case, “mechanically decoupled” means in particular that oscillations or vibrations of the manipulator housing are not, or at least to a reduced extent, transmitted to the magnet assembly with the aid of the spring elements.

According to a further embodiment, the magnet assembly is coupled to the coil assembly with the aid of spring elements.

In this case, the magnet assembly is preferably located within the coil assembly. The spring elements can be leaf spring elements.

According to a further embodiment, the manipulator also has a manipulator pin, which is passed through the magnet assembly at least in sections, it being possible for the magnet assembly to be coupled to the optical element with the aid of the manipulator pin.

The manipulator pin is in particular rod-shaped. As previously mentioned, the manipulator pin is preferably connected to one of the mirror sockets of the optical element. The manipulator pin is preferably passed through the magnet assembly housing at least in sections and is firmly connected to it.

According to a further embodiment, the magnet assembly is passed through the coil assembly at least in sections.

For example, the magnet assembly housing can be passed through the coil assembly. This means in particular that the coil assembly encloses the magnet assembly or the magnet assembly housing at least in sections. Alternatively, the magnet assembly can also be arranged entirely within the coil assembly.

Furthermore, an optical system for a projection exposure system is proposed. The optical system includes an optical element and a manipulator as previously discussed, wherein the magnet assembly is coupled to the optical element.

For example, the magnet assembly is firmly connected to the optical element via the manipulator pin. The optical system can have several such optical elements. The optical elements are preferably mirrors. However, the optical elements can also be lenses. The optical system can be a projection optics or part of a projection optics of the projection exposure system. The optical system can therefore also be referred to as projection optics or projection lens. Alternatively, the optical system can also be an illumination optics or part of such an illumination optics. In the present case, however, it is assumed that the optical system is a projection optics as mentioned above or part of such a projection optics. The optical system preferably includes several manipulators.

According to one embodiment, the optical system also has a first manipulator and a second manipulator, the first manipulator and the second manipulator together forming a manipulator arrangement of the optical system.

This means in particular that the first manipulator and the second manipulator are combined to form the manipulator arrangement. The first manipulator and the second manipulator together form a common assembly, namely the manipulator arrangement. The two manipulators of a manipulator arrangement are coupled to a common mirror socket of the optical element.

According to a further embodiment, a first direction of movement of the first manipulator is oriented at an angle to a second direction of movement of the second manipulator.

In particular, the manipulator pin of the first manipulator moves along the first direction of movement. The manipulator pin of the second manipulator moves along the second direction of movement. The first direction of movement and the second direction of movement are preferably oriented at an angle of inclination of 60° to one another. The manipulator pin of the first manipulator and the manipulator pin of the second manipulator are connected to a common mirror socket of the optical element.

According to a further embodiment, the optical system also has a first manipulator arrangement, a second manipulator arrangement and a third manipulator arrangement, the optical element being adjustable in six degrees of freedom in order to move the optical element from an actual position to a desired position and vice versa , and each manipulator arrangement is assigned two of the six degrees of freedom.

In particular, exactly three manipulator arrangements are provided. Each manipulator arrangement is preferably assigned to a mirror socket of the optical element. The optical element can thus be moved from its actual position to its desired position and vice versa with the aid of the manipulator arrangements. In order to move the optical element from the actual position to the target position, the optical system includes an adjustment device. The adjusting device can include the three manipulator arrangements. Furthermore, the adjustment device includes a control and regulation unit which is set up to control the manipulator arrangements, in particular the manipulators of the manipulator arrangements, in order to adjust or align the optical element.

Furthermore, a projection exposure system with a manipulator as explained above and/or an optical system as explained above is proposed.

The optical system is preferably projection optics of the projection exposure system. However, the optical system can be illumination optics. The projection exposure system can be an EUV lithography system. EUV stands for "Extreme Ultraviolet" and designates a working light wavelength between 0.1 nm and 30 nm. The projection exposure system can also be a DUV lithography system. DUV stands for "Deep Ultraviolet" and describes a working light wavelength between 30 nm and 250 nm.

In addition, a method for adjusting the natural frequency of a manipulator for adjusting an optical element is proposed. In this case, the manipulator has a magnet assembly that can be coupled to the optical element, and a coil assembly that can be linearly displaced with the aid of the magnet assembly in order to adjust the optical element. The method has the following steps: a) detecting a natural frequency of the manipulator, b) determining whether the detected natural frequency is within or outside a predetermined specification, c) replacing a mass element of the coil assembly if the detected natural frequency is outside the predetermined specification, and d) repeating steps a) through c) until the detected natural frequency is within the predetermined specification.

For example, a desired natural frequency of 85 Hz is specified. First, before step a), a middle mass element or standard mass element is mounted on the respective reaction mass. An input measurement then takes place in step b). Based on the initial measurement, it can be assessed in step b) whether the natural frequency is within the permissible specification, above the specification, or below the specification. A tolerance zone can be specified for this. If the achieved natural frequency is within the specification, the manipulator can be integrated into the optical system. If the achieved natural frequency is above the specification, a mass element with a higher mass or an additional mass element can be mounted on the respective reaction mass in step c). Step a) is then carried out again. Depending on whether the achieved natural frequency is then within the specification or not, either the manipulator can be integrated into the optical system or step c) can be carried out again. Steps a) to c) are carried out iteratively until the natural frequency is within specification and the manipulator can be integrated into the optical system. If the achieved natural frequency is below the specification, a mass element with a smaller mass can be mounted on the respective reaction mass in step c). Step a) is then carried out again. Depending on whether the achieved natural frequency is then within the specification or not, either the manipulator can be integrated into the optical system or step c) can be carried out again. In this case too, steps a) to c) are carried out iteratively until the natural frequency is within specification and the manipulator can be integrated into the optical system.

According to one embodiment, after step d), the manipulator is integrated into an optical system which has the optical element.

In the present case, “integration” is to be understood in particular as meaning that the manipulator is built into the optical system. The method is carried out separately for each manipulator or for each manipulator arrangement of the optical system

"A" is not necessarily to be understood as being limited to exactly one element. Rather, a plurality of elements, such as two, three or more, can also be provided. Any other count word used here should also not be understood to mean that there is a restriction to precisely the stated number of elements. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

The embodiments and features described for the manipulator apply correspondingly to the proposed optical system, the proposed projection exposure system and the proposed method and vice versa.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with regard to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

• 1 zeigt einen schematischen Meridionalschnitt einer Projektionsbelichtungsanlage für die EUV-Projektionslithographie;
• 2 zeigt eine schematische Ansicht einer Ausführungsform eines optischen Systems für die Projektionsbelichtungsanlage gemäß 1;
• 3 zeigt eine schematische Aufsicht des optischen Systems gemäß 2;
• 4 zeigt eine schematische Schnittansicht einer Ausführungsform eines Manipulators für das optische System gemäß 2;
• 5 zeigt eine schematische Schnittansicht einer weiteren Ausführungsform eines Manipulators für das optische System gemäß 2;
• 6 zeigt ein schematisches Blockdiagramm einer Ausführungsform eines Verfahren zur Eigenfrequenzeinstellung des Manipulators gemäß 4 oder 5.; und
• 7 zeigt ein schematisches Blockdiagramm einer weiteren Ausführungsform eines Verfahren zur Eigenfrequenzeinstellung des Manipulators gemäß 4 oder 5.

Further advantageous refinements and aspects of the invention are the subject matter of the dependent claims and of the exemplary embodiments of the invention described below. The invention is explained in more detail below on the basis of preferred embodiments with reference to the enclosed figures.

• 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography;
• 2 shows a schematic view of an embodiment of an optical system for the projection exposure apparatus according to FIG 1 ;
• 3 shows a schematic top view of the optical system according to FIG 2 ;
• 4 FIG. 12 shows a schematic sectional view of an embodiment of a manipulator for the optical system according to FIG 2 ;
• 5 FIG. 12 shows a schematic sectional view of another embodiment of a manipulator for the optical system according to FIG 2 ;
• 6 shows a schematic block diagram of an embodiment of a method for adjusting the natural frequency of the manipulator according to FIG 4 or 5 .; and
• 7 shows a schematic block diagram of a further embodiment of a method for adjusting the natural frequency of the manipulator according to FIG 4 or 5 .

Elements that are the same or have the same function have been provided with the same reference symbols in the figures, unless otherwise stated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

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

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 can be displaced via a reticle displacement drive 9, in particular in a scanning direction.

In the 1 a Cartesian coordinate system with an x-direction x, a y-direction y and a z-direction z is drawn in for explanation. The x-direction x runs perpendicularly into the plane of the drawing. The y-direction y runs horizontally and the z-direction z runs vertically. The scanning direction is in the 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

The projection exposure system 1 includes projection optics 10. The projection optics 10 are used to image the object field 5 in an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, there is also an angle other than 0° between the object plane 6 and the Image plane 12 possible.

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

The 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 useful radiation, illumination radiation or illumination light. The useful radiation 16 has in particular a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, for example an LPP source (Engl .: Laser Produced Plasma, plasma generated with the help of a laser). or around a DPP (Gas Discharged Produced Plasma) source. It can also be a synchrotron-based radiation source. The light source 3 can be a free-electron laser (FEL).

The illumination radiation 16 emanating from the light source 3 is bundled 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 in grazing incidence (Engl.: Grazing Incidence, GI), i.e. with angles of incidence greater than 45°, or in normal incidence (Engl.: Normal Incidence, NI), i.e. with incidence angles smaller than 45° , are acted upon by the illumination radiation 16 . The collector 17 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation and on the other hand to suppress stray light.

After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focus plane 18. The intermediate focus plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics 4.

The illumination optics 4 comprises a deflection mirror 19 and a first facet mirror 20 downstream of this in the beam path. The deflection mirror 19 can be a plane deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be designed as a spectral filter, which separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 which is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 20 includes a multiplicity of individual first facets 21, which can also be referred to as field facets. Of these first facets 21 are in the 1 only a few shown as examples.

The first facets 21 can be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 21 can be embodied as planar facets or alternatively as convexly or concavely curved facets.

Like for example from the DE 10 2008 009 600 A1 is known, the ers th facets 21 themselves can also be composed of a large number of individual mirrors, in particular a large number of micromirrors. The first facet mirror 20 can be embodied in particular as a microelectromechanical system (MEMS system). For details refer to the DE 10 2008 009 600 A1 referred.

The illumination radiation 16 runs horizontally between the collector 17 and the deflection mirror 19, ie along the y-direction y.

A second facet mirror 22 is arranged downstream of the first facet mirror 20 in the beam path of the illumination optics 4. 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 , the EP 1 614 008 B1 and the U.S. 6,573,978 .

The second facet mirror 22 includes a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

The second facets 23 can also be macroscopic facets, which can have round, rectangular or hexagonal borders, for example, or alternatively facets composed of micromirrors. In this regard, also on the DE 10 2008 009 600 A1 referred.

The second facets 23 can have plane or alternatively convexly or concavely curved reflection surfaces.

The illumination optics 4 thus forms a double-faceted system. This basic principle is also known as a honeycomb condenser (English: Fly's Eye Integrator).

It can be advantageous not to arrange the second facet mirror 22 exactly in a plane which is optically conjugate to a pupil plane of the projection optics 10 . In particular, the second facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as is the case, for example, in FIG DE 10 2017 220 586 A1 is described.

The individual first facets 21 are imaged in the object field 5 with the aid of the second facet mirror 22 . The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5.

In another embodiment of the illumination optics 4 that is not shown, transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5 , which particularly contributes to the imaging of the first facets 21 in the object field 5 . The transmission optics can have exactly one mirror, but alternatively also have 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 mirror, normal incidence mirror) and/or one or two mirrors for grazing incidence (GI mirror, grazing incidence mirror).

The illumination optics 4 has the version in which 1 shown, exactly three mirrors after the collector 17, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

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.

The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and transmission optics in the object plane 6 is generally only an approximate imaging.

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

At the in the 1 example shown, the projection optics 10 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The projection optics 10 are doubly obscured optics. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture which is greater than 0.5 and which can also be greater than 0.6 and which, for example, is 0.7 or 0.75.

Reflection surfaces of the mirrors Mi can be free-form surfaces without an axis of rotational symmetry be executed. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics 4, the mirrors Mi can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 10 has a large object-image offset in the y-direction y 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 y can be about as large as a z-distance between the object plane 6 and the image plane 12.

The projection optics 10 can in particular be anamorphic. In particular, it has different image scales βx, By in the x and y directions x, y. The two image scales βx, By of the projection optics 10 are preferably at (8x, βy)=(+/−0.25, +/-0.125). A positive imaging scale 6 means imaging without image reversal. A negative sign for the imaging scale β means imaging with image inversion.

The projection optics 10 thus leads to a reduction in the ratio 4:1 in the x-direction x, ie in the direction perpendicular to the scanning direction.

The projection optics 10 lead to a reduction of 8:1 in the y-direction y, ie in the scanning direction.

Other imaging scales are also possible. Image scales with the same sign and absolutely the same in the x and y directions x, y, for example with absolute values of 0.125 or 0.25, are also possible.

The number of intermediate image planes in the x and y directions x, y in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, can be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions x, y are known from U.S. 2018/0074303 A1 .

In each case one of the second facets 23 is assigned to precisely one of the first facets 21 in order to form a respective illumination channel for illuminating the object field 5 . In this way, in particular, lighting can result according to Köhler's principle. The far field is broken down into a large number of object fields 5 with the aid of the first facets 21 . The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to them.

The first facets 21 are each imaged onto the reticle 7 by an associated second facet 23 in a superimposed manner in order to illuminate the object field 5 . In particular, the illumination of the object field 5 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

The illumination of the entrance pupil of the projection optics 10 can be defined geometrically by arranging the second facets 23 . The intensity distribution in the entrance pupil of the projection optics 10 can be set by selecting the illumination channels, in particular the subset of the second facets 23 that guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

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.

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

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

The entrance pupil of the projection optics 10 cannot regularly be illuminated exactly with the second facet mirror 22 . When imaging the projection optics 10, which telecentrically images the center of the second facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found in which the distance between the aperture rays, which is determined in pairs, is minimal. This surface represents the entrance pupil or a surface conjugate to it in position space. In particular, this surface shows a finite curvature.

The projection optics 10 may have different positions of the entrance pupil for the tangential and for the sagittal beam path. In this case, an imaging Ele ment, in particular an optical component of the transmission optics, between the second facet mirror 22 and the reticle 7 are provided. 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.

At the in the 1 shown arrangement of the components of the illumination optics 4, the second facet mirror 22 is arranged in a conjugate to the entrance pupil of the projection optics 10 surface. The first facet mirror 20 is arranged tilted to the object plane 6 . The first facet mirror 20 is tilted relative to an arrangement plane that is defined by the deflection mirror 19 . The first facet mirror 20 is tilted relative to an arrangement plane that is defined by the second facet mirror 22 .

2 shows a schematic view of an embodiment of an optical system 100 for the projection exposure system 1. 3 shows a schematic top view of the optical system 100 2 and 3 referenced at the same time.

The optical system 100 can be a projection optics 4 as explained above or part of such a projection optics 4 . The optical system 100 can therefore also be referred to as projection optics. However, the optical system 100 can also be an illumination system 2 as explained above or part of an illumination system 2 of this type. Therefore, the optical system 100 can alternatively also be referred to as an illumination system. However, it is assumed below that the optical system 100 is a projection optics 4 or part of such a projection optics 4 . The optical system 100 is suitable for EUV lithography. However, the optical system 100 can also be suitable for DUV lithography.

The optical system 100 may include a plurality of optical elements 102, one of which is shown in FIGS 2 and 3 however only one is shown. Therefore, only one optical element 102 will be discussed below. The optical element 102 can be one of the mirrors M1 to M6. The optical element 102 comprises a substrate 104 and an optically active surface 106, for example a mirror surface. The substrate 104 can also be referred to as a mirror substrate. The substrate 104 may comprise glass, ceramic, glass-ceramic, or other suitable material.

The optically effective surface 106 is provided on a front side 108 of the substrate 104 . The optically effective surface 106 can be implemented with the aid of a coating applied to the front side 108 . The optically effective surface 106 is a mirror surface. The optically effective surface 106 is suitable for reflecting illumination radiation 16, in particular EUV radiation, during operation of the optical system 100. The optically effective surface 106 can be viewed in accordance with FIG 3 have an oval or elliptical geometry. The optical element 102 or the substrate 104 can have a triangular geometry. In principle, however, the geometry is arbitrary.

The optical element 102 has a rear side 110 facing away from the optically effective surface 106 or the front side 108 . The back 110 has no defined optical properties. This means in particular that the rear side 110 is not a mirror surface and therefore does not have any reflective properties.

A plurality of mirror sockets 112, 114, 116 are provided on the rear side 110. A first mirror socket 112, a second mirror socket 114 and a third mirror socket 116 are provided. In other words, the optical element 102 includes exactly three mirror sockets 112, 114, 116. The mirror sockets 112, 114, 116 can be of identical geometric design. The mirror bushings 112, 114, 116 are cylindrical and extend in the orientation of 2 underside out of the back 110. The mirror sockets 112, 114, 116 form corners of an imaginary triangle.

The optical element 102 or the optically effective surface 106 has six degrees of freedom, namely three translational degrees of freedom in each case along the first spatial direction or x-direction x, the second spatial direction or y-direction y and the third spatial direction or z-direction z and three rotational degrees of freedom respectively about the x-direction x, the y-direction y and the z-direction z. This means that a position and an orientation of the optical element 102 or of the optically effective surface 106 can be determined or described using the six degrees of freedom.

The "position" of the optical element 102 or the optically effective surface 106 refers in particular to its coordinates or the coordinates of a measuring point provided on the optical element 102 with respect to the x-direction x, the y-direction y and the z-direction z to understand. The “orientation” of the optical element 102 or the optically active surface 106 is to be understood in particular as its or its tilting with respect to the three spatial directions x, y, z. That is, the optical element 102 or the optically effective surface 106 can be tilted about the x-direction x, the y-direction y and/or the z-direction z.

This results in the six degrees of freedom for the position and/or orientation of the optical element 102 or the optically effective surface 106. A “layer” of the optical element 102 or the optically effective surface 106 includes both its position and its orientation . Accordingly, the term "position" can be replaced by the phrase "position and orientation" and vice versa.

In the 2 an actual position IL of the optical element 102 or the optically effective surface 106 is shown with solid lines and a target position SL of the optical element 102 or the optically effective surface 106 is shown with dashed lines and the reference sign 102′ or 106′. The optical element 102 can be moved from its actual position IL to the target position SL and vice versa. For example, the optical element 102 in the target position SL meets certain optical specifications or requirements that the optical element 102 in the actual position IL does not meet.

In order to move the optical element 102 from the actual position IL to the target position SL, the optical system 100 includes an adjustment device 118. The adjustment device 118 is set up to adjust the optical element 102. In the present case, “adjusting” or “aligning” is to be understood in particular as changing the position of the optical element 102 . For example, the optical element 102 can be moved from the actual position IL to the target position SL and vice versa with the aid of the adjustment device 118 . The adjustment or alignment of the optical element 102 can thus take place with the aid of the adjustment device 118 in all six aforementioned degrees of freedom.

The adjustment device 118 includes a plurality of manipulator arrangements 120, 122, 124, which are shown in FIG 2 are only shown very schematically. The manipulator arrangements 120, 122, 124 can also be referred to as actuating element arrangements. A manipulator arrangement 120, 122, 124 is assigned to each mirror socket 112, 114, 116. This means in particular that exactly three manipulator arrangements 120, 122, 124 are provided. Each manipulator arrangement 120, 122, 124 can be assigned two of the aforementioned degrees of freedom. An adjustment of the optical element 102 in all six degrees of freedom is thus possible with the three manipulator arrangements 120, 122, 124.

A first manipulator arrangement 120 is assigned to the first mirror socket 112 . A second manipulator arrangement 122 is assigned to the second mirror socket 114 . A third manipulator arrangement 124 is assigned to the third mirror socket 116 . The manipulator arrangements 120, 122, 124 are constructed identically. In the following, therefore, only the first manipulator arrangement 120 or the first mirror socket 112 will be discussed, which are simply referred to below as the manipulator arrangement 120 or as the mirror socket 112 . All of the following statements relating to the manipulator arrangement 120 can be applied to the manipulator arrangements 122, 124 and vice versa.

The manipulator arrangement 120 is coupled to the mirror socket 112 via a connection point 126 . Furthermore, the manipulator arrangement 120 is coupled to a fixed world 132 via two further connection points 128, 130. Fixed world 132 may be a force frame or other immovable structure.

The manipulator arrangement 120 has two manipulators 134, 136, in particular a first manipulator 134 and a second manipulator 136. The six degrees of freedom of the optical element 102 can be adjusted with the aid of all manipulators 134, 136 of all manipulator arrangements 120, 122, 124. The manipulators 134, 136 can also be referred to as adjusting elements, actuators or actuators. In particular, the manipulators 134, 136 are so-called voice coil manipulators (VCM) or voice coil actuators (VCA) or can be referred to as such.

Both manipulators 134, 136 are connected to the mirror socket 112 at the connection point 126. Furthermore, the manipulators 134, 136 are connected to the fixed world 132 via the connection points 128, 130. The manipulators 134, 136 can be controlled with the aid of a control and regulation unit 138 of the adjustment device 118 in order to adjust the optical element 102. All manipulators 134, 136 of all manipulator arrangements 120, 122, 124 are operatively connected to the control and regulation unit 138, so that the control and regulation unit 138 can adjust the optical element 102 in all six degrees of freedom with the aid of suitable activation of the manipulators 134, 136 . This can be done on the basis of sensor signals from a sensor system, not shown, which can detect the actual position IL and the target position SL of the optical element 102 .

4 shows a schematic sectional view of an embodiment of a first manipulator 134 as mentioned above.

The first manipulator 134 includes a manipulator housing 140 attached to the solid world 132 is bound. For example, the manipulator housing 140 can be connected to the fixed world 132 at the connection point 128 . A magnet assembly 142 is coupled to the manipulator housing 140 via two spring elements 144 , 146 . The spring elements 144, 146 can be leaf springs. The magnet assembly 142 includes a tubular magnet assembly housing and a magnet attached to the outside of the magnet assembly housing. The magnet can be a permanent magnet. The magnet assembly housing is connected to the manipulator housing 140 by means of the spring elements 144,146. The optical element 102 is coupled to the magnet assembly 142 by means of a spring element 148 .

An annular coil assembly 152 encircles the magnet assembly housing. The magnet assembly housing is thus passed through the coil assembly 152 . The coil assembly 152 includes a coil and a reaction mass, as discussed below. The coil assembly 152 can move relative to the magnet assembly housing or vice versa. A manipulator pin is connected to the magnet assembly housing, which in turn is coupled to the mirror socket 112 via the connection point 126 . The manipulator pin lies obliquely in a plane spanned by the y-direction y and the z-direction z. In particular, the manipulator pin is inclined to the y-direction y and the z-direction z. In particular, the manipulator pin is inclined at an angle of inclination α relative to the z-direction z. The angle of inclination α can be 60°.

The coil assembly 152 is connected to the manipulator housing 140 with the aid of a spring element 156 . Furthermore, the coil assembly 152 is coupled to the manipulator housing 140 by means of a damper 158 . The damper 158 can be implemented by an eddy current brake. The coil assembly 152, the spring element 156 and the damper 158 form a spring-mass-damper system 160 of the first manipulator 134.

When the first manipulator 134 is in operation, Lorentz forces act between the coil assembly 152 and the magnet assembly 142 , as indicated by an arrow 162 . The manipulator pin connected to the magnet assembly housing thereby moves in a first direction of movement 164. The first direction of movement 164 is arranged in the plane spanned by the y-direction y and the z-direction z and at an angle to the y-direction y and the z-direction z oriented. The first direction of movement 164 runs along the manipulator pin.

5 shows a schematic sectional view of an embodiment of a second manipulator 136 as mentioned above.

The second manipulator 136 includes a manipulator housing 166 tethered to the fixed world 132 . For example, the manipulator housing 166 can be attached to the fixed world 132 at the attachment point 130 . A magnet assembly 168 is coupled to a coil assembly 178 via a spring member 170 . The coil assembly 178 includes a coil and a reaction mass as discussed below. The spring element 170 can be a leaf spring. The magnet assembly 168 includes a tubular magnet assembly housing and a magnet attached to the outside of the magnet assembly housing. The magnet can be a permanent magnet. The magnet assembly housing is connected to the coil assembly 178 by means of the spring element 170 . The magnet assembly 168 is connected to the optical element 102 by means of a spring element 180 .

The coil assembly 178 encircles the magnet assembly housing. The magnet assembly housing is thus passed through the coil assembly 178 . The coil assembly 178 can move relative to the magnet assembly housing or vice versa. A manipulator pin is connected to the magnet assembly housing, which in turn is coupled to the mirror socket 112 via the connection point 126 . The manipulator pin runs along the z-direction z.

The coil assembly 178 is connected to the manipulator housing 166 with the aid of a spring element 186 . Furthermore, the coil assembly 178 is coupled to the manipulator housing 166 by means of a damper 190 . The damper 190 can be implemented by an eddy current brake. The coil assembly 178, the spring element 186 and the damper 190 form a spring-mass-damper system 194 of the second manipulator 136.

When the second manipulator 136 is in operation, Lorentz forces act between the coil assembly 178 and the magnet assembly 168 , as indicated by an arrow 196 . As a result, the manipulator pin connected to the magnet assembly housing moves in a second direction of movement 198 which differs from the first direction of movement 164 of the manipulator pin of the first manipulator 134 . The second direction of movement 198 is oriented along the z-direction z. The second direction of movement 198 runs along the manipulator pin.

During exposure operation, the optical element 102 on the manipulator arrangements 120, 122, 124 or on the manipulators 134, 136 is decoupled from the solid world 132 via the respective spring-mass-damper system 160, 194, which is interposed as a low-pass filter. This is to prevent the transmission of high frequency vibrations to the solid world 132 and/or a sensor frame. Here, the natural frequency ω of the respective spring-mass-damper system 160, 194 is particularly important and specified. However, the required natural frequency ω cannot always be met in the specification due to complex process fluctuations and/or production fluctuations. This can lead to a costly and time-consuming rework process. This needs to be improved.

The main influencing factor for the natural frequency ω is the stiffness c and the mass m of the entire spring-mass-damper system 160, 194. The following then applies: $$\omega =\sqrt{\frac{c}{m}}$$

Since the adjustment of the rigidity c cannot be implemented or can only be implemented with great effort for process reasons, such as installation space, cleaning, cleanliness or the like, in terms of costs and/or benefits, the natural frequency ω is present by varying the reaction masses of the coil assemblies 152 , 178 adjusted.

Now returning to that 4 the coil assembly 152 includes a coil disposed adjacent the magnet and a reaction mass. Different mass elements 206 can be attached to the reaction mass with the aid of a fastening element in order to change the mass m of the spring-mass-damper system 160 and thus its natural frequency ω.

The fastener can be a screw. The mass element 206 can be plate-shaped or disk-shaped. For example, several mass elements 206 with an identical mass can be attached to the reaction mass. Alternatively, a modular system with mass elements 206 of different masses can also be kept available, from which a mass element 206 with a suitable mass is then selected in order to obtain the desired natural frequency ω.

Now returning to that 5 the coil assembly 178 includes a coil disposed adjacent the magnet and a reaction mass. Different mass elements 214 can be attached to the reaction mass with the aid of a fastening element in order to change the mass m of the spring-mass-damper system 194 and thus its natural frequency ω.

The fastener can be a screw. The mass element 214 can be plate-shaped or disk-shaped. For example, several mass elements 214 with an identical mass can be attached to the reaction mass. Alternatively, a modular system with mass elements 214 of different masses can also be kept available, from which a mass element 214 with a suitable mass is then selected in order to obtain the desired natural frequency ω.

6 shows a schematic block diagram of an embodiment of a method for adjusting the natural frequency of the manipulator 134, 136.

A desired natural frequency ω of the respective spring-damper-mass system 160, 194 of 85 Hz is specified, for example. In a step S1, a central mass element 206, 214 is mounted on the respective reaction mass. An input measurement then takes place in a step S2. The input measurement can be used to assess whether the natural frequency ω is within an allowable specification, above specification, or below specification.

If the achieved natural frequency ω is within the specification, the manipulator 134, 136 can be integrated into the optical system 100 in a step S3.

If the achieved natural frequency ω is above the specification, a mass element 206, 214 with a higher mass or an additional mass element 206, 214 can be mounted on the respective reaction mass in a step S4. Step S2 is then carried out again. Depending on whether the achieved natural frequency ω is then within the specification or not, either step S3 or step S4 can be carried out again. Steps S2 and S4 are carried out iteratively until the natural frequency ω is within the specification and the manipulator 134, 136 can be integrated into the optical system 100 in step S3.

If the achieved natural frequency ω is below the specification, a mass element 206, 214 with a smaller mass can be mounted on the respective reaction mass in a step S5. Step S2 is then carried out again. Depending on whether the achieved natural frequency ω is then within the specification or not, either step S3 or step S5 can be carried out again. Steps S2 and S5 become carried out iteratively until the natural frequency ω is within the specification and the manipulator 134, 136 can be integrated into the optical system 100 in step S3.

7 shows a schematic block diagram of a further embodiment of a method for adjusting the natural frequency of the manipulator 134, 136.

The procedure according to 7 is preferably part of the method according to 6 or the other way around. The method includes a step S10 of detecting the natural frequency ω of the manipulator 134, 136. A suitable measuring device can be provided for this purpose. In a step S20, it is detected or determined whether the detected natural frequency ω is within or outside of a specified specification.

In a step S30, the mass element 206, 214 of the respective coil assembly 152, 178 is exchanged or replaced if the detected natural frequency ω is outside of the specified specification. According to a step S40, steps S10 to S30 are repeated iteratively until the detected natural frequency ω is within the specified specification. After step S40, the manipulator 134, 136 is integrated or built into the optical system 100.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

Reference List

1

projection exposure system

2

lighting system

3

light source

4

lighting optics

5

object field

6

object level

7

reticle

8th

reticle holder

9

reticle displacement drive

10

projection optics

11

image field

12

picture plane

13

wafers

14

wafer holder

15

Wafer displacement drive

16

illumination radiation

17

collector

18

intermediate focal plane

19

deflection mirror

20

first facet mirror

21

first facet

22

second facet mirror

23

second facet

100

optical system

102

optical element

102'

optical element

104

substrate

106

optically effective surface

106'

optically effective surface

108

front

110

back

112

mirror socket

114

mirror socket

116

mirror socket

118

adjustment device

120

manipulator assembly

122

manipulator assembly

124

manipulator arrangement

126

connection point

128

connection point

130

connection point

132

solid world

134

manipulator

136

manipulator

138

control and regulation unit

140

manipulator body

142

magnet assembly

144

spring element

146

spring element

148

spring element

152

coil assembly

156

spring element

158

mute

160

Spring-mass damper system

162

Arrow

164

direction of movement

166

manipulator body

168

magnet assembly

170

spring element

178

coil assembly

180

spring element

186

spring element

190

mute

194

Spring-mass damper system

196

Arrow

198

direction of movement

206

mass element

214

mass element

IL

actual situation

M1

mirror

M2

mirror

M3

mirror

M4

mirror

M5

mirror

M6

mirror

SL

target position

S1

Step

S2

Step

S3

Step

S4

Step

S5

Step

S10

Step

S20

Step

S30

Step

S40

Step

x

x direction

y

y direction

e.g

z direction

a

tilt angle

QUOTES INCLUDED IN DESCRIPTION

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

Patent Literature Cited

• DE 102008009600 A1 [0062, 0066]
• US20060132747A1 [0064]
• EP 1614008 B1 [0064]
• US6573978 [0064]
• DE 102017220586 A1 [0069]
• US 20180074303 A1 [0083]

Claims (15)

Manipulator (134, 136) for adjusting an optical element (102, 102'), having a magnet assembly (142, 168) couplable to the optical element (102, 102'), and a coil assembly (152, 178) that is linearly displaceable by means of the magnet assembly (142, 168) to adjust the optical element (102, 102'), wherein the coil assembly (152, 178) has an exchangeable mass element (206, 214) for adjusting the natural frequency of the manipulator (134, 136). manipulator after claim 1 wherein the coil assembly (152, 178) includes a reaction mass, and wherein the mass member (206, 214) is releasably attached to the reaction mass. manipulator after claim 1 or 2 , wherein the coil assembly (152, 178) is coupled to a manipulator housing (140, 166) of the manipulator (134, 136) by means of a spring element (156, 186) and by means of a damper (158, 190). manipulator after claim 3 , wherein the damper (158, 190) has an eddy current brake. manipulator after claim 3 or 4 , wherein the magnet assembly (142) is coupled to the manipulator housing (140) by means of spring elements (144, 146). manipulator after one of the Claims 1 - 4 , wherein the magnet assembly (168) is coupled to the coil assembly (178) by means of spring elements (170). manipulator after one of the Claims 1 - 6 , further comprising a manipulator pin, which is passed through the magnet assembly (142, 168) at least in sections, wherein the magnet assembly (142, 168) can be coupled to the optical element (102, 102') with the aid of the manipulator pin. manipulator after one of the Claims 1 - 7 , wherein the magnet assembly (142, 168) is passed through the coil assembly (152, 178) at least in sections. Optical system (100) for a projection exposure system (1), having an optical element (102, 102 '), and a manipulator (134, 136) according to one of Claims 1 - 8th wherein the magnet assembly (142, 168) is coupled to the optical element (102, 102'). Optical system after claim 9 , further comprising a first manipulator (134) and a second manipulator (136), wherein the first manipulator (134) and the second manipulator (136) together form a manipulator arrangement (120, 122, 124) of the optical system (100). Optical system after claim 10 , wherein a first direction of movement (164) of the first manipulator (134) is oriented obliquely to a second direction of movement (198) of the second manipulator (136). Optical system after claim 10 or 11 , further comprising a first manipulator arrangement (120), a second manipulator arrangement (122) and a third manipulator arrangement (124), wherein the optical element (102, 102') can be adjusted in six degrees of freedom in order to move the optical element (102, 102') to spend from an actual position (IL) in a target position (SL) and vice versa, and each manipulator arrangement (120, 122, 124) are assigned two of the six degrees of freedom. Projection exposure system (1) with a manipulator (134, 136) according to one of Claims 1 - 8th and / or an optical system (100) according to one of claims 9 - 12 . Method for adjusting the natural frequency of a manipulator (134, 136) for adjusting an optical element (102, 102'), the manipulator (134, 136) having a magnet assembly (142, 168) which can be coupled to the optical element (102, 102'). and a coil assembly (152, 178) linearly displaceable by means of the magnet assembly (142, 168) to adjust the optical element (102, 102'), comprising the steps of: a) detecting (S10) a natural frequency (ω) of the manipulator (134, 136), b) determining (S20) whether the detected natural frequency (ω) is within or outside of a specified specification, c) replacing (S30) a mass element (206, 214) of the coil assembly (152, 178) if the detected natural frequency (ω) is outside of the predetermined specification, and d) repeating (S40) steps a) to c) until the detected natural frequency (ω) is within the predetermined specification. procedure after Claim 14 , wherein the manipulator (134, 136) after step d) is integrated into an optical system (100) which has the optical element (102, 102').

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