Individual mirror for a faceted mirror of an illumination optical unit of a projection exposure system

Abstract

The invention relates to a pivotally mounted individual mirror (20) for a faceted mirror (13; 14) of an illumination optical unit (4) of a projection exposure system (1), having a direction-based pivoting range.

Description

[0001] Single mirror for a facet mirror of an illumination optics of a projection exposure system

[0002] This patent application claims priority from German patent application DE 10 2023 203 810.2, the contents of which are incorporated herein by reference.

[0003] The invention relates to a single mirror for a facet mirror, in particular a field facet mirror or a pupil facet mirror, of an illumination optics system of a projection exposure system for microlithography. The invention further relates to a facet mirror, in particular a field facet mirror or a pupil facet mirror, for an illumination optics system of a projection exposure system, as well as to an illumination optics system and an illumination system comprising such a facet mirror. Furthermore, the invention relates to an optical system for a projection exposure system comprising such a facet mirror, as well as to a corresponding projection exposure system. Finally, the invention relates to a method for producing a micro- or nanostructured component, as well as to a component produced according to the method.

[0004] A mirror array with a plurality of movable individual mirrors is known, for example, from WO 2010 / 049 076 A2. Actuators are provided for moving the individual mirrors.

[0005] It is an object of the present invention to improve a displaceable individual mirror for a facet mirror of an illumination optics system of a projection exposure system for microlithography, as well as assemblies and subsystems of a corresponding projection exposure system having one or more such individual mirrors. This object is achieved by the subject matter of the independent claims.

[0006] A core of the invention is to design a single mirror with a suspension for pivotably supporting its mirror body with two degrees of freedom of tilt and an actuator device for pivoting the mirror body such that the mirror body has a direction-dependent tilt angle range. For this purpose, the suspension and / or the actuator device can, in particular, have direction-dependent properties. The terms "direction-dependent" and "non-isotropic" refer here and below to the azimuthal tilt direction.

[0007] This allows the individual mirror to be specifically adapted to specific requirements. This allows certain properties of the individual mirror to be improved, particularly its thermal resistance.

[0008] According to the invention, it was recognized that the requirement for the maximum tilting range for two tilting axes, which in particular can be perpendicular to one another, is often different.

[0009] The tilt angles or the tilt angle range can be the maximum achievable tilt angles of the individual mirror, the tilt angles that can be generated by applying a certain force or torque, or the tilt angles that can actually be generated by means of the actuator device.

[0010] In particular, the tilt angle range may not be isotropic. In particular, the maximum possible tilt angle, in particular the maximum tilt angle that can be generated by applying a specific force to the mirror body, and / or the maximum tilt angle that can be generated by the actuator device, may be direction-dependent.

[0011] The tilt angle range can, in particular, be elliptical. This means that a curve that represents the required two-dimensional tilt angle range of the individual mirror or a curve that represents the actual two-dimensional tilt angle range of the individual mirror, in particular when subjected to a specific force or when subjected to the maximum force or torque that can be generated by the actuator device, has an elliptical shape, or at least a first approximation.

[0012] The tilt angle range can be direction-dependent, asymmetrical, such that the ratio of the tilt angles about two pivot axes of the individual mirror, in particular two pivot axes defined by the suspension of the individual mirror, in particular perpendicular to one another, is at least 1.05, in particular at least 1.1, in particular at least 1.2, in particular at least 1.3.

[0013] According to one aspect, the suspension is designed such that the stiffness of the suspension with respect to pivoting the mirror body about a first pivot axis is greater than the stiffness of the suspension with respect to pivoting the mirror body about a second pivot axis. The second pivot axis can, in particular, be oriented perpendicular to the first pivot axis. It can also enclose an angle of 60° with the first pivot axis.

[0014] The stiffness of the suspension with respect to pivoting of the mirror body about a first pivot axis can in particular be at least 3%, in particular at least 5%, in particular at least 10%, in particular at least 20%, in particular at least 30% greater than the stiffness of the suspension with respect to pivoting of the mirror body about the second pivot axis.

[0015] In one aspect, the suspension may include springs of different stiffness.

[0016] When different sizes are mentioned in this application, these sizes may differ from each other by at least 3%, in particular at least 5%, in particular at least 10%, in particular at least 20%, in particular at least 30%. The relative difference is usually less than an order of magnitude, in particular less than a factor of 10, in particular less than a factor of 5, in particular less than a factor of 3.

[0017] The springs can be torsion springs and / or leaf springs.

[0018] In particular, the springs can have different widths and / or different thicknesses and / or different lengths. This allows the mechanical, thermal, and electrical properties of the springs to be easily influenced.

[0019] According to one aspect, the suspension comprises springs made of different materials

[0020] In particular, it is possible to form a first spring from a first material and a second spring from a second material, wherein the first material and the second material are not identical.

[0021] The choice of material can influence the mechanical and thermal properties of the springs.

[0022] According to one aspect of the invention, at least one spring element which is assigned to an axle with a lower tilt angle requirement, in particular all such spring elements, is formed from a material with a higher shear modulus and / or a higher elastic modulus and / or a simultaneously higher thermal conductivity and / or a higher electrical conductivity than at least one spring element, in particular all spring elements which are assigned to an axle with a higher tilt angle requirement.

[0023] According to a further aspect, the suspension has springs with different coatings.

[0024] A coating can influence the mechanical and / or thermal properties of the springs. Different coatings mean that a first spring has a first coating and a second spring has a second coating, whereby the first coating is not identical to the second coating. The difference can lie in the material of the coating and / or in the details of its application. Different coatings also mean that one spring has a coating and another spring has no coating.

[0025] According to a further aspect, the actuator device is designed such that the maximum torque acting on the mirror body that can be generated by means of the actuator device is greater with respect to a first pivot axis than with respect to a second pivot axis.

[0026] Regarding the differences, please refer to the previous description.

[0027] The pivot axes can be perpendicular to each other. They can also form an angle of 60° between them. These specifications are not to be understood as limiting.

[0028] It was recognized that a reduction of the maximum torque that can be generated can lead to a simplification in terms of the design of the actuator device.

[0029] According to a further aspect, the actuator device comprises actuator elements arranged in such a way that they exhibit an uneven distribution. This also allows a direction-dependent maximum torque to be achieved.

[0030] Electrodes, especially in the form of combs, serve as actuator elements. The electrodes can be arranged in a circular ring-shaped region. They can extend radially to a central axis, in particular through the intersection of the pivot axes of the mirror body.

[0031] The actuator elements, in particular the electrodes, can in particular have a different angular distribution.

[0032] The actuator elements, in particular the electrodes, can in particular have different, i.e., azimuthally varying, spacings. This is understood in particular to mean that there are at least two pairs of adjacent actuator elements, in particular electrodes, which have different spacings.

[0033] According to a further aspect, the actuator device has differently designed actuator elements.

[0034] The actuator device can in particular have electrodes, in particular comb fingers, with different lengths and / or different heights and / or different geometries.

[0035] This allows the torque that can be generated by the actuator device to be influenced. According to a further aspect, the actuator device has a different number of actuator elements, in particular electrodes, in particular comb fingers, for different pivoting directions.

[0036] For example, the number of comb fingers assigned to a first pivot axis may be at least 2, in particular at least 5, in particular at least 10 greater than the number of comb fingers assigned to a second pivot axis.

[0037] The actuator elements, especially the electrodes, especially the comb fingers, can be evenly distributed, equidistantly arranged. They can also be unevenly distributed.

[0038] According to a further aspect, the actuator device and the suspension are adapted to each other.

[0039] For example, the maximum torque that can be generated by the actuator device in a certain direction can be adapted to the stiffness of the suspension and the required maximum tilt angle in this direction.

[0040] According to a further aspect, the single mirror can be designed as a microelectromechanical system (MEMS) or a microoptoelectromechanical system (MOEMS).

[0041] The individual mirror can be designed in particular as a micromirror. It can have a reflection surface of at most 1 mm 2The individual mirror may have a reflection surface with a maximum side length or a maximum diameter of at most 2 mm, in particular at most 1 mm, in particular at most 600 pm, in particular at most 400 pm.

[0042] The reflecting surface of the individual mirror can be polygonal, particularly regular. The reflecting surface of the individual mirror can also be formed as a non-regular polygon.

[0043] The reflection surface of the individual mirror can be triangular, square or hexagonal.

[0044] The reflection surface of the individual mirror can preferably be tiled. This means that the reflection surface of the individual mirror is designed in such a way that it enables a substantially seamless tiling of a plane.

[0045] According to a further aspect, the individual mirror can be constructed according to the shadow-casting principle. This means that the electrical, electronic, and mechanical components of the individual mirror are arranged in a cylindrical volume, wherein the reflective surface of the individual mirror forms a directrix of this cylindrical volume. It can be an oblique cylinder. It is preferably a vertical cylinder. The volume can, in particular, be a prism-shaped, in particular a cuboid-shaped volume. According to a further aspect, it can be provided to combine a plurality of individual mirrors to form a mirror module. The mirror module can, in particular, be a mechanical unit.

[0046] This can facilitate handling of the individual mirrors, especially when a large number of them are involved. In these mirror modules, the substructure, which contains the common electronics and cooling system, can have a cylindrical shape with a relatively large height-to-aspect ratio.

[0047] Regarding the details of the actuator and / or sensor device, in particular its electrodes, reference is made to DE 10 2015 204 874 A1.

[0048] The invention also relates to a facet mirror for an illumination optics system of a projection exposure system comprising a plurality of individual mirrors, wherein at least a non-empty subset of the individual mirrors is configured according to the preceding description. In particular, at least 10%, in particular at least 20%, in particular at least 30%, in particular at least 50%, in particular at least 70%, in particular all of the individual mirrors can be configured according to the preceding description.

[0049] The directional dependence of the tilt angle ranges of the individual mirrors can be organized in groups. In particular, it can be identical in groups. This means that groups of individual mirrors have the same directional dependence. The individual mirrors of a group are arranged in a simply connected region, wherein in particular no mirrors are arranged in this region that do not belong to this group. The directional dependence of the individual mirrors can also vary systematically across the entire extension of the facet mirror. In particular, it can be represented as a function of the position of the individual mirror on the facet mirror. This can in particular be a continuous, in particular a differentiable function.

[0050] It is also possible to individually select the tilt angle range of the individual mirrors, in particular its direction dependence, for at least a subset of the individual mirrors, in particular for all of the individual mirrors.

[0051] The facet mirror can be a field facet mirror or a pupil facet mirror. The facet mirror can also be arranged in a plane that is neither conjugated to a field plane nor to a pupil plane.

[0052] According to a further aspect, at least two of the individual mirrors, in particular at least two different groups of the individual mirrors, have different pre-tilts.

[0053] This allows asymmetric tilt angle requirements to be met.

[0054] Different pre-tilts are understood in particular to mean that the normals to the reflecting surfaces of the individual mirrors, in particular the surface normals, pass through a central point of the reflecting surface of the individual mirrors, and in the neutral, untilted state of the latter, have different orientations. The individual mirrors can in particular be arranged in groups on supports. By tilting such a support, a group-wise pre-tilt of the individual mirrors can be achieved in a simple manner. A pre-tilt of the reflecting mirror surface can also be realized using a wedge-shaped mirror body.

[0055] The pre-tilt of the individual mirrors can preferably be adjustable.

[0056] In particular, it is possible to make the tilt of the support for the individual mirrors adjustable, in particular mechanically adjustable.

[0057] The invention also relates to an illumination optics for a projection exposure system with at least one, in particular two facet mirrors, according to the preceding description.

[0058] Such lighting optics enable particularly flexible adjustment of different lighting settings.

[0059] The invention further relates to an illumination system for a projection exposure system, including such an illumination optics and a radiation source for generating illumination radiation. The radiation source can, in particular, be an EUV radiation source for generating illumination radiation in the EUV range.

[0060] The invention further relates to an optical system for a projection exposure apparatus comprising an illumination optical system according to the preceding description and a projection optical system for imaging a reticle arranged in an object field onto a wafer arranged in an image field.

[0061] Furthermore, the invention relates to a projection exposure system for microlithography with such an optical system and a radiation source for generating illumination radiation, in particular in the EUV range.

[0062] Finally, the invention relates to a method for producing a micro- or nano-structured component and to a component produced according to the method.

[0063] By providing a projection exposure system according to the preceding description, a corresponding method and the components produced thereby are improved.

[0064] Further advantages, details, and particulars of the invention will become apparent from the description of exemplary embodiments based on the drawings. They show:

[0065] Fig. 1 is a schematic representation of a projection exposure system and its components,

[0066] Fig. 2 schematically shows a cross section through a displaceable

[0067] Single mirror, Fig. 3 partial representation of a single mirror with components of an actuator device for moving the single mirror,

[0068] Fig. 5 shows a schematic plan view of a part of the actuator

[0069] Electrodes for moving a single mirror,

[0070] Fig. 6 schematically shows a view according to Fig. 5 of an alternative

[0071] Arrangement of the actuator electrodes,

[0072] Fig. 7 schematically shows another variant of the arrangement of the actuator electrodes,

[0073] Fig. 8 shows an example of an embodiment of a

[0074] Solid-state joint for tiltable mounting of a single mirror and

[0075] Fig. 9 schematically shows a variant of the solid body joint according to

[0076] Fig. 8.

[0077] First, the general structure of a projection exposure system 1 and its components are described. For details in this regard, reference is made to WO 2010 / 049 076 A2, which is hereby fully incorporated into the present application as a component thereof. The description of the general structure of the projection exposure system 1 is to be understood solely as an example. It serves to explain a possible application of the subject matter of the present invention. The subject matter of the present invention can also be used in other optical systems, in particular in alternative variants of projection exposure systems. The tilting mirror concept described below is in particular not limited to the structure of the projection exposure system 1 or its components shown as an example. Its application is in particular not limited to the specific MEMS design shown as an example in this context.

[0078] Fig. 1 shows a schematic meridional section of a projection exposure system 1 for microlithography. An illumination system 2 of the projection exposure system 1 has, in addition to a radiation source 3, illumination optics 4 for exposing an object field 5 in an object plane 6. The object field 5 can be rectangular or arc-shaped with an x / y aspect ratio of, for example, 13 / 1. A reflective reticle (not shown in Fig. 1) arranged in the object field 5 is exposed, which carries a structure to be projected with the projection exposure system 1 for producing micro- or nano-structured semiconductor components. Projection optics 7 serve to image the object field 5 into an image field 8 in an image plane 9. The structure on the reticle is imaged onto a light-sensitive layer of a wafer (not shown in the drawing) arranged in the region of the image field 8 in the image plane 9.

[0079] The reticle, which is held by a reticle holder (not shown), and the wafer, which is held by a wafer holder (not shown), are scanned synchronously in the y-direction during operation of the projection exposure system 1. Depending on the image scale of the projection optics 7, counter-scanning of the reticle relative to the wafer can also take place. The radiation source 3 is an EUV radiation source with emitted useful radiation in the range between 5 nm and 30 nm. This can be a plasma source, for example a GDPP source (Gas Discharge Produced Plasma) or an LPP source (Laser Produced Plasma). Other EUV radiation sources, for example those based on a synchrotron or a free electron laser (FEL), are also possible.

[0080] EUV radiation 10 emanating from the radiation source 3 is focused by a collector 11. A corresponding collector is known, for example, from EP 1 225 481 A2. After the collector 11, the EUV radiation 10 propagates through an intermediate focal plane 12 before impinging on a field facet mirror 13. The field facet mirror 13 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6. The field facet mirror 13 can be arranged at a distance from a plane conjugated to the object plane 6. In this case, it is generally referred to as the first facet mirror.

[0081] The EUV radiation 10 is also referred to below as useful radiation, illumination radiation or imaging light.

[0082] After the field facet mirror 13, the EUV radiation 10 is reflected by a pupil facet mirror 14. The pupil facet mirror 14 lies either in the entrance pupil plane of the projection optics 7 or in a plane optically conjugate thereto. It can also be arranged at a distance from such a plane. The field facet mirror 13 and the pupil facet mirror 14 are constructed from a plurality of individual mirrors, which are described in more detail below. The subdivision of the field facet mirror can

[0083] 13 into individual mirrors such that each of the field facets, which individually illuminate the entire object field 5, is represented by exactly one of the individual mirrors. Alternatively, it is possible to construct at least some or all of the field facets by a plurality of such individual mirrors. The same applies to the design of the pupil facets of the pupil facet mirror 14 assigned to the field facets, which can each be formed by a single individual mirror or by a plurality of such individual mirrors.

[0084] The EUV radiation 10 strikes the two facet mirrors 13, 14 at a defined angle of incidence. The two facet mirrors are exposed to the EUV radiation 10 particularly in the range of normal incidence operation, i.e., at an angle of incidence less than or equal to 25° to the mirror normal. Exposure at grazing incidence is also possible. The pupil facet mirror 14 is arranged in a plane of the illumination optics 4, which represents a pupil plane of the projection optics 7 or is optically conjugated to a pupil plane of the projection optics 7. Using the pupil facet mirror

[0085] 14 and - optionally - an imaging optical assembly in the form of a transmission optics 15 with mirrors 16, 17, and 18 designated in the order of the beam path for the EUV radiation 10, the field facets of the field facet mirror 13 are imaged superimposed onto the object field 5. The last mirror 18 of the transmission optics 15 is a grazing incidence mirror. The transmission optics 15, together with the pupil facet mirror 14, is also referred to as a follow-up optics for transferring the EUV radiation 10 from the field facet mirror 13 to the object field 5. The illumination light 10 is guided from the radiation source 3 to the object field 5 via a plurality of illumination channels. Each of these illumination channels is assigned a field facet of the field facet mirror 13 and a pupil facet of the pupil facet mirror 14 arranged downstream of this.The individual mirrors of the field facet mirror 13 and the pupil facet mirror 14 can be tilted by actuators, allowing a change in the assignment of the pupil facets to the field facets and, accordingly, a modified configuration of the illumination channels. This results in different illumination settings that differ in the distribution of the illumination angles of the illumination light 10 across the object field 5.

[0086] Different illumination settings can be achieved by tilting the individual mirrors of the field facet mirror 13 and correspondingly changing the assignment of these individual mirrors of the field facet mirror 13 to the individual mirrors of the pupil facet mirror 14. Depending on the tilt of the individual mirrors of the field facet mirror 13, the individual mirrors of the pupil facet mirror 14 newly assigned to these individual mirrors are adjusted by tilting in such a way that, in turn, an image of the field facets of the field facet mirror 13 into the object field 5 is ensured.

[0087] Further aspects of the illumination optics 4 are described below.

[0088] One field facet mirror 13 in the form of a multi- or micro-mirror array (MMA) is an example of an optical assembly for guiding the useful radiation 10, i.e., the EUV radiation beam. The field facet mirror 13 is designed as a microelectromechanical system (MEMS). It has a plurality of individual mirrors 20 arranged in a matrix-like manner in rows and columns in a mirror array. The mirror arrays are modular in design. They can be arranged on a support structure designed as a base plate. Essentially any number of the mirror arrays can be arranged next to one another. The total reflection surface, which is formed by the entirety of all mirror arrays, in particular their individual mirrors 20, can thus be expanded as desired. The mirror arrays are designed in particular in such a way that they enable essentially gapless tiling of a plane.The ratio of the sum of the reflection surfaces 26 of the individual mirrors 20 to the total area covered by the mirror arrays is also referred to as the integration density. This integration density is, in particular, at least 0.5, in particular at least 0.6, in particular at least 0.7, in particular at least 0.8, in particular at least 0.9.

[0089] The individual mirrors 20 are designed to be tiltable by actuators. For details, reference is made, for example, to WO 2012 / 130 768 A2. In total, the field facet mirror 13 has approximately 100,000 individual mirrors 20. Depending on the size of the individual mirrors 20, the field facet mirror 13 can also have a different number of individual mirrors 20. The number of individual mirrors 20 of the field facet mirror 13 is in particular at least 1,000, in particular at least 5,000, in particular at least 10,000. It can be up to 100,000, in particular up to 300,000, in particular up to 500,000, in particular up to 1,000,000. A spectral filter can be arranged in front of the field facet mirror 13, which separates the useful radiation 10 from other wavelength components of the emission of the radiation source 3 that cannot be used for projection exposure. The spectral filter is not shown.

[0090] The entire individual mirror array of the facet mirror 13 has, for example, a diameter of 500 mm and is densely packed with the individual mirrors 20. The individual mirrors 20 represent, up to a scaling factor, the shape of the object field 5, provided that a field facet is realized by exactly one individual mirror. The facet mirror 13 can be formed from 500 individual mirrors 20, each representing a field facet, with a dimension of approximately 5 mm in the y-direction and 100 mm in the x-direction. As an alternative to realizing each field facet by exactly one individual mirror 20, each of the field facets can be approximated by groups of smaller individual mirrors 20, in particular micromirrors. A field facet with dimensions of 5 mm in the y-direction and 100 mm in the x-direction can, for example,using a 1 x 20 array of individual mirrors 20 with dimensions of 5 mm x 5 mm up to a 10 x 200 array of individual mirrors 20 with dimensions of 0.5 mm x 0.5 mm.

[0091] To change the illumination settings, the tilt angles of the individual mirrors 20 are adjusted. The tilt angles have a displacement range of ± 50 mrad, in particular ± 100 mrad, especially ± 200 mrad. When adjusting the tilt position of the individual mirrors 20, an accuracy of better than 0.2 mrad, in particular better than 0.1 mrad, is achieved. The individual mirrors 20 of the field facet mirror 13 and the pupil facet mirror 14 in the embodiment of the illumination optics 4 according to Fig. 1 have multilayer coatings to optimize their reflectivity at the wavelength of the useful radiation 10. This is achieved by a suitable structure of the individual mirrors 20. For details, reference is made to DE 10 2013 206 529 A1, which is hereby fully incorporated into the present application.

[0092] The individual mirrors 20 of the illumination optics 4 are housed in an evacuable chamber 21, of which a boundary wall 22 is indicated in Fig. 1. The chamber 21 communicates with a vacuum pump 25 via a fluid line 23, in which a shut-off valve 24 is housed. The operating pressure in the evacuable chamber 21 is a few Pascals.

[0093] The mirror comprising the plurality of individual mirrors 20, together with the evacuable chamber 21, forms an optical assembly for guiding and / or shaping a beam of EUV radiation 10.

[0094] Each of the individual mirrors 20 can have a reflection surface 26 with dimensions of 0.1 mm x 0.1 mm, 0.5 mm x 0.5 mm, 0.6 mm x 0.6 mm, or even up to 5 mm x 5 mm and larger. The reflection surface 26 can also have smaller dimensions. In particular, it has side lengths in the pm or lower mm range. The individual mirrors 20 are therefore also referred to as micromirrors.

[0095] The reflection surface 26 is part of a mirror body 27 of the individual mirror 20. The mirror body 27 bears the multilayer coating. The mirror body 27 can be made, in particular, of a semiconductor material, in particular silicon, or a semiconductor compound, in particular a silicon compound.

[0096] With the aid of the projection exposure system 1, at least a portion of the reticle is imaged onto a region of a light-sensitive layer on the wafer for the lithographic production of a micro- or nanostructured component, in particular a semiconductor component, e.g., a microchip. Depending on whether the projection exposure system 1 is configured as a scanner or a stepper, the reticle and the wafer are moved in the y-direction in a temporally synchronized manner, either continuously in scanner mode or stepwise in stepper mode.

[0097] Further details and aspects of the mirror arrays 19, in particular the optical components comprising the individual mirrors 20, are described below.

[0098] Fig. 2 shows schematically the structure, in particular the mounting, of the individual mirror 20.

[0099] The mirror body 27 is mounted on a support 32 by means of a suspension 31. The support 32 is also referred to as a substrate or support plate.

[0100] An actuator device 33 and a sensor device 34 are arranged in the area behind the mirror body 27, in particular in the area between the mirror body 27 and the support 32. The individual mirror 20 can be displaced, in particular tilted, by means of the actuator device 33. It can be tilted, in particular, about two tilt axes 35, 36. The individual mirror 20 has, in particular, two degrees of freedom for tilting. The individual mirror 20 can be tilted, in particular, in a controlled, in particular regulated manner.

[0101] For exemplary details of the mounting of the individual mirror 20, reference is made to DE 10 2015 204 874 Al.

[0102] In addition to the mechanical mounting of the individual mirror 20, the suspension 31 serves to dissipate a thermal load resulting from the incident EUV radiation 10, in particular to the carrier 32.

[0103] The suspension 31 can also be used to establish an electrically conductive connection between the mirror body 27 and / or sensors and / or actuators above the suspension 31 and an electrical contact below the suspension, particularly in the region of the support 32. According to the invention, it was recognized that a design of the suspension 31 in which the direction-dependent requirements for the tilt angle range are exploited in such a way that the thermal and electrical resistance are reduced as much as possible leads to advantages.

[0104] Furthermore, it may be provided to adapt the actuator device 33 and the design of the suspension 31. This is particularly advantageous in the case of a radial comb electrode tilt actuator, as described in more detail below.

[0105] Preferably, the actuator device 33 and / or the sensor device 34 are arranged completely below the mirror body 27, in particular in a cylindrical, in particular prism-shaped, in particular cuboid-shaped volume serving as a guide curve due to the reflection surface 26.

[0106] The suspension 31 and / or the actuator device 33 and / or the sensor device 34, in particular all of these elements, can be implemented as a microelectromechanical system (MEMS). They can, in particular, have a layered structure.

[0107] According to the invention, it was recognized that the requirements for the two-dimensional tilt angle range of the individual mirror 20 do not need to be isotropic. In particular, the maximum achievable tilt angle may be direction-dependent. This is illustrated by way of example in Figure 3. The x-axis represents the tilt angle range around the first tilt axis 35. The y-axis indicates the tilt angle range of the individual mirror 20 around the second tilt axis 36.

[0108] Fig. 3 shows an example of a requirement 37 for the two-dimensional tilt angle range of the individual mirror 20.

[0109] In the example shown in Figure 3, the two-dimensional tilt angle range of the individual mirror 20 is elliptical. This is not to be understood as limiting.

[0110] As an alternative to an elliptical design, the tilt angle range can also be rectangular.

[0111] The two tilting axes 35, 36 can, in particular, be parallel to the two semi-axes of the ellipse or parallel to the sides of the rectangle. The suspension 31 can, in particular, comprise a flexure joint. The suspension 31 can, for example, comprise one or more torsion beams or torsion springs or leaf springs 38. An exemplary embodiment of the leaf springs is shown in Fig. 8. The leaf springs 38 form a two-dimensional tilting joint.

[0112] The dimensions and materials of the leaf springs 38 can be adapted to the specified requirements for the tilt angle range of the individual mirror 20 for each of the tilt axes 35, 36. A corresponding adaptation is also possible for the design of the components of the actuator device 33 for each of the tilt directions.

[0113] The adaptation can be designed such that the combination of the restoring torque of the suspension 31 and the drive torque of the actuator device 33 enables the maximum required tilt angle to be achieved, wherein in particular a thermal and / or electrical resistance of the suspension 31 is reduced as much as possible at the same time.

[0114] In the case of torsion springs (not shown), this can be achieved by making the spring elements assigned to the axle with the lower tilt angle requirement shorter and / or thicker and / or wider than the spring elements assigned to the axle with the larger tilt angle requirement.

[0115] In the case of leaf springs 38, this can be achieved by making the spring elements assigned to the axis with the lower tilt angle requirement shorter and / or thicker and / or wider than the spring elements assigned to the axis with the greater tilt angle requirement. This is illustrated by way of example in Fig. 9. In this variant, the spring elements assigned to the second tilt axis 36 have a shorter spring length L2 than the spring elements assigned to the first tilt axis 35, which have a spring length LI.

[0116] The mechanical and / or thermal and / or electrical properties of the spring elements can also be influenced by a coating.

[0117] Another way to influence the stiffness of the suspension 31, particularly the leaf springs 38, is through the material selection. Spring elements assigned to the axle with the lower tilt angle requirement can be made of a material with a higher shear modulus and / or a higher elastic modulus. At the same time, they can have a higher thermal conductivity and / or a higher electrical conductivity than the spring elements assigned to the axle with the higher tilt angle requirement.

[0118] If the tilt angle requirements for a given axis are asymmetric, particularly if they differ in the positive and negative directions, the previously described adjustment of the spring elements can be combined with a pre-tilt of the mirror body 27 by a fixed tilt angle. The pre-tilt can be achieved, for example, by tilting the support 32.

[0119] The pre-tilt can be adjustable.

[0120] In the case of leaf springs 38, it may be provided to adjust the length, width, and / or thickness of the springs—that is, generally, their shape—so that the springs or a combination of springs are particularly stable in terms of their transverse stiffness, that is, their mechanical rigidity with respect to undesired movements. This allows parasitic tilting to be kept as small as possible. Parasitic tilting is tilting about an axis that is not parallel to the applied torque and / or perpendicular to the applied force.

[0121] Parasitic tilting and translational movements can preferably be kept as small as possible. This is particularly advantageous in an actuator device 33 with comb electrodes, in particular with parallel-oriented comb fingers or with radially oriented comb electrodes. This prevents an undesirably close approach of the movable electrodes 39 and the stator electrodes 40. This, in turn, prevents the actuator torque from being excessively dependent on the tilt angle for a given actuator voltage, i.e., from varying significantly with the inward and outward movement of the combs. As a result, the control of the positioning of the individual mirror 20 can be improved, especially at larger tilt angles.

[0122] Figure 4 schematically shows an exemplary embodiment of the actuator device 33. In this variant, the actuator device 33 comprises a plurality of electrodes 39, 40. The electrodes 39, 40 are designed in the form of comb fingers. They are particularly radially oriented. They are particularly arranged in a circular region.

[0123] The sensor device 34 can be designed accordingly. The electrodes 39 are connected to the mirror body 27. Thus, when the individual mirror 20 is displaced, they move together with the mirror body 27. They are therefore also referred to as movable electrodes 39.

[0124] The electrodes 40 are connected to the carrier 32. They form, in particular, stator electrodes.

[0125] The individual mirror 20, which can be tilted about the first tilt axis 35 and the second tilt axis 36, can in particular have four actuator elements, in particular in the form of electrode groups. The actuator elements can be used to generate the necessary actuator torques for tilting the individual mirror 20 about the two tilt axes 35, 36.

[0126] The adaptation of the individual actuator elements to the direction-dependent tilt angle range can be achieved, for example, by distributing, in particular unevenly distributing, the installation space for the individual actuator elements.

[0127] In the case of a piezoelectric bending actuator, the individual actuator elements can be realized on bending beams of different lengths and / or widths.

[0128] In the case of a capacitive comb actuator, electrodes of different lengths and / or a different number of comb electrode fingers can be assigned to the individual actuator elements.

[0129] In the case of a radial comb electrode tilt actuator, as shown by way of example in Fig. 4, adaptation of the actuator elements to the direction-dependent tilt angle range can be achieved by varying the distances between adjacent movable electrodes 39 and / or adjacent stator electrodes 40.

[0130] The distances between adjacent movable electrodes 39 and / or adjacent stator electrodes 40 can vary in particular depending on their azimuthal orientation.

[0131] According to the invention, it was recognized that the movable electrodes 39 are increasingly oriented non-parallel to the stator electrodes 40, the more their radial alignment deviates from the perpendicular to the tilt axis. This oblique immersion leads to a strong increase in the actuator torque at large tilt angles and thus a decreasing distance between a movable electrode 39 and the adjacent stator electrodes 40. To improve the controllability of the system, the distance between adjacent electrodes 39, 40 can be selected to be greater the larger the maximum tilt angle about an axis with the corresponding azimuthal orientation. In other words, the larger the maximum tilt angle, the greater the distance can be between adjacent electrodes 39, 40 that have the same azimuthal orientation as the respective tilt axis.

[0132] In the case of an elliptical tilting range (see Fig. 3), it can be provided, in particular, that comb fingers oriented perpendicular to the tilting axis with the larger tilting angle range are arranged at a smaller mutual distance than comb fingers oriented perpendicular to the tilting axis with the smaller tilting angle range. In the case of an elliptical tilting angle range, the distance between adjacent electrodes 39, 40 can, in particular, be continuously varied, in particular according to the tilting angle range. This is illustrated by way of example in Fig. 7. In this exemplary variant, the electrodes 39, which cause the mirror body 27 to tilt about the second tilting axis 36, have a greater distance than the electrodes 39, which cause the mirror body 27 to tilt about the first tilting axis 35. The same applies to the stator electrodes 40.

[0133] As schematically highlighted in Fig. 5, the configuration and / or arrangement of the electrodes 39 can be characterized by their spacing G and / or their length R in the radial direction. Both variables can be varied independently or in combination.

[0134] In the variant shown in Fig. 6, the electrodes 39i, which lead to the tilting of the mirror body 27 about the first tilt axis 35, have a smaller distance Gi than the electrodes 392, which lead to the tilting of the playing body 27 about the second tilt axis 36. The latter have a distance G2.

[0135] The variation of the distance G between the electrodes 39 and the variation of their length R can be independent of each other. The variations of the distance G and the length R can also be combined.

[0136] Increasing the distance G between adjacent electrodes 39 by a factor of F1 can lead to a reduction of the actuator torque with respect to the associated axis by a corresponding factor of F1. Reducing the electrode length R by a factor of F2 can lead to a reduction of the actuator torque about the corresponding axis by a corresponding factor of F2.

[0137] In the variant shown as an example in Fig. 6, the length R of all electrodes 39 was reduced by a factor of F2. At the same time, the distance G between the electrodes 39i was reduced by a factor of Fi, equal to F2. With this combination, the actuator torque for the first tilt axis 35 remains the same, while the actuator torque for the second axis 36 is reduced by a factor of F2.

[0138] By reducing the electrode length R, the installation space for the actuator device 33 could be reduced at the same time.

[0139] The arrangements of the electrodes 39 on the mirror body 27 shown as examples in Figs. 5 to 7 are also possible for the design and / or arrangement of the electrodes 40 on the carrier 32.

[0140] Preferably, the arrangement of the electrodes 40 on the carrier 32 is adapted to the design and arrangement of the electrodes 39 on the mirror body 27.

[0141] An increase in the rotational stiffness of the suspension 31 about a specific axis by a factor S can be achieved in the case of the spring elements being designed as leaf springs by a) increasing the width b of the springs by a corresponding factor S, b) increasing the thickness d of the springs by a factor [S c) reducing the length 1 of the springs by a factor S, or a suitable combination of these sizes.

[0142] An increase in the width b and / or a reduction in the length 1 of the leaf springs 38 leads to a reduction in the thermal and electrical resistance thereof.

[0143] Increasing the spring width B results in increased installation space. Reducing the spring length 1 is therefore usually more advantageous, at least as long as critical values ​​for the mechanical stresses within the spring are not reached.

Claims

Patent claims:

1. Individual mirror (20) for a facet mirror (13; 14) of an illumination optics (4) of a projection exposure system (1) comprising 1.1 a mirror body (27), 1.

2. a suspension (31) for pivotably supporting the mirror body (27) with two degrees of freedom of tilting and 1.

3. an actuator device (33) for pivoting the mirror body (27), 1.

4. wherein the suspension (31) and / or the actuator device (33) are designed such that the mirror body (27) has a direction-dependent tilt angle range, 1.5 wherein the actuator device (33) has a plurality of radially arranged actuator elements (39; 40), wherein the actuator elements (39; 40) have azimuthally varying distances.

2. Individual mirror (20) according to claim 1, characterized in that the suspension (31) is designed such that a rigidity of the suspension (31) with respect to a pivoting of the mirror body (27) about a first pivot axis (35) is greater than a rigidity of the suspension (31) with respect to a pivoting of the mirror body (27) about a second pivot axis (36).

3. Individual mirror (20) according to one of the preceding claims, characterized in that the suspension (31) has springs (38) of different stiffness.

4. Single mirror (20) according to one of the preceding claims, characterized in that the suspension (31) comprises springs (38) made of different materials.

5. Individual mirror (20) according to one of the preceding claims, characterized in that the suspension (31) has springs (38) with different coatings.

6. Individual mirror (20) according to one of the preceding claims, characterized in that the actuator device (33) is designed such that the maximum torque acting on the mirror body (27) that can be generated by means of the actuator device (33) is greater with respect to a first pivot axis (35) than with respect to a second pivot axis (36).

7. Individual mirror (20) according to one of the preceding claims, characterized in that the actuator device (33) has actuator elements which are arranged such that they have an uneven distribution.

8. Individual mirror (20) according to one of the preceding claims, characterized in that the actuator device (33) has differently designed actuator elements (39; 40) for different pivoting directions.

9. Individual mirror (20) according to one of the preceding claims, characterized in that the actuator device (33) has a different number of actuator elements (39; 40) for different pivoting directions.

10. Single mirror (20) according to one of the preceding claims, characterized in that the actuator device (33) and the suspension (31) are adapted to one another.

11. Single mirror (20) according to one of the preceding claims, characterized in that it is designed as a MEMS (micro-electromechanical system) or MOEMS (micro-opto-electromechanical system).

12. Facet mirror (13; 14) for an illumination optics (4) of a projection exposure system (1) comprising 12.1 a plurality of individual mirrors (20), 12.

2. wherein at least one non-empty subset of the individual mirrors (20) is designed according to one of the preceding claims.

13. Facet mirror (13; 14) according to claim 12, characterized in that at least two of the individual mirrors (20) have different pre-tilts.

14. Illumination optics (4) for a projection exposure system (1) comprising at least one facet mirror (13; 14) according to one of claims 12 to 13.

15. Lighting system (2) for a projection exposure system (1) comprising 15.

1. an illumination optics (4) according to claim 14 and 15.

2. a radiation source (3) for generating illumination radiation (10).

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