Optical assembly and manufacturing method thereof, method for deforming an optical element, and projection exposure apparatus

Abstract

The present invention relates to an optical assembly (1) comprising an optical element having an optically active front side (3) and a back side (4) opposite the front side (3). The optical assembly (1) comprises a number of electrostatic actuators (5) distributed along the back side (4) of the optical element (2). Each actuator (5) is actuated by an electrical control voltage (U) between the electrodes (6, 7) of an electrode pair. 1...n The optical element (2) is configured and mechanically coupled to a back side (4) of the optical element (2) such that an electrostatic force generated by the electrode (6) and serving to deform the optical element (2) is transmitted to the optical element (2). A dielectric (8) is disposed between the electrodes (6, 7) of the electrode pair.

Description

[Technical field]

[0001] This application claims priority to German Patent Application No. 10 2021 202 769.5, filed March 22, 2021, which is incorporated herein by reference in its entirety and forms part of the present disclosure.

[0002] The present invention relates to an optical assembly that includes an optical element having an optically active front side and a back side opposite the front side, and a plurality of electrostatic actuators distributed along the back side of the optical element.

[0003] The invention further relates to a method for deforming an optical element by means of a plurality of electrostatic actuators and to a computer program product having program code means for carrying out said method.

[0004] The present invention also relates to a method of manufacturing an optical assembly that includes an optical element having an optically active front side and a back side opposite the front side, and a plurality of electrostatic actuators.

[0005] The invention furthermore relates to a microlithographic projection exposure apparatus comprising an illumination system having a radiation source, an illumination optical unit, and a projection optical unit. [Background technology]

[0006] Projection exposure apparatus or lithography apparatus are used in the production of high-precision integrated circuits, whereby optical elements such as mirrors and / or lens elements direct the light of a radiation source onto a wafer to be exposed, the arrangement, position and shape of the optical elements contributing decisively to the quality of the exposure in this case.

[0007] The ever-increasing miniaturization of semiconductor circuits places increasingly stringent demands on both the resolution and the accuracy of projection exposure apparatus, which in turn places correspondingly stringent demands on their optical elements and their operation in particular.

[0008] In order to increase the imaging accuracy of a projection exposure apparatus, experience has shown that optical elements can be deformed in a targeted manner by means of actuable components in order to correct imaging aberrations in the projection exposure apparatus. For this purpose, ferroelectric actuators are usually attached to the optical elements, which facilitate actuation based on the piezoelectric or electrostrictive principle. By driving the individual actuators, it is finally possible to set a target profile of the optical elements, for example of mirrors, and thus to correct the optical system.

[0009] To be able to operate with sufficient accuracy, known actuation systems often require closed-loop operation and therefore constant detection of the deformations actually performed. However, the use of sensors with a sufficiently high measurement accuracy is not always possible, especially in lithographic apparatus. For this reason, known actuation systems often have a feedforward operation. For this purpose, sufficient accuracy requires comprehensive system modeling, which requires a deep system understanding of the influence of the individual actuators on the optical elements. All disturbances and non-idealities that are not taken into account directly affect the performance that can be obtained by the actuation system.

[0010] In this case, temperature changes may represent one of the most important disturbance variables. As an example, the temperature of optical elements in a projection exposure apparatus may vary in the range of 20 °C to 40 °C. Further problems in system modeling relate to the inherent non-repeatability of the actuators, e.g. creep, hysteresis, thermal hysteresis, variations in behavior and / or variations in thermal expansion coefficients.

[0011] Therefore, in addition to temperature calibration, electrostriction and thermal hysteresis and actuator drift need to be modeled and calibrated to facilitate high-precision positioning or deformation of optical elements, which is only possible with very high measurement costs and very comprehensive measurement equipment.

[0012] The problems of the actuator's material-specific non-repeatability (e.g. hysteresis and creep) and strong temperature dependence can be avoided by switching to electrostatic-based actuators, whose dynamic effect is based on the force of an electric field acting between two adjacent electrodes. As an example, the use of electrostatic actuators to deform mirrors has been proposed in the general patent application US 2003 / 0139993.

[0013] However, a problem with the deformation of optical elements by electrostatic actuators is that the dynamic effect is relatively limited compared to conventional actuators, for example compared to ferroelectric actuators. To enhance the dynamic effect, US Pat. No. 6,233,933 proposes the use of complex nanolaminate films, for example.

[0014] US Pat. No. 5,399,433 also considers the use of electrostatic actuators to deform the mirror. To enhance the dynamic effect, the use of interdigitated electrodes with interlocking comb teeth is proposed.

[0015] However, the methods proposed in EP 1 239 633 and EP 1 236 933 for increasing the dynamic effect of the electrostatic actuator for the deformation of the mirror are relatively complicated. Moreover, it was surprisingly found that even in the case of the measures proposed in the above-mentioned documents, the force of the electrostatic actuator itself is generally insufficient, and in particular is not sufficient to deform optical elements of the projection exposure apparatus. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent No. 7,692,838 [Patent Document 2] DE 10 2016 209 847 A1 Summary of the Invention [Problem to be solved by the invention]

[0017] In view of the known prior art, it is an object of the present invention to provide an optical assembly that facilitates deformation of optical elements with high precision and high dynamic efficiency.

[0018] The invention is also based on the object of providing a method for deforming an optical element, which facilitates the deformation of the optical element with high precision and high dynamic efficiency.Finally, it is also an object of the invention to provide an advantageous computer program product for carrying out said method.

[0019] It is a further object of the present invention to provide a method for producing an optical assembly, which allows for producing an improved optical assembly for deforming an optical element.

[0020] Finally, it is also an object of the invention to provide a microlithography projection exposure apparatus comprising at least one optical assembly having an optical element which is deformable with high precision by at least one electrostatic actuator in order to correct image aberrations. [Means for solving the problem]

[0021] This object is achieved by the respective independent claims for an optical assembly, a deformation method, a computer program product, a method for manufacturing an optical assembly and a projection exposure apparatus. The dependent claims and the features described below relate to advantageous embodiments and variants of the invention.

[0022] An optical assembly is provided that includes an optical element having an optically active front side and a back side opposite the front side.

[0023] The back side of the optical element may also possibly have an optically active form, for example if the optical element is in the form of a lens element, however the back side is preferably not optically active, or at least is not used to influence the beam path from the radiation source.

[0024] The optically active front side of the optical element is preferably in the form of a mirror surface that reflects or influences the beam path, in particular of DUV ("deep ultraviolet") or EUV ("extreme ultraviolet") radiation.

[0025] The rear side of the optical element may extend in a parallel or at least substantially parallel plane to the front side, in particular in the undeformed basic state of the optical element. However, this is not required within the scope of the invention. The front side and / or the rear side may also have an arcuate form, in particular may be concave or convex.

[0026] According to the invention, an optical assembly includes a plurality of electrostatic actuators distributed along a rear side of an optical element, each of the electrostatic actuators having an electrode pair of two spaced apart electrodes.

[0027] The electrodes preferably have a flat morphology, but may also have an arched, stepped and / or comb-like structure. Planar electrodes are preferably provided, for example in the form of a slab, a film or a deposited layer. By way of example, the thickness of the individual electrodes may be 0.01 μm to 500 μm, preferably 0.01 μm to 100 μm, very preferably 0.01 μm to 10 μm.

[0028] The two electrodes of a common electrode pair may each be integrally formed, but may also have a multi-part embodiment. Thus, insofar as "electrode" is mentioned within the scope of this specification, this refers in principle to a single electrode or a group of several individual electrodes that together form an electrode. Thus, a single actuator is not excluded from having three or more individual electrodes. Furthermore, an individual actuator may also include several electrode pairs, each consisting of two spaced apart electrodes. This is not necessarily important within the scope of the present invention, and for the sake of simplicity, the present invention is described below on the basis of an actuator that essentially includes exactly one electrode pair or exactly two spaced apart electrodes. However, this should not be understood as limiting.

[0029] In accordance with the invention, each actuator is configured and mechanically coupled to the back side of the optical element such that an electrostatic force, generated by an electrical control voltage between the electrodes of an electrode pair, is transmitted to the optical element, which force serves to deform the optical element.

[0030] If necessary, the optical assembly can have exactly one actuator for the target deformation of the optical element. However, it is preferred that the optical assembly has a plurality of actuators, particularly preferably the optical assembly comprises at least 2 actuators, at least 10 actuators, at least 50 actuators, at least 100 actuators, at least 500 actuators, at least 1,000 actuators, at least 5,000 actuators or at least 10,000 actuators for the target deformation of the optical element. However, it is particularly preferred that the optical assembly has a much larger number of actuators.

[0031] The actuators are preferably equidistant from each directly adjacent actuator or evenly distributed across the back side of the optical element.

[0032] As a result of the actuator, the optical element may be elastically or at least substantially reversibly deformable. The deformation of the optical element is preferably performed without hysteresis.

[0033] "Deformation" is to be understood in particular to mean a deformation of the material of the optical element, which may result for example in a length change per part of the material of the optical element or a surface deformation per part of the optical element.

[0034] As a result of using electrostatic actuators, positioning accuracy problems caused by inherent actuator non-repeatability can be reduced or avoided entirely, since the dynamic effects are determined solely by the electric field forces between the electrodes of an electrode pair.

[0035] Since electrostatic drives or actuators produce the greatest dynamic effect at small plate separations, it is preferable to minimize the distance provided between the electrodes of an electrode pair. However, the maximum electrostatic force may be limited by the breakdown voltage at which statically induced ionization leads to an avalanche of ionized electrons between the two electrodes. It is known that the breakdown voltage can be described by Paschen's law and can be dependent on each actuator.

[0036] According to the invention, a dielectric is disposed between the electrodes of the electrode pair.

[0037] Preferably a solid or liquid dielectric is provided, although a gas dielectric may also be provided (but preferably not air or hydrogen).

[0038] In one development of the invention, in particular the dielectric can have a dielectric strength greater than the dielectric strength of air.

[0039] As a result of using a dielectric (particularly a solid or liquid dielectric), it is possible to increase the dielectric strength of the actuator and, in the case of a correspondingly high dielectric constant, it is even possible to increase the force of the actuator. By way of example, to the knowledge of the inventors, the maximum force between the electrodes of an electrode pair using air as the dielectric is 100 mm 2 , and thus only about 0.004 N. As a result of the use according to the invention of a dielectric, preferably not air, between the electrodes of an electrode pair, this force can be increased enough to actually facilitate deformation of the optical element.

[0040] The dielectric may completely fill the space between the electrodes of the electrode pair. However, the dielectric may also only partially fill the space between the electrodes of the electrode pair, for example being centrally located between the electrodes of the electrode pair and spaced apart from one or both electrodes. In order to increase the dielectric strength of the actuator, one or both electrodes of the electrode pair may be covered, for example coated, with a dielectric, in particular in the manner of an insulating layer.

[0041] Preferably, a dielectric is provided which has a dielectric constant greater than 1.0 (or greater than a vacuum), preferably greater than air, in particular greater than 2, particularly preferably greater than 5, very particularly preferably greater than 10, even more preferably greater than 50, for example also greater than 100.

[0042] Particularly when a solid dielectric is provided, the dielectric is preferably compressible to facilitate changes in the distance between the electrodes of an electrode pair during operation of the actuator.

[0043] In an advantageous development of the invention, one of the electrodes of the electrode pair can be designed as a control electrode to which a control voltage can be applied, the other electrode being preferably designed as a reference electrode to which a reference potential can be applied.

[0044] The reference electrode is preferably embodied as a ground electrode, and the reference potential is preferably the ground potential.

[0045] In particular, a reference potential may be applicable to a reference electrode of the actuator and to a reference electrode of at least one, preferably all, of the further actuators.

[0046] Contacting the actuators can be greatly simplified by combining the reference electrodes or by a common contact for all reference electrodes.

[0047] According to one development of the invention, one electrode of the electrode pair can be mechanically coupled to a rear side of the optical element, and the other electrode can be mechanically coupled to a reference body spaced apart from the rear side of the optical element.

[0048] Preferably, the control electrodes are mechanically coupled to the reference body and the reference electrodes are mechanically coupled to the rear side of the optical element, which allows easy accessibility of the control electrodes for actuation or application of a control voltage.

[0049] In particular, the fiducials may be part of the optical body, a mount for the optical element, a mounting frame for the optical element (e.g. a mounting frame of an optical unit or a test bench), or a housing part for the optical element. Typically, the fiducials are statically coupled to the surrounding components.

[0050] Preferably, the electrode is materially connected to the optical element, in particular to the rear side of the optical element. In principle, the electrode can be connected to the optical element in any desired manner, for example by press-fit or form-fit. However, it has been found that a material connection, for example by gluing the electrode to the optical element or by vapor deposition of the electrode to the optical element, is particularly suitable. An embodiment of the electrode and the optical element in one piece can also be provided, for example by using additive manufacturing techniques. The same attachment techniques can be used for attaching the other electrode to the reference body.

[0051] According to one development of the invention, the electrodes associated with the optical element can be attached directly to the optical element.

[0052] This allows deformations to be introduced into the optical element in a particularly targeted manner, however it does not allow the introduction of global modes into the optical element, although this may be envisaged for various applications.

[0053] For this purpose, in an alternative development of the invention, the electrodes coupled to the optical element can be indirectly connected to the optical element via an intermediate element spaced apart from the rear side of the optical element.

[0054] The electrodes can be attached to the intermediate element and / or the intermediate element can be connected to the optical element by the attachment techniques already described within the scope of attachment of the electrodes to the optical element.

[0055] The intermediate element can thus act as a balance plate, thus allowing the introduction of global modes into the optical element or the implementation of "longer wavelength" deformations of the optical element. Thus, the deformations of the actuators can first affect the intermediate element directly and then be transferred to the optical element via the intermediate element.

[0056] Depending on the application, the skilled artisan may or may not provide an intermediate element and may vary the thickness and elastic or material properties of the intermediate element as required.

[0057] In one development of the invention, the intermediate element can be attached to the optical element by means of spacer elements and / or spacer struts distributed along the rear side of the optical element.

[0058] The spacer elements / spacer struts can be attached to the optical element and / or intermediate element by the attachment techniques already described within the scope of the attachment of the electrodes to the optical element.

[0059] The influence of the actuator on the optical element via the intermediate element can be optimally set by the use of spacer elements and / or spacer struts, for example by varying the geometric shape of the spacer elements or spacer struts and / or the material properties of the spacer elements or spacer struts.

[0060] By way of example, the individual spacer elements and / or spacer struts may be positioned midway or centrally (with respect to the electrode surface) with respect to the electrodes of each actuator.

[0061] In an advantageous development of the invention, the reference body can be attached to the optical element or the intermediate element via bearing units and / or bearing struts distributed along the rear side of the optical element.

[0062] The bearing units / bearing struts can be attached to the optical element and / or to the intermediate element and / or to the reference body by the attachment techniques already described within the scope of the attachment of the electrodes to the optical element.

[0063] Preferably, the electrodes of each actuator are arranged between the individual bearing units and / or bearing struts, in this way favourable force distribution can be promoted.

[0064] In one development of the invention, the spacer units or spacer struts can be offset from the bearing units or bearing struts along the rear side of the optical element.

[0065] In this way, the optical element can be deformed over a wide range without being limited by its support on a reference body.

[0066] In an advantageous development of the invention, the electrodes coupled to the optical element can extend parallel to the rear side of the optical element.

[0067] In principle, however, it is also possible to provide an arrangement of the electrodes on the rear side of the optical element that deviates from the parallel range, however the parallel range has proven to be particularly suitable and can also be implemented relatively easily from a technical point of view.

[0068] In an advantageous development of the invention, an electrode (preferably a control electrode) coupled to the optical element can be arranged on a side wall of a recess extending into the optical element from the rear side.

[0069] In some cases, furthermore, the electrode coupled to the reference body (preferably the reference electrode) may be arranged on a protrusion extending from the reference body into the recess of the optical element. In some cases, the electrode coupled to the reference body may form the protrusion itself.

[0070] Preferably, the electrodes of an electrode pair are arranged orthogonally or at least substantially orthogonally to the rear and / or front side of the optical element when in the base state they extend into or through the recess.

[0071] In particular, the recesses may be small width slots, for example slots with a width of a few micrometers.

[0072] As described, application of a control voltage can generate forces in the recesses and thus deformations in the optical element, which can further lead to deformations of the optically active front side of the optical element. In this way, it is also possible to induce a global deformation in the optical element.

[0073] In an advantageous development of the invention, both electrodes of an electrode pair can be mechanically coupled to the optical element and for this purpose arranged on opposite side walls of a recess extending into the optical element from the rear side.

[0074] In particular, the two electrodes can be evaporated or glued onto two opposing side walls.

[0075] In one development of the invention, the dielectric may be a liquid medium.

[0076] The liquid medium may preferably be distilled water or formamide, but in principle any desired dielectric medium may be provided, in particular one with high dielectric strength and high dielectric constant.

[0077] The use of a liquid medium as the dielectric has proven to be particularly suitable.

[0078] It should be noted that when combining different dielectrics, especially different liquid media, the total breakdown voltage may be determined by which dielectric layer first reaches its respective critical potential difference or electric field strength.

[0079] Where a gas dielectric is provided this may be, for example, sulphur hexafluoride (SF6).

[0080] High vacuum may also be advantageously suitable.

[0081] According to this development of the invention, fluid connections can be provided between electrode pairs of adjacent actuators in order to facilitate the exchange of liquid medium between the actuators.

[0082] In the case of an incompressible liquid medium, it can be ensured that it flows out of the gap between the electrodes upon actuation to facilitate movement of the actuator.

[0083] In particular, the fluid connections between the actuators may be recesses, bores or the like in the bearing units and / or bearing struts, preferably extending between the individual actuators.

[0084] According to this development, the optical assembly may have at least one balance reservoir fluidly connected to one of the actuators, to multiple actuators, or to all of the actuators, to facilitate the expansion and entry of the liquid medium.

[0085] In particular, the balance vessel may be a balance bellows that is elastically expandable and contractable depending on the amount of fluid medium contained therein.

[0086] The balance reservoir can in particular ensure that the optical element does not deform as a result of thermal expansion of the dielectric. The balance reservoir, in particular the balance bellows, can accommodate excess liquid in case of thermal expansion of the liquid medium or in case of reduction of the gap between the electrodes of the common electrode pair due to actuation.

[0087] To prevent crosstalk between the actuators, it may be advantageous to provide a separate balancing reservoir for each actuator or for individual groups of actuators.

[0088] According to one development, the optical assembly may further comprise at least one inlet and at least one outlet for the liquid medium, which may be fluidly connected to the actuator so that the liquid medium can rinse the electrode pairs of the actuator.

[0089] Additionally, turbomachinery, such as a pump, may optionally be provided to facilitate the passage of the liquid medium.

[0090] In particular, the inlet may be connected to an external liquid source, in which case the balancing vessel may possibly be omitted.

[0091] In an advantageous development of the invention, the electrodes of an electrode pair can be arranged extending parallel to one another.

[0092] However, in some cases, the electrodes of an electrode pair may be arranged at an angle to each other, however this is not preferred.

[0093] In an advantageous development of the invention, the actuators can be distributed in a grid along the rear side of the optical element.

[0094] As a result of a grid-like distribution of actuators it may be possible to set different deformation profiles.Preferably the actuators are distributed among the bearing units and / or bearing struts.

[0095] By way of example, the actuators may be arranged in rectangular segments. Furthermore, there is the option of arranging them in individual longitudinal slots in only one spatial direction. An arrangement in the form of a triangle or any other grid-like arrangement may also be provided.

[0096] According to one development of the invention, the optical assembly may comprise a control device which generates a control voltage for the actuator in order to cause a targeted deformation of the optical element.

[0097] The control device may be in the form of a microprocessor, or alternatively any further device implementing the control device, such as one or more arrangements of discrete electrical components on a printed circuit board, a programmable logic controller (PLC), an application specific integrated circuit (ASIC), or any other programmable circuit, such as a field programmable gate array (FPGA), a programmable logic array (PLA), and / or a commercially available computer.

[0098] According to one development of the invention, the control device can be configured to use the actuator as a sensor unit by excitation with a control voltage in a frequency range that is not critical for the deformation operation in order to record the actual state of deformation.

[0099] Therefore, in some cases, the actuator can also be used as a sensor unit by estimating the current state of deformation from the electrical behavior of the two electrodes of a common electrode pair. The actuation with the control voltage for the operation as a sensor unit can be performed in the high frequency range, for example, on the order of several megahertz. Since the actuation during use as an actuator is generally performed with a bandwidth on the order of several hundred hertz, in this case the operation of the actuator and the sensor can be performed in parallel, generally without mutual interference.

[0100] The invention also relates to a method for deforming an optical element by means of a plurality of electrostatic actuators, each having an electrode pair of two spaced apart electrodes. A control voltage is applied between the electrodes of the electrode pair to generate an electrostatic force, which is transferred from the actuator to the optical element for the purpose of deforming the optical element. Furthermore, a dielectric is arranged between the electrodes of the electrode pair. Preferably, a solid or liquid dielectric is provided. However, a gaseous dielectric or a high vacuum may also be provided.

[0101] The use of electrostatic actuators can be particularly advantageous since the force or extension is not generated by the properties of the material itself, as is common with piezoelectric or electrostrictive actuators, but is based on the attraction of electric charges, and therefore the forces generated during actuation are much easier to predict and model.

[0102] The use of electrostatic actuators to deform optical elements according to the present invention can provide a high precision system, since electrostatic actuators have very low non-repeatable properties and their dynamic effect can be significantly increased by the use of a dielectric between the electrodes of an electrode pair according to the present invention.

[0103] By applying control voltages or reference potentials to the electrodes, tensile or compressive forces can be generated arbitrarily between the electrodes involved. It is preferred to generate a tensile force.

[0104] The invention further relates to a computer program product comprising program code means for carrying out the method for deforming an optical element as described above and below when the program is executed on a control device, in particular on a control device of said optical assembly.

[0105] In particular, the invention is suitable for use in a projection exposure apparatus as described further below or in lithographic optical systems in general, but in principle the invention may also be suitable for any desired application in which optical elements are to be deformed, in particular aerospace and astronomy applications, and also military applications.

[0106] The invention also relates to a method for manufacturing an optical assembly comprising an optical element having an optically active front side and a back side opposite the front side, and a plurality of electrostatic actuators, each having an electrode pair of two spaced apart electrodes. The actuators are mechanically coupled to the back side of the optical element such that an electrostatic force is transmitted to the optical element, which is generated by an electrical control voltage between the electrodes of the electrode pair and serves to deform the optical element. Furthermore, a dielectric is introduced between the electrodes of the electrode pair. Preferably, a solid or liquid dielectric is provided. However, a gaseous dielectric or a high vacuum may also be provided.

[0107] The techniques described in US Pat. No. 6,399,633 for establishing mechanical connections between optical elements, reference bodies, intermediate elements, spacer elements / spacer struts, bearing units / bearing struts, and / or electrodes can be used to advantage within the scope of the present invention, the disclosure of which is incorporated herein in its entirety by this reference.

[0108] In particular, the individual elements of the optical component may be connected to each other by silicate bonding or direct bonding, or by adhesive connections, solder connections, etc., in particular with regard to the connections between the support units / support struts and the optical elements and / or reference bodies.

[0109] The application of electrodes to the optical element, the reference body and / or the intermediate element can be carried out, for example, by deposition of a conductive layer. Other techniques for applying electrodes can also be performed. In principle, any material, form-fit and / or press-fit connection technique may be possible.

[0110] The invention also relates to a microlithographic projection exposure apparatus comprising an illumination system having a radiation source, an illumination optical unit, and a projection optical unit, the illumination optical unit and / or the projection optical unit comprising at least one optical assembly as defined above and below.

[0111] The invention is particularly suitable for correcting imaging aberrations in projection exposure apparatus by deformation of optical elements of an optical assembly.

[0112] The invention is particularly suitable for use in microlithographic DUV projection exposure apparatus, but especially in EUV projection exposure apparatus. A possible application of the invention also relates to immersion lithography.

[0113] Advantageously, the features described in relation to one of the subject matters of the invention, in particular the optical assembly, the method for modifying an optical element, the computer program product, the method for manufacturing an optical assembly and the projection exposure apparatus, can also be implemented in relation to the other subject matters of the invention. Similarly, advantages stated in relation to one of the subject matters of the invention can also be understood in relation to the other subject matters of the invention.

[0114] It should further be noted that terms such as "comprising", "having" or "including" do not exclude other features or steps. Furthermore, words such as "a(n)" or "the" indicating individual steps or features do not exclude a plurality of features or steps and vice versa.

[0115] However, in a purist embodiment of the invention, the features introduced in the invention using the terms "comprises", "has" or "includes" may be considered as exhaustive recitations. Thus, one or more recitations of features may be considered as complete within the scope of the invention, for example, when considered separately for each claim. For example, the invention may consist only of the features recited in claim 1.

[0116] The designations "first" or "second" etc. are used primarily to distinguish between features of each apparatus or method and are not necessarily intended to indicate that features are mutually necessary or interrelated.

[0117] It should further be emphasized that the values ​​and parameters described herein also include deviations or variations of not more than ±10%, preferably not more than ±5%, more preferably not more than ±1%, and especially very preferably not more than ±0.1 from the respective specified value or parameter, provided that these deviations are not excluded in the practice of the invention. The specification of ranges by starting and ending values ​​also includes all values ​​and fractions included in the respective specified ranges, in particular the starting and ending values ​​as well as the respective average values.

[0118] The invention also relates to an optical assembly according to claim 1, comprising an optical element and at least one electrostatic actuator having at least two spaced apart electrodes, the actuator being configured and mechanically coupled to the optical element such that an electrostatic force generated between the electrodes of the actuator is transferred to the optical element for deforming, aligning and / or positioning the optical element. Further features of claim 1 and the dependent claims and features described herein relate to advantageous embodiments and variants of this optical assembly.

[0119] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings.

[0120] Each of the figures shows preferred exemplary embodiments showing individual features of the present invention in combination with one another. The features of the exemplary embodiments may also be implemented separately from other features of the same exemplary embodiment and therefore may be easily combined by those skilled in the art to form further advantageous combinations and subcombinations with the features of other exemplary embodiments.

[0121] In the drawings, functionally identical elements are labeled with the same reference numbers. [Brief description of the drawings]

[0122] [Figure 1] 1 shows a schematic meridian section of an EUV projection exposure apparatus; [Diagram 2] 1 shows a schematic representation of a DUV projection exposure apparatus; [Diagram 3]1A and 1B are schematic cross-sectional side views of an optical assembly including a plurality of electrostatic actuators having an optical element, a reference body, and a solid dielectric disposed between the reference body and the optical element; [Figure 4] 4A and 4B are schematic diagrams of a portion of a cross-sectional view taken along section line IV of FIG. 3, illustrating a grid-like arrangement of actuators along the back side of the optical element; [Diagram 5] 13A and 13B show schematic cross-sectional side views of an optical assembly according to yet another exemplary embodiment having inlets and outlets for a liquid dielectric and a fluid connection between an actuator. [Figure 6] 13A and 13B show schematic cross-sectional side views of an optical assembly according to yet another exemplary embodiment having a balance reservoir for a liquid dielectric and a fluid connection between the actuators; [Figure 7] 13A and 13B show schematic cross-sectional side views of an optical assembly according to yet another exemplary embodiment having multiple balancing reservoirs for liquid dielectrics and fluid connections between actuators; [Figure 8] Schematically shows a cross-sectional side view of an optical assembly according to yet another exemplary embodiment having a balance container for a liquid dielectric, a fluid connection between the actuators, and an intermediate element arranged between the actuators and the optical element. [Figure 9] 13A and 13B are schematic diagrams illustrating a cross-sectional side view of an optical assembly according to yet another exemplary embodiment having an electrode disposed in a recess on the back side of the optical element, in a non-deflected state of the actuator; [Figure 10] The optical assembly of FIG. 9 is shown diagrammatically in a deflected state of the actuator. [Figure 11] 10A and 10B show schematic diagrams of examples of actuator grid arrangements for the optical assembly shown in FIG. [Figure 12] 10A and 10B show schematic examples of yet another grating arrangement of actuators of the optical element shown in FIG. [Figure 13] 13A and 13B are schematic cross-sectional side views of optical assemblies according to yet another exemplary embodiment having electrodes disposed within recesses on the back side of the optical elements; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0123] 1, the essential components of a microlithography EUV projection exposure apparatus 100 are exemplarily described below. The description of the basic structure of the EUV projection exposure apparatus 100 and its components should not be construed as limiting here.

[0124] In addition to the radiation source 102, the illumination system 101 of the EUV projection exposure apparatus 100 comprises an illumination optical unit 103 for illumination of an object field 104 in an object plane 105. Here, a reticle 106 arranged in the object field 104 is exposed. The reticle 106 is held by a reticle holder 107. The reticle holder 107 is displaceable, in particular in the scanning direction, by a reticle displacement drive 108.

[0125] To aid in illustration, a Cartesian xyz coordinate system is shown in Figure 1. The x direction extends perpendicular to the plane of the figure. The y direction extends horizontally and the z direction extends vertically. In Figure 1, the scan direction extends in the y direction. The z direction extends perpendicular to the object plane 105.

[0126] The EUV projection exposure apparatus 100 comprises a projection optical unit 109. The projection optical unit 109 serves to image the object field 104 into an image field 110 in an image plane 111. The image plane 111 extends parallel to the object plane 105. Alternatively, angles other than 0° between the object plane 105 and the image plane 111 are also possible.

[0127] Structures on the reticle 106 are imaged onto a photosensitive layer of a wafer 112, which is arranged in the region of an image field 110 of an image plane 111. The wafer 112 is held by a wafer holder 113. The wafer holder 113 is displaceable, in particular in the y-direction, by a wafer displacement drive 114. The displacement of the reticle 106 by the reticle displacement drive 108 on the one hand and the displacement of the wafer 112 by the wafer displacement drive 114 on the other hand can be performed synchronously with respect to one another.

[0128] The radiation source 102 is an EUV radiation source. The radiation source 102 in particular emits EUV radiation 115, also referred to below as working radiation or illumination radiation. In particular, the working radiation 115 has a wavelength in the range of 5 nm to 30 nm. The radiation source 102 may be a plasma source, for example an LPP source ("laser produced plasma") or a GDPP source ("gas discharge plasma"). It may also be a synchrotron-based radiation source. The radiation source 102 may be a free electron laser (FEL).

[0129] The illumination radiation 115 coming from the radiation source 102 is focused by the collector 116. The collector 116 may be a collector with one or more ellipsoidal and / or hyperbolic reflecting surfaces. On at least one reflecting surface of the collector 116 the illumination radiation 115 may be incident at grazing incidence (GI), i.e. at an angle of incidence greater than 45°, or at normal incidence (NI), i.e. at an angle of incidence smaller than 45°. The collector 116 may be structured and / or coated, firstly to optimize its reflectivity for the used radiation 115 and secondly to suppress extraneous light.

[0130] Downstream of the collector 116, the illumination radiation 115 propagates through an intermediate focus in an intermediate focal plane 117. The intermediate focal plane 117 may represent a separation between the source module comprising the radiation source 102 and the collector 116 and the illumination optics unit 103.

[0131] The illumination optical unit 103 comprises a deflection mirror 118 and a first facet mirror 119 arranged downstream thereof in the beam path. The deflection mirror 118 may be a plane deflection mirror or a mirror with a beam-influencing effect beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 118 may be in the form of a spectral filter that separates the used optical wavelength of the illumination radiation 115 from extraneous light of wavelengths deviating therefrom. If the first facet mirror 119 is arranged in a plane of the illumination optical unit 103 that is optically conjugate with the object plane 105 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 119 comprises a plurality of individual first facets 120, also referred to as field facets in the following. Only some of these first facets 120 are exemplarily shown in FIG. 1 .

[0132] The first facet 120 may be in the form of a macroscopic facet, in particular a rectangular facet, or a facet having an arcuate or partial circular peripheral contour. The first facet 120 may be in the form of a planar facet, or a convexly or concavely curved facet.

[0133] The first facet 120 itself can also consist of a number of individual mirrors, in particular a number of micromirrors, as is known, for example, from DE 10 2008 009 600. The first facet mirror 119 can in particular be formed as a microelectromechanical system (MEMS system). See DE 10 2008 009 600 for further details.

[0134] Illumination radiation 115 travels horizontally, ie along the y-direction, between collector 116 and deflection mirror 118 .

[0135] In the beam path of the illumination optical unit 103, a second facet mirror 121 is arranged downstream of the first facet mirror 119. If the second facet mirror 121 is arranged in a pupil plane of the illumination optical unit 103, it is also referred to as a pupil facet mirror. The second facet mirror 121 can also be arranged away from the pupil plane of the illumination optical unit 103. In this case, the combination of the first facet mirror 119 and the second facet mirror 121 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747, EP 1 614 008 and US 6,573,978.

[0136] The second facet mirror 121 includes a plurality of second facets 122. In the case of a pupil facet mirror, the second facets 122 are also referred to as pupil facets.

[0137] The second facet 122 may likewise be a macroscopic facet, which may have, for example, a circular, rectangular or hexagonal perimeter, or may be a facet made up of a micromirror. In this respect, reference is also made to DE 10 2008 009 600 A1.

[0138] The second facet 122 may have a planar reflective surface or a convexly or concavely curved reflective surface.

[0139] The illumination optical unit 103 results in a doublet. This basic principle is also called a fly's eye integrator.

[0140] It may be advantageous not to position the second facet mirror 121 exactly in a plane that is optically conjugate with the pupil plane of the projection optical unit 109 .

[0141] The individual first facets 120 are imaged into the object field 104 by means of a second facet mirror 121. The second facet mirror 121 is the last beam-shaping mirror in the beam path upstream of the object field 104 or indeed the final mirror for the illumination radiation 115.

[0142] In yet another embodiment (not shown) of the illumination optical unit 103, a transfer optical unit, which notably contributes to the imaging of the first facet 120 into the object field 104, may be arranged in the beam path between the second facet mirror 121 and the object field 104. The transfer optical unit may have exactly one mirror or two or more mirrors arranged one behind the other in the beam path of the illumination optical unit 103. In particular, the transfer optical unit may include 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).

[0143] In the embodiment shown in FIG. 1, the illumination optical unit 103 comprises exactly three mirrors downstream of the collector 116 , in particular a deflection mirror 118 , a field facet mirror 119 and a pupil facet mirror 121 .

[0144] In yet another embodiment of the illumination optical unit 103, the deflection mirror 118 can also be omitted, so that the illumination optical unit 103 then has exactly two mirrors downstream of the collector 116, specifically a first facet mirror 119 and a second facet mirror 121.

[0145] Typically, the imaging of the first facet 120 onto the object plane 105 by the second facet 122 or using the second facet 122 and the transfer optical unit is only an approximate imaging.

[0146] The projection optical unit 109 comprises a number of mirrors Mi, which are numbered according to their location in the beam path of the EUV projection exposure apparatus 100 .

[0147] In the example shown in Fig. 1, the projection optical unit 109 comprises six mirrors M1 to M6. A substitution of 4, 8, 10, 12 or any other number of mirrors Mi is equally possible. The penultimate mirror M5 and the final mirror M6 each have an aperture for the illumination radiation 115 to pass through. The projection optical unit 109 is a double-shielded optical unit. The projection optical unit 109 has an image-side numerical aperture which is greater than 0.5, may be greater than 0.6, and may be, for example, 0.7 or 0.75.

[0148] The reflective surface of the mirror Mi may be embodied as a freeform surface without an axis of rotational symmetry. Alternatively, the reflective surface of the mirror Mi may be designed as an aspheric surface with exactly one axis of rotational symmetry of the reflective surface shape. As with the mirrors of the illumination optical unit 103, the mirror Mi may have a coating that is highly reflective with respect to the illumination radiation 115. These coatings may be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0149] The projection optical unit 109 has a large object-image offset in the y direction between the y coordinate of the center of the object field 104 and the y coordinate of the center of the image field 110. In the y direction, this object-image offset may be approximately the same size as the z distance between the object plane 105 and the image plane 111.

[0150] In particular, the projection optical unit 109 can have an anamorphic form. In particular, it has different imaging scales βx, βy in the x-direction and the y-direction. The two imaging scales βx, βy of the projection optical unit 109 are preferably (βx, βy)=(+ / -0.25, + / -0.125). A positive imaging scale β means imaging without image inversion. A negative sign of the imaging scale β means imaging with image inversion.

[0151] The projection optical unit 109 results in a size reduction in the x-direction, ie perpendicular to the scanning direction, with a ratio of 4:1.

[0152] The projection optical unit 109 provides a size reduction of 8:1 in the y-direction, ie the scanning direction.

[0153] Other imaging scales are possible as well. Imaging scales of the same sign and the same absolute value in the x and y directions, for example 0.125 or 0.25, are also possible.

[0154] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 104 and the image field 110 may be the same or may differ depending on the embodiment of the projection optical unit 109. Examples of projection optical units with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303.

[0155] Each of the pupil facets 122 is assigned to exactly one of the field facets 120 in order to form a respective illumination channel that illuminates the object field 104. In particular, this makes it possible to obtain an illumination according to the Köhler principle. The far field is decomposed into a number of object fields 104 by means of the field facets 120. The field facets 120 generate a number of images of intermediate foci on the respectively assigned pupil facets 122.

[0156] By means of the respectively assigned pupil facets 122, the field facets 120 are imaged onto the reticle 106 in an overlapping manner in order to illuminate the object field 104. The illumination of the object field 104 is in particular as uniform as possible. Its uniformity error is preferably less than 2%. By overlapping the different illumination channels, field uniformity can be obtained.

[0157] The illumination of the entrance pupil of the projection optical unit 109 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels, and in particular the subset of pupil facets, which guide the light, the intensity distribution in the entrance pupil of the projection optical unit 109 can be set. This intensity distribution is also called the illumination setting.

[0158] An equally favorable pupil uniformity in the region of a defined illuminated portion of the illumination pupil of the illumination optical unit 103 can be achieved by redistribution of the illumination channels.

[0159] Further aspects and details of the illumination of the object field 104, in particular the entrance pupil of the projection optical unit 109, are described below.

[0160] In particular, the projection optical unit 109 may have a concentric entrance pupil. It may be accessible. It may be inaccessible.

[0161] The entrance pupil of the projection optical unit 109 cannot always be illuminated exactly by the pupil facet mirror 121. In the case of imaging of the projection optical unit 109 telecentrically imaging the center of the pupil facet mirror 121 onto the wafer 112, the aperture rays often do not intersect at a single point. However, it is possible to find a surface for which the determined distance of the pair of aperture rays is minimal. This surface represents the entrance pupil or a real space surface conjugate thereto. In particular, this surface has a finite curvature.

[0162] The projection optical unit 109 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transfer optical unit, should be provided between the second facet mirror 121 and the reticle 106. This optical component can be used to take into account the difference in the relative positions of the tangential and sagittal entrance pupils.

[0163] In the arrangement of the components of the illumination optical unit 103 shown in Fig. 1, the pupil facet mirror 121 is arranged in a plane conjugate with the entrance pupil of the projection optical unit 109. The field facet mirror 119 is arranged at an incline with respect to the object plane 105. The first facet mirror 119 is arranged at an incline with respect to the arrangement plane defined by the deflection mirror 118.

[0164] The first facet mirror 119 is disposed so as to be inclined with respect to the arrangement plane defined by the second facet mirror 121 .

[0165] 2 shows an exemplary DUV projection exposure apparatus 200. The DUV projection exposure apparatus 200 comprises an illumination system 201, an apparatus known as a reticle stage 202 which accommodates and precisely positions a reticle 203 which determines the subsequent structures on a wafer 204, a wafer holder 205 which holds, moves and precisely positions the wafer 204, and an imaging apparatus, in particular a projection optical unit 206, which has a number of optical elements, in particular lens elements 207, which are held by mounts 208 in a lens housing 209 of the projection optical unit 206.

[0166] Alternatively or in addition to the illustrated lens elements 207, various refractive, diffractive and / or reflective optical elements, particularly mirrors, prisms, end plates, etc. may also be provided.

[0167] The basic functional principle of a DUV projection exposure tool 200 is that a structure introduced on a reticle 203 is imaged onto a wafer 204 .

[0168] The illumination system 201 provides a projection beam 210 in the form of electromagnetic radiation required for imaging the reticle 203 onto the wafer 204. A laser, a plasma source, etc. can be used as the source of this radiation. The radiation is shaped in the illumination system 201 by optical elements such that the projection beam 210 has the desired properties in terms of diameter, polarization, shape of the wavefront, etc. upon incidence on the reticle 203.

[0169] An image of the reticle 203 is produced by the projection beam 210 and transferred in a suitably reduced form from the projection optical unit 206 onto the wafer 204. In this case, the reticle 203 and the wafer 204 can be moved synchronously so that each area of ​​the reticle 203 is imaged onto a corresponding area of ​​the wafer 204 virtually in succession during a so-called scanning process.

[0170] The air gap between the final lens element 207 and the wafer 204 can be optionally replaced with a liquid medium having a refractive index greater than 1.0. The liquid medium can be, for example, high purity water. Such an arrangement is also called immersion lithography and has high photolithographic resolution.

[0171] The use of the invention is not limited to use in the projection exposure apparatus 100, 200, nor to projection exposure apparatuses having the specifically described configuration. The invention and the following exemplary embodiments should not be understood as being limited to a particular design. The following figures show the invention very diagrammatically, purely as an example.

[0172] Targeted deformations of projection exposure apparatus, for example of optical elements 118, 119, 120, 121, 122, Mi, 207 of the projection exposure apparatus 100, 200, can be particularly suitable for the correction of imaging aberrations of said apparatus. This is the starting point of the present invention.

[0173] 3 to 13 exemplarily and very diagrammatically show various exemplary embodiments of an optical assembly 1 according to the invention. The optical assembly 1 facilitates a targeted deformation of an optical element 2, in particular for correcting imaging aberrations in a projection exposure apparatus 100, 200. The optical element 2 to be deformed can in particular be arranged in the illumination optical unit 103 and / or the projection optical unit 109, 206 of the projection exposure apparatus 100, 200.

[0174] In the exemplary embodiment, the optical element 2 is exemplarily illustrated as a mirror, which should not be construed as limiting. The optical element 2 has an optically active front side 3 and a rear side 4 opposite the front side. Upon entering the optical element 2, the illumination radiation 115 or the projection beam 210 is influenced in a defined way by the optically active front side 3, in particular to steer the beam path.

[0175] First, a first exemplary embodiment of an optical assembly 1 according to the present invention will be described with reference to FIGS.

[0176] The optical assembly 1 comprises a plurality of electrostatic actuators 5 distributed along the back side 4 of the optical element 2. In particular, the actuators 5 may be distributed in a grid pattern along the back side 4 of the optical element 2, as can be particularly well seen on the basis of Fig. 4. Each of the actuators 5 has an electrode pair of two spaced apart electrodes 6, 7.

[0177] Preferably, the electrodes 6, 7 of a common electrode pair are arranged extending parallel to one another (in the undeflected state), as shown in all exemplary embodiments, however, in principle an inclined arrangement with respect to one another can also be provided.

[0178] Each actuator 5 is connected to an electrical control voltage U between the electrodes 6, 7 of an electrode pair. 1...n The actuators 5 are configured and mechanically coupled to a back side 4 of the optical element 2 such that an electrostatic force generated by the actuators 5 and serving to deform the optical element 2 is transmitted to the optical element 2. Figure 3 and the subsequent Figures 5-7 each show one of the actuators 5 in a deflected state, and therefore the optical element 2 in a partially deformed state.

[0179] In order to obtain a sufficiently high dynamic effect and to increase the dielectric strength between the electrodes 6, 7, a solid or liquid dielectric 8 is arranged between the electrodes 6, 7 of the electrode pair. Optionally, a gas dielectric 8 may be provided, but preferably a gas dielectric 8 that is not air. In the exemplary embodiment of Fig. 3, a solid medium is provided as the dielectric 8, which is hidden in Fig. 4 for the purposes of illustration. In contrast, in the subsequent exemplary embodiments, a liquid medium is provided.

[0180] Preferably, the solid medium according to the exemplary embodiment of Figures 3 and 4 is deformable to facilitate a shortening of the distance between the electrodes 6, 7 in the deflected state of the actuator 5. However, alternatively, the dielectric 8 may not completely fill the gap between the electrodes 6, 7. By way of example, the dielectric 8 may be located only on one of the two electrodes 6, 7 or the electrodes 6, 7 may be coated with an insulating layer of the dielectric 8. In this way, the dielectric strength and force of the actuator 5 may be increased.

[0181] In an exemplary embodiment, one of the electrodes of the electrode pair is coupled to a control voltage U 1...n The other electrode is in the form of a reference electrode 7 and can be applied, together with further reference electrodes 7 of other actuators 5, to a common reference potential GND.

[0182] 3-8 and 13, one of the electrodes 6, 7, preferably the reference electrode 7 as shown, is mechanically coupled to the back side 4 of the optical element 2. The other electrode 6, 7, preferably the control electrode 6 as shown, is mechanically coupled to a reference body 9 that is spaced from the back side 4 of the optical element 2.

[0183] By way of example, the reference body 9 may be a mount for the optical element 2, a mounting frame for the optical element 2, or even the optical element 2 itself.

[0184] In the exemplary embodiment of Figures 3 to 7, the datum 9 is attached to the optical element 2 by means of longitudinal struts 10 (see also in particular Figure 4) distributed along the back side 4 of the optical element 2. The individual actuators 5 are arranged between the individual support struts 10. In the exemplary embodiment of Figures 3 to 8, the actuators 5 are aligned parallel to the back side 4 of the optical element 2.

[0185] A control device 11, shown by a dashed line in FIG. 3, controls the control voltage U 1...n The control device 11 may be arranged to cause a targeted deformation of the optical element 2.

[0186] However, the control device 11 operates in a frequency range that is not important for the deformation operation, i.e., the control voltage U 1...nThe control device 11 may be configured to use the actuator 5 as a sensor unit, by excitation at . In this way it is possible to capture the actual state of deformation of the optical element 2, for example in higher frequency bands. The methods for deforming the optical element 2 described above and below can be implemented as a computer program product having program code means on the control device 11.

[0187] The dielectric 8 is preferably a liquid medium, in particular distilled water or formamide. A corresponding embodiment is shown for example in FIG. 5. In order to facilitate the exchange of the liquid medium between the actuators 5, in the exemplary embodiment of FIGS. 5 to 13, a respective fluid connection is established between the electrode pairs of adjacent actuators 5. In the exemplary embodiment of FIGS. 5 to 8, the fluid connection between the actuators 5 is realized by a respective bore 12 through the bearing strut 10 arranged between the actuators 5. An inlet 13 and an outlet 14 for the liquid medium can be provided, which are fluidly connected to the actuators 5, as shown in FIG. 5, so that the electrode pairs of the actuators 5 are rinsed by the liquid medium. For this purpose, further possibly a turbomachine, for example a pump (not shown), can be provided.

[0188] However, in a particularly preferred embodiment, as shown in the following exemplary embodiment, a closed system is provided. In this case, it is preferred that the liquid medium can be expandable, in particular to facilitate thermal expansion and / or deformation of the dielectric 8 when the actuator 5 is deflected. In this respect, a balance container 15 can for example be provided, which is fluidly connected to one of the actuators 5 and thus facilitates the liquid medium to expand into it (via the fluid connection network). A balance bellows is exemplarily illustrated. It is also possible to provide several balance containers 15, for example one balance container 15 per actuator 5 as shown in FIG. 7, in order to facilitate the separation of the actuators 5 from each other.

[0189] In the exemplary embodiment shown in Figures 3 to 7, one electrode 6, 7 of the electrode pair, in this case the respective reference electrode 7, is attached directly to the optical element 2. This makes it possible to facilitate a local or short wavelength deformation of the optical element 2 as shown. However, insofar as a global deformation or a longer wavelength deformation is desired, the electrodes 6, 7 (especially the reference electrode 7) coupled to the optical element 2 can be indirectly connected to the optical element 2 via an intermediate element 16 spaced apart from the rear side 4 of the optical element 2. This is illustrated on the basis of Figure 8.

[0190] In this case, the reference body 9 can be attached to the intermediate element 16 via bearing struts 10, which are themselves attached to the optical element 2 via spacer struts 17 distributed along the back side 4 of the optical element 2. The bearing struts 10 and the spacer struts 17 can be arranged offset along the back side 4 of the optical element 2, the spacer struts 17 being arranged on the optical element 2 as centrally as possible below the actuator or electrode surface. In this way, the optical element 2 can be influenced particularly advantageously.

[0191] 8, the intermediate element 16 can provide an amount of separation of the individual actuators 5 from the optical element 2, thereby allowing for global or long wavelength deformation of the optical element 2, which can be advantageous in some applications.

[0192] Alternative embodiments of the optical assembly 1 are shown in Figures 9 to 12. Figure 9 shows the optical assembly 1 in a non-deflected state of the actuator 5, and Figure 10 shows said optical assembly in a deflected state of the actuator 5, which should be understood as being purely exemplary and merely schematic.

[0193] Figures 11 and 12 show possible grid arrangements for the distribution of actuators 5 along the back side 4 of the optical element 2. The variants shown in Figures 9 to 12 are particularly suitable for a rectangular distribution arrangement (see Figure 11) or a linear arrangement (see Figure 12).

[0194] The dielectric 8 is hidden in Figures 9 to 13 for simplicity of illustration. Again, a liquid medium is preferably provided. In the exemplary embodiment of Figures 9 to 13, the fluid connection between the actuators 5 is provided by suitable spacing of the reference bodies 9 and the resulting formed channels 18. Purely by way of example, a common balance reservoir 15 is provided.

[0195] As can be seen on the basis of figures 9 and 10, both electrodes 6, 7 of the electrode pair may be mechanically coupled to the optical element 2. For this purpose, the electrodes 6, 7 may in particular be arranged on opposite side walls of a recess 19, for example a slot, from the back side 4 of the optical element 2. The side walls may for example be coated (fully or partially) with a conductive medium. A suitable electrical control voltage U 1...n When applied to the electrode pair, tensile and / or compressive forces can be introduced directly into the optical element 2, causing deformation at the optically active front side 3 of the optical element 2. Similar to the exemplary embodiment of FIG. 8 with the intermediate element 16, relatively long wavelength or global deformations may also be achievable in this manner.

[0196] Fig. 13 shows yet another exemplary embodiment of the optical assembly 1. In this case too, the electrode 7 is bonded to the optical element 2 and for this purpose is arranged on the side wall of a recess 19 extending from the back side 4 into the optical element 2. In contrast, the electrode 6 bonded to the reference body 9 is arranged on (or forms itself in) a protrusion 20 extending from the reference body 9 into the recess 19 of the optical element 2. Advantageously, again, forces can be introduced directly into the optical element 2, similar to what was explained on the basis of the exemplary embodiment of Figs. 9 and 10. In addition to the channels between the actuators 5, bores 12 can be provided in the protrusions 20 to provide a fluid connection.

[0197] Optionally, in the exemplary embodiment of FIG. 13, instead of one electrode pair, two electrode pairs are provided as shown, with the control electrodes 6 electrically connected to each other and applied with the same control voltage U 1...n, each aligned against one of the side walls of the recess 19. In this way the effective electrode area can be doubled.

[0198] Of course, it is also possible to provide a structure in which the reference electrode 7 protrudes from the reference body 9 into the recess 19 .

[0199] It should be noted that in principle the illustrated exemplary embodiments can always be combined with one another, if not excluded from a technical point of view. Furthermore, further embodiments of the alignment / arrangement of the actuator 5 and the electrodes 6, 7 of the electrode pair can be provided. In particular, the illustrated geometrical relations and scales are purely schematic and exemplary and should not be interpreted as being to scale.

[0200] Further options for increasing the electrostatic force could be interdigitation of the electrodes 6, 7 in a common electrode pair and / or splitting of the individual electrodes 6, 7 into multiple individual electrodes.

Claims

1. An optical assembly (1) comprising an optical element (2) having an optically active front side (3) and a back side (4) opposite to the front side (3), and a number of electrostatic actuators (5) distributed along the back side (4) of the optical element (2), each actuator (5) comprising an electrode pair of two spaced apart electrodes (6, 7), each actuator (5) being actuated by an electrical control voltage (U) between the electrodes (6, 7) of the electrode pair. １...ｎ 1. An optical assembly (1) configured and mechanically coupled to the back side (4) of the optical element (2) such that an electrostatic force generated by an electrostatic force generating element (21) and serving to deform the optical element (2) is transmitted to the optical element (2), the electrostatic force being generated by an electrostatic force generating element (21) and serving to deform the optical element (2), the optical assembly being characterized in that a dielectric (8) is disposed between the electrodes (6, 7) of the electrode pair, one electrode (6, 7) of the electrode pair being mechanically coupled to the back side (4) of the optical element (2) and the other electrode (7, 6) being mechanically coupled to a reference body (9) spaced from the back side (4) of the optical element (2), the electrodes (6, 7) coupled to the optical element (2) being disposed on a side wall of a recess (19) extending from the back side (4) into the optical element (2), and the electrodes (7, 6) coupled to the reference body (9) being disposed on a protrusion (20) extending from the reference body (9) into the recess (19) of the optical element (2).

2. An optical assembly (1) comprising an optical element (2) having an optically active front side (3) and a back side (4) opposite to the front side (3), and a number of electrostatic actuators (5) distributed along the back side (4) of the optical element (2), each actuator (5) comprising an electrode pair of two spaced apart electrodes (6, 7), each actuator (5) being actuated by an electrical control voltage (U) between the electrodes (6, 7) of the electrode pair. １...ｎ 1. An optical assembly (1) configured and mechanically coupled to the back side (4) of the optical element (2) such that an electrostatic force generated by an electrostatic force generating means (4) and serving to deform the optical element (2) is transmitted to the optical element (2), characterized in that a dielectric (8) is arranged between the electrodes (6, 7) of the electrode pair, both electrodes (6, 7) of the electrode pair being mechanically coupled to the optical element (2) and arranged on opposite side walls of a recess (19) extending into the optical element (2) from the back side (4) for this purpose.

3. An optical assembly (1) as described in claim 1 or 2, characterized in that the dielectric (8) is a solid or liquid dielectric (8).

4. An optical assembly (1) according to any one of claims 1 to 3, characterized in that the dielectric (8) has a dielectric constant greater than the dielectric constant in a vacuum, preferably greater than the dielectric constant of air.

5. An optical assembly (1) according to any one of the preceding claims, characterized in that the dielectric (8) has a dielectric strength greater than the dielectric strength of air.

6. In an optical assembly (1) according to any one of the preceding claims, one electrode of the electrode pair is designed as a control electrode (6), and the control voltage (U １...ｎ ), and the other electrode is designed as a reference electrode (7) and can be applied with a common reference potential (GND) together with a reference electrode (7) of at least one further actuator (5).

7. 2. An optical assembly (1) according to claim 1, characterized in that the electrodes (6, 7) associated with the optical element (2) are directly attached to the optical element (2).

8. 2. The optical assembly (1) of claim 1, characterized in that the electrodes (6, 7) coupled to the optical element (2) are indirectly connected to the optical element (2) via an intermediate element (16) spaced from the back side (4) of the optical element (2).

9. 9. The optical assembly (1) according to claim 8, characterized in that the intermediate element (16) is attached to the optical element (2) by means of spacer elements and / or spacer struts (17) distributed along the back side (4) of the optical element (2).

10. An optical assembly (1) according to any one of claims 1, 7 to 9, characterized in that the reference body (9) is attached to the optical element (2) or on an intermediate element (16) via bearing units and / or bearing struts (10) distributed along the back side (4) of the optical element (2).

11. 10. The optical assembly (1) according to claim 9, characterized in that the spacer elements or spacer struts (17) are offset from the support units or support struts (10) along the back side (4) of the optical element (2).

12. An optical assembly (1) according to any one of claims 1, 7 to 11, characterized in that the electrodes (6, 7) bonded to the optical element (2) extend parallel to the back side (4) of the optical element (2).

13. Optical assembly (1) according to any one of the preceding claims, characterized in that the dielectric (8) is a liquid medium, preferably distilled water or formamide.

14. 14. The optical assembly (1) according to claim 13, characterized in that a fluid connection is formed between the electrode pairs of adjacent actuators (5) to facilitate the exchange of the liquid medium between the actuators (5).

15. 15. An optical assembly (1) according to claim 13 or 14, characterized by at least one balance reservoir (15) fluidly connected to one of the actuators (5), to a plurality of the actuators (5), or to all of the actuators (5) to facilitate the expansion and entry of the liquid medium.

16. An optical assembly (1) according to any one of claims 13 to 15, characterized by at least one inlet (13) and at least one outlet (14) for the liquid medium fluidly connected to the actuator (5) so that the liquid medium can rinse the electrode pair of the actuator (5).

17. An optical assembly (1) according to any one of the preceding claims, characterized in that the electrodes (6, 7) of the electrode pair are arranged extending parallel to each other.

18. 18. An optical assembly (1) according to any one of the preceding claims, characterized in that the actuators (5) are distributed in a grid along the back side (4) of the optical element (2).

19. An optical assembly (1) as described in any one of claims 1 to 18, characterized by a control device (11) generating a control voltage (U 1...n ) for the actuator (5) for the purpose of deforming the optical element (2) in a desired manner.

20. In the optical assembly (1) according to claim 19, the control device (11) is adapted to measure the control voltage (U) in a frequency range which is not important for the deformation operation in order to record the actual state of the deformation. １．．．ｎ ) using the actuator as a sensor unit.

21. A method for deforming an optical element (2) by means of a plurality of electrostatic actuators (5), each having an electrode pair of two spaced apart electrodes (6, 7), comprising applying a control voltage (U) between the electrodes (6, 7) of the electrode pairs in order to generate an electrostatic force that is transferred from the actuators (5) to the optical element (2) in order to deform the optical element (2), １．．．ｎ 2. A method for applying a voltage to an optical element, comprising the steps of: applying a voltage to an optical element; applying a voltage to the ...

22. A method for deforming an optical element (2) by means of a plurality of electrostatic actuators (5), each having an electrode pair of two spaced apart electrodes (6, 7), comprising applying a control voltage (U) between the electrodes (6, 7) of the electrode pairs in order to generate an electrostatic force that is transferred from the actuators (5) to the optical element (2) in order to deform the optical element (2), １．．．ｎ ) is applied, characterized in that a dielectric (8) is arranged between the electrodes (6, 7) of the electrode pair, both electrodes (6, 7) of the electrode pair being mechanically coupled to the optical element (2) and arranged on opposite side walls of a recess (19) extending into the optical element (2) from its back side (4).

23. A computer program product comprising program code means for carrying out the method for deforming an optical element (2) according to claim 21 or 22 when executed on a control device (11).

24. A method for manufacturing an optical assembly (1) comprising an optical element (2) having an optically active front side (3) and a back side (4) opposite to the front side (3), and a number of electrostatic actuators (5) each having an electrode pair of two spaced apart electrodes (6, 7), the actuators (5) being actuated by an electrical control voltage (U １...ｎ 1. A method for mechanically coupling an electrostatic force generated by a dielectric material (6, 7) to the back side (4) of an optical element (2) according to the invention, the electrostatic force being capable of being transmitted to the optical element (2), the electrostatic force being generated by a dielectric material (6, 7) and serving to deform the optical element (2), characterized in that a dielectric (8) is introduced between the electrodes (6, 7) of the electrode pair, one electrode (6, 7) of the electrode pair being mechanically coupled to the back side (4) of the optical element (2) and the other electrode (7, 6) being mechanically coupled to a reference body (9) spaced apart from the back side (4) of the optical element (2), the electrodes (6, 7) coupled to the optical element (2) being arranged on a side wall of a recess (19) extending from the back side (4) into the optical element (2), and the electrodes (7, 6) coupled to the reference body (9) being arranged on a protrusion (20) extending from the reference body (9) into the recess (19) of the optical element (2).

25. A method for manufacturing an optical assembly (1) comprising an optical element (2) having an optically active front side (3) and a back side (4) opposite to the front side (3), and a number of electrostatic actuators (5) each having an electrode pair of two spaced apart electrodes (6, 7), the actuators (5) being actuated by an electrical control voltage (U １...ｎ ), capable of transmitting to said optical element (2) electrostatic forces generated by said electrode pair (6, 7) and serving to deform said optical element (2), characterized in that a dielectric (8) is introduced between said electrodes (6, 7) of said electrode pair, both electrodes (6, 7) of said electrode pair being mechanically coupled to said optical element (2) and arranged on opposite side walls of a recess (19) which extends for this purpose from said back side (4) into said optical element (2).

26. A microlithography projection exposure apparatus (100, 200) with an illumination system (101, 201) comprising a radiation source (102), an illumination optical unit (103), and a projection optical unit (109, 206), wherein the illumination optical unit (103) and / or the projection optical unit (109, 206) comprises at least one optical assembly according to any one of the preceding claims.

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