DE102021202769A1 - Optical assembly and method for its manufacture, method for deforming an optical element and projection exposure system - Google Patents

Abstract

The invention relates to an optical assembly (1), having an optical element (2) with an optically active front side (3) and a rear side (4) facing away from the front side (3). The optical assembly (1) comprises a plurality of electrostatic actuators (5) distributed along the back (4) of the optical element (2). The actuators (5) each have an electrode pair of two spaced-apart electrodes (6, 7), the actuators (5) each being set up and mechanically coupled to the back (4) of the optical element (2) in such a way that a an electrical control voltage (U1...n) between the electrodes (6, 7) of the electrode pair generated electrostatic force for deformation of the optical element (2) is transmitted to the optical element (2). A dielectric (8) is arranged between the electrodes (6, 7) of the pair of electrodes.

Description

The invention relates to an optical assembly, having an optical element with an optically active front side and a rear side facing away from the front side, and a plurality of electrostatic actuators arranged distributed along the rear side of the optical element.

The invention also relates to a method for deforming an optical element using a plurality of electrostatic actuators and a computer program product with program code means for carrying out such a method.

The invention also relates to a method for producing an optical assembly, which has an optical element with an optically active front side and a rear side facing away from the front side, and a plurality of electrostatic actuators.

The invention also relates to a projection exposure system for microlithography with an illumination system that has a radiation source, illumination optics and projection optics.

Projection exposure systems or lithography systems are used to produce integrated circuits with high precision. Here, the light from a radiation source is directed to a wafer to be exposed via optical elements such as mirrors and/or lenses. The arrangement, position and shape of the optical elements make a decisive contribution to the quality of the exposure.

Due to the progressive miniaturization of semiconductor circuits, the requirements for the resolution and the accuracy of the projection exposure systems are increasing in equal measure. Correspondingly high demands are placed in particular on their optical elements and the actuation of the optical elements.

In order to increase the imaging accuracy of a projection exposure system, it is known from practice to deform optical elements in a targeted manner using components that can be actuated, in order to correct imaging errors within the projection exposure system. For this purpose, ferroelectric actuators are usually attached to the optical elements, which enable actuation based on the piezoelectric or electrostrictive principle. Finally, by controlling each individual actuator, it is possible to set specific profiles of the optical element, for example a mirror, and thus to correct the optical system.

The known actuation systems often require regular operation and thus constant detection of the deformation that has actually taken place in order to be operated with sufficient accuracy. However, it is not always possible to use a sensor with a sufficiently high measurement accuracy, particularly within lithography systems. For this reason, the known actuation systems are often operated in an open control chain (“feed forward”). For this, a comprehensive system modeling is required for sufficient accuracy, which requires a deep system understanding of the influence of the individual actuator on the optical element. All disturbances or non-idealities that are not taken into account have a direct effect on the performance that can be achieved with the actuation system.

One of the biggest disruptive variables can be the change in temperature. For example, the temperature of an optical element can change in a range between 20° C. and 40° C. within a projection exposure system. Other problems in system modeling relate to intrinsic non-reproducibility of the actuators, such as creep, hysteresis, thermal hysteresis, variation in behavior and/or variations in thermal expansion coefficients.

In order to enable high-precision positioning or deformation of the optical element, modeling and calibration of the electrostrictive and thermal hysteresis as well as the actuator drift must be carried out in addition to the temperature calibration. This is only possible with a great deal of measuring effort and very extensive measuring equipment.

The problem of the non-reproducibility of the actuator intrinsic to the material (e.g. hysteresis and creep) and the strong temperature dependency can be circumvented by switching to electrostatically acting actuators. The force effect of electrostatic actuators is based on the force of an electric field that acts between two adjacent electrodes. The use of electrostatic actuators for the deformation of mirrors is, for example, in the generic U.S. 7,692,838 B2 suggested.

However, one problem with the deformation of optical elements by means of electrostatic actuators is the comparatively limited force effect compared to conventional actuators, for example compared to ferroelectric actuators. In order to increase the force effect, for example in the U.S. 7,692,838 B2 proposed to use complex nanolaminate films.

Also the DE 10 2016 209 847 A1 deals with the use of electrostatic actuators to deform mirrors. In order to increase the force effect, the use of comb-shaped electrodes with interlocking comb teeth is proposed.

The one in the U.S. 7,692,838 B2 and the DE 10 2016 209 847 A1 However, the proposed methods for increasing the force of electrostatic actuators for the deformation of mirrors are comparatively complex. Furthermore, it has surprisingly been found that the force of the electrostatic actuators, even in the case of the measures proposed in the publications mentioned, is generally not sufficient, in particular not for the deformation of optical elements in projection exposure systems.

In view of the known state of the art, the object of the present invention is to provide an optical assembly which enables an optical element to be deformed with high precision and high force.

The present invention is also based on the object of providing a method for deforming an optical element, which allows deformation of an optical element with high precision and high force. Finally, it is also the object of the invention to provide an advantageous computer program product for carrying out the method mentioned.

In addition, the object of the invention is to provide a method for producing an optical assembly, by means of which an improved optical assembly for deforming an optical element can be produced.

Finally, it is also an object of the invention to provide a projection exposure system for microlithography, which has at least one optical assembly with an optical element that can be deformed with high precision by at least one electrostatic actuator in order to correct imaging errors.

The object is achieved for the optical assembly, the method for deformation, the computer program product, the method for producing the optical assembly and the projection exposure system with the respective independent claims. The dependent claims and the features described below relate to advantageous embodiments and variants of the invention.

An optical assembly is provided, having an optical element with an optically active front side and a rear side facing away from the front side.

The rear side of the optical element can optionally also be designed to be optically active, for example if the optical element is designed as a lens. However, the rear side is preferably not optically active or is at least not used to influence the beam path of a radiation source.

The optically active front side of the optical element is preferably designed as a mirror surface, in particular for reflecting or influencing the beam path of DUV (“Deep Ultra Violet”) or EUV (“Extreme Ultra Violet”) radiation.

The back of the optical element can run plane-parallel or at least essentially plane-parallel to the front, in particular in the non-deformed basic state of the optical element. However, this is not absolutely necessary within the scope of the invention. The front and/or the back can also be arched, in particular concave or convex.

According to the invention, the optical assembly has a plurality of electrostatic actuators distributed along the rear side of the optical element. The electrostatic actuators each have a pair of electrodes made up of two electrodes spaced apart from one another.

The electrodes are preferably flat, but can also have a curved, stepped and/or comb-like structure. Flat electrodes are preferably provided, for example in the form of a plate, a foil or a vapor-deposited layer. The thickness of an individual electrode can be, for example, 0.01 μm to 500 μm, preferably 0.01 μm to 100 μm, particularly preferably 0.01 μm to 10 μm.

The two electrodes of a common pair of electrodes can each be formed in one piece, but optionally also in several pieces. Insofar as “one” electrode is spoken of in the context of the present description, it can in principle be an individual electrode or a combination of a plurality of individual electrodes which together form the electrode. Accordingly, it cannot be ruled out that an individual actuator has more than two individual electrodes. Furthermore, a single actuator can also have a plurality of electrode pairs, each consisting of two electrodes spaced apart from one another. This is not necessarily important in the context of the invention; for simplification, the invention is essentially described below using actuators that have exactly one pair of electrodes has exactly two spaced electrodes. However, this should not be understood as restrictive.

According to the invention, the actuators are each set up and mechanically coupled to the back of the optical element in such a way that an electrostatic force generated between the electrodes of the electrode pair by means of an electrical control voltage is transmitted to the optical element to deform the optical element.

If necessary, the optical assembly can have precisely one actuator for the targeted deformation of the optical element. However, the optical assembly preferably has a plurality of actuators, particularly preferably the optical assembly has at least two actuators, at least ten 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 targeted deformation of the optical element. However, the optical assembly particularly preferably has significantly more actuators.

The actuators are preferably spaced equidistant from the actuators immediately adjacent to them or are distributed uniformly over the rear side of the optical element.

The optical element can be elastically or at least essentially reversibly deformable by the actuators. The optical element is preferably deformed without hysteresis.

Under the "deformation" is to be understood in particular a deformation of the material of the optical element, whereby z. B. a sectional change in length in the material of the optical element or a sectional surface deformation of the optical element can be caused.

By using electrostatic actuators, the problems of positioning accuracy caused by intrinsic non-reproducibility of the actuator can be reduced or completely avoided, since the effect of the force is determined solely by the force of the electric field between the electrodes of the electrode pair.

The smallest possible distance between the electrodes of the electrode pair is preferably provided, since an electrostatic drive or the electrostatic actuator can develop the greatest force for small plate distances. However, the maximum possible electrostatic force can be limited by the breakdown voltage above which static ionization leads to an ionization avalanche between the two electrodes. As is known, the breakdown voltage can be described using Paschen's law and can be determined accordingly for the respective actuator.

According to the invention, a dielectric is arranged between the electrodes of the electrode pair.

A solid or liquid dielectric is preferably provided, but a gaseous dielectric can also be provided (but preferably not air or hydrogen).

In a development of the invention, it can be provided in particular that the dielectric has a dielectric strength greater than the dielectric strength of air.

The use of a dielectric (in particular a solid or liquid dielectric) can increase the dielectric strength of the actuator and, with a correspondingly high dielectric constant, also the force of the actuator. The inventors have recognized, for example, that the maximum force when using air as a dielectric between the electrodes of the electrode pair with an electrode area of 100 mm ² would only be 3 V/μm and thus only about 0.004 N. By the proposed use of a dielectric between the electrodes of the pair of electrodes, which is preferably not air, this force can be increased sufficiently to allow deformation of an optical element in practice.

It can be provided that the dielectric completely occupies the space between the electrodes of the electrode pair. However, it can also be provided that the dielectric only partially occupies the space between the electrodes of the electrode pair, for example being arranged centrally between the electrodes of the electrode pair and spaced apart from one or both electrodes. Provision can also be made for one or both electrodes of the electrode pair to be covered with the dielectric, for example to be coated, in particular in the form of an insulating layer, in order to increase the dielectric strength of the actuator.

A dielectric with a permittivity greater than 1.0 (or greater than a vacuum) is preferably provided, preferably with a permittivity greater than air, in particular with a permittivity greater than 2, particularly preferably with a permittivity greater than 5, very particularly preferably with a permittivity greater 10, more preferably with one Permittivity greater than 50, for example with a permittivity greater than 100 or more.

In particular when a solid dielectric is provided, the dielectric is preferably compressible in order to allow the distance between the electrodes of the electrode pair to vary during operation of the actuator.

In an advantageous development of the invention, it can be provided that one of the electrodes of the pair of electrodes is designed as a control electrode and can be supplied with the control voltage. The other electrode of the pair of electrodes is preferably designed as a reference electrode and can be subjected to a reference potential.

The reference electrodes are preferably designed as grounding or grounding electrodes. The reference potential is preferably a ground potential.

In particular, provision can be made for the reference potential to be applied to the reference electrode of the actuator together with a reference electrode of at least one of the further actuators, preferably all actuators.

The contacting of the actuators can be significantly simplified by combining the reference electrodes or by common contacting of all reference electrodes.

According to a development of the invention, it can be provided that one of the electrodes of the pair of electrodes is mechanically coupled to the rear side of the optical element and the other electrode is mechanically coupled to a reference body spaced apart from the rear side of the optical element.

The control electrode is preferably mechanically coupled to the reference body and the reference electrode is mechanically coupled to the rear side of the optical element. In this way, the accessibility of the control electrodes for driving or applying the control voltage can be facilitated.

The reference body can in particular be a part of the optical body, a mount for the optical element, a mounting frame for the optical element (for example a mounting frame for an optical system or a test stand) or a housing part for the optical element. The reference body is usually statically coupled to a surrounding component.

The electrode is preferably bonded 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 in a non-positive or positive manner. In particular, however, an integral connection, for example by gluing the electrode to the optical element or by vapor deposition of the electrode on the optical element, has proven to be particularly suitable. An integral formation of the electrode with the optical element can also be provided, for example by an additive manufacturing technique. The same fastening techniques can be provided for fastening the other electrode to the reference body.

According to a development of the invention, it can be provided that the electrode coupled to the optical element is fastened directly to the optical element.

In this way, deformations can be introduced into the optical element in an extremely targeted manner. However, it is not possible in this way to introduce global modes into the optical element, although this can be provided for various applications.

For this reason, in an alternative development of the invention, it can be provided that the electrode coupled to the optical element is connected indirectly to the optical element via an intermediate element spaced apart from the rear side of the optical element.

The fastening techniques already described in the context of fastening the electrode to the optical element can be provided in order to fasten the electrode to the intermediate element and/or to connect the intermediate element to the optical element.

The intermediate element can thus serve as a compensating plate and thereby make it possible to introduce global modes into the optical element or to deform the optical element in a “longer wavelength”. The deformation of the actuators can thus initially have a direct effect on the intermediate element and can then be passed on to the optical element via the intermediate element.

Depending on the application, a person skilled in the art may or may not provide an intermediate element and also vary the thickness and elasticity or the material properties of the intermediate element as required.

In a further development of the invention it can be provided that the intermediate element spacer elements and/or spacer struts arranged distributed along the back of the optical element are fastened to the optical element.

The fastening techniques already described in the context of fastening the electrode to the optical element can be provided in order to fasten the spacer elements/spacer struts to the optical element and/or to the intermediate element.

The influence of the actuators on the optical element via the intermediate element can be optimally adjusted by using spacer elements and/or spacer struts, for example by varying the geometry of the spacer elements or spacer struts and/or the material properties of the spacer elements or spacer struts.

For example, provision can be made for arranging individual spacer elements and/or spacer struts in the middle or centrally (with respect to the electrode surface) relative to the electrodes of a respective actuator.

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

The fastening techniques already described in the context of fastening the electrode to the optical element can be provided in order to fasten the bearing units/bearing struts to the optical element and/or to the intermediate element and/or to the reference body.

The electrodes of a respective actuator are preferably arranged between individual bearing units and/or bearing struts. In this way, a particularly advantageous force distribution can be made possible.

In a development of the invention, it can be provided that the spacer units or spacer struts are offset along the back of the optical element to the storage units or storage struts.

In this way, the optical element can be deformed over a wide range without there being any restrictions due to the mounting of the optical element on the reference body.

In an advantageous development of the invention, it can be provided that the electrode coupled to the optical element runs parallel to the rear side of the optical element.

In principle, however, an arrangement of the electrode relative to the rear side of the optical element that deviates from a parallel path can also be provided. However, a parallel course has proven to be particularly suitable and is technically relatively easy to implement.

In an advantageous development of the invention, it can be provided that the electrode coupled to the optical element (preferably the control electrode) is arranged on a side wall of a recess extending from the back into the optical element.

Optionally, it can additionally be provided that the electrode coupled to the reference body (preferably the reference electrode) is arranged on a projection that extends from the reference body into the recess of the optical element. The electrode coupled to the reference body can optionally also itself form the projection.

When extending into the recess or through the recess, the electrodes of the pair of electrodes are preferably arranged orthogonally or at least essentially orthogonally to the rear side and/or front side of the optical element in their basic state.

The recesses can in particular be slits with a small width, for example slits with a width of a few micrometers.

In the manner described it is possible, when the control voltage is applied, to generate forces within the recess and thus a deformation within the optical element, which in turn can lead to a deformation of the optically active front side of the optical element. In this way it is also possible to introduce global deformations into the optical element.

In an advantageous development of the invention, it can be provided that both electrodes of the electrode pair are mechanically coupled to the optical element and for this purpose are arranged on opposite side walls of a recess extending from the back into the optical element.

The two electrodes can, in particular, be vapour-deposited or glued onto the opposite side walls.

In a further development of the invention it can be provided that the dielectric is a liquid medium.

The liquid medium can preferably be distilled water or formamide. In principle, however, any dielectric media can be provided, in particular those with high dielectric strength and/or high permittivity.

The use of a liquid medium as a dielectric has proven to be particularly suitable.

In the case of a combination of different dielectrics, in particular different liquid media, it should be noted that the overall breakdown voltage can be determined by the dielectric layer in which the respective critical potential difference or field strength is reached first.

If a gaseous dielectric is provided, it can be sulfur hexafluoride (SF6), for example.

A high vacuum can also be advantageous.

According to a development of the invention, it can be provided that a fluidic connection is formed between the pairs of electrodes of adjacent actuators in order to enable an exchange of the liquid medium between the actuators.

In this way, in the case of incompressible liquid media, it can be ensured that these can flow out of the gap between the electrodes during actuation in order to enable the movement of the actuator.

The fluidic connection between the actuators can in particular be recesses, bores or the like in the bearing units and/or bearing struts, which preferably run between the individual actuators.

According to a further development, it can be provided that the optical assembly has at least one expansion tank which is fluidically connected to one of the actuators, to several of the actuators or to all of the actuators in order to allow the liquid medium to expand into the expansion tank.

The compensating tank can in particular be a compensating bellows which is able to correspondingly elastically expand depending on the amount of fluid medium taken up.

The expansion tank can ensure, among other things, that no deformation of the optical element occurs as a result of thermal expansion of the dielectric. The compensating tank, in particular the compensating bellows, is able to absorb excess liquid when there is thermal expansion of the liquid medium or when the gap between the electrodes of a common pair of electrodes is reduced due to the actuation.

In order to prevent crosstalk between the actuators, it can be advantageous to provide a separate expansion tank for each actuator or for individual groups of actuators.

According to one development, it can also be provided that the optical assembly has at least one inlet and at least one outlet for the liquid medium, which are fluidically connected to the actuators in such a way that the electrode pairs of the actuators can be flushed with the liquid medium.

In addition, a flow machine, for example a pump, can optionally be provided in order to allow the liquid medium to flow through.

The inflow can in particular be connected to an external liquid supply. In this case, a compensating tank can be dispensed with.

In an advantageous development of the invention, it can be provided that the electrodes of the pair of electrodes are arranged so as to run parallel to one another.

Optionally, however, it can also be provided that the electrodes of the electrode pair are arranged at an angle to one another. However, this is not preferred.

In an advantageous development of the invention, it can be provided that the actuators are distributed in a grid pattern along the rear side of the optical element.

Different deformation profiles can be set by distributing the actuators in a grid pattern. Preferably, the actuators are between those already described Storage units and / or storage struts arranged distributed.

The actuators can be arranged, for example, in segments of squares. Furthermore, there is the possibility of an arrangement in individual longitudinal slots in only one spatial direction. An arrangement in the form of triangles or some other grid-like arrangement can also be provided.

According to a development of the invention, the optical assembly can have a control device for generating the control voltages for the actuators in order to deform the optical element in a targeted manner.

The control device can be designed as a microprocessor. Instead of a microprocessor, any other device for implementing the control device can also be provided, for example 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 another programmable circuit, for example also a field programmable gate array (FPGA), a programmable logic array (PLA), and/or a commercial computer.

According to a development of the invention, it can be provided that the control device is set up to use the actuators as sensor units by excitation with the control voltage in a frequency range that is insignificant for the deformation operation, in order to detect an actual state of the deformation.

The actuators can thus optionally also be used as sensor units, in that conclusions can be drawn about the current actual state of the deformation via the electrical behavior of the two electrodes of the common pair of electrodes. The excitation with the control voltage for operation as a sensor unit can take place in the high-frequency range, for example in the range of a few megahertz. Since the control when used as actuators usually takes place in a bandwidth in the range of a few hundred Hertz, there is usually no mutual interference, so that actuator and sensor operation can take place in parallel.

The invention also relates to a method for deforming an optical element by means of a plurality of electrostatic actuators, each with a pair of electrodes made up of two electrodes spaced apart from one another. A control voltage is applied between the electrodes of the pair of electrodes in order to generate an electrostatic force, which is transmitted from the actuator to the optical element to deform the optical element. It is also provided that a dielectric is arranged between the electrodes of the electrode pair. A solid or liquid dielectric is preferably provided. However, a gaseous dielectric or a high vacuum can also be provided.

The use of the electrostatic actuators mentioned can be particularly advantageous, since in electrostatic actuators the force or expansion is not generated by the properties of the material itself, as is otherwise usual with piezoelectric or electrostrictive actuators, but is based on the attractive forces of electrical charges. The forces arising during actuation can thus be predicted and modeled much better.

A high-precision system can be provided by the proposed use of electrostatic actuators for deforming the optical element, since the electrostatic actuators have only very low non-reproducibility and their force effect can be significantly increased due to the proposed use of a dielectric between the electrodes of the electrode pair.

By applying the control voltage or the reference potential to the electrodes, either a tensile force or a compressive force can be generated between the electrodes involved. Provision is preferably made to generate a tensile force.

The invention also relates to a computer program product with program code means to carry out a method for deforming an optical element according to the above and following statements when the program is executed on a control device, in particular the control device of the optical assembly described above.

The invention is particularly suitable for use within the projection exposure system mentioned below or generally for use in lithography optics. In principle, however, the invention can be suitable for any application in which optical elements are to be deformed, in particular also for applications in aeronautics and space travel, astronomy and for military applications.

The invention also relates to a method for producing an optical assembly which has an optical element with an optically active front side and a back side facing away from the front side and a plurality of electrostatic actuators each having a pair of electrodes made up of two electrodes spaced apart from one another. The actuators are mechanically coupled to the back of the optical element in such a way that an electrostatic force generated between the electrodes of the electrode pair by means of an electrical control voltage can be transmitted to the optical element to deform the optical element. It is also provided that a dielectric is introduced between the electrodes of the electrode pair. A solid or liquid dielectric is preferably provided. However, a gaseous dielectric or a high vacuum can also be provided.

The one in the DE 10 2016 209 847 A1 The techniques described above for the mechanical connection between the optical element, the reference body, the intermediate element, the spacer elements/spacer struts, the storage units/storage struts and/or the electrodes can advantageously be used within the scope of the presently claimed invention. The revelation of the DE 10 2016 209 847 A1 is fully incorporated into the present specification by this reference.

In particular, it can be provided that the individual elements of the optical assembly are connected to one another by silicate or direct bonding or alternatively by an adhesive connection, a soldered connection or the like, in particular with regard to the connection between the bearing units/bearing struts and the optical element and/or the reference body .

The electrodes can be applied to the optical element, the reference body and/or the intermediate element, for example by vapor deposition of an electrically conductive layer. Other techniques for applying the electrodes can also be provided. In principle, any materially bonded, form-fitting and/or non-positive connection techniques can be possible.

The invention also relates to a projection exposure system for microlithography with an illumination system which has a radiation source, illumination optics and projection optics. The illumination optics and/or the projection optics have at least one optical assembly according to the statements above and below.

The invention is particularly suitable for correcting aberrations in the projection exposure system due to deformation of the optical element of the optical assembly.

The invention is suitable, inter alia, for use with a microlithographic DUV projection exposure system, but in particular for use with an EUV projection exposure system. A possible use of the invention also relates to immersion lithography.

Features that have been described in connection with one of the objects of the invention, namely given by the optical assembly, the method for deforming an optical element, the computer program product, the method for producing an optical assembly and the projection exposure system, are also applicable to the other objects of Invention advantageously implemented. Likewise, advantages that were mentioned in connection with one of the objects of the invention can also be understood in relation to the other objects of the invention.

In addition, it should be noted that terms such as "comprising", "having" or "with" do not exclude any other features or steps. Furthermore, terms such as "a" or "that" which indicate a singular number of steps or features do not exclude a plurality of features or steps - and vice versa.

In a puristic embodiment of the invention, however, it can also be provided that the features introduced in the invention with the terms “comprising”, “having” or “with” are listed exhaustively. Accordingly, one or more listings of features may be considered complete within the scope of the invention, e.g. considered for each claim. The invention can consist exclusively of the features mentioned in claim 1, for example.

It should be mentioned that designations such as “first” or “second” etc. are primarily used for reasons of distinguishing the respective device or method features and are not necessarily intended to indicate that features are mutually dependent or related to one another.

Furthermore, it should be emphasized that the values and parameters described here are deviations or fluctuations of ±10% or less, preferably ±5% or less, more preferably ±1% or less, and very particularly preferably ±0.1% or less of the respectively named Include value or parameter, provided that these deviations are not excluded in the implementation of the invention in practice. Specifying ranges by starting and ending values also includes all those values and fractions that are included in the specified range, in particular the start and end values and a respective mean value.

The invention also relates to an optical assembly independent of claim 1, comprising an optical element and at least one electrostatic actuator with at least two electrodes spaced apart from one another, the actuator being set up and mechanically coupled to the optical element in such a way that a generated between the electrodes of the actuator electrostatic force for deformation and / or alignment and / or positioning of the optical element is transferred to the optical element. The further features of claim 1 and the dependent claims as well as the features described in the present description relate to advantageous embodiments and variants of this optical assembly.

Exemplary embodiments of the invention are described in more detail below with reference to the drawing.

The figures each show preferred exemplary embodiments in which individual features of the present invention are shown in combination with one another. Features of an exemplary embodiment can also be implemented separately from the other features of the same exemplary embodiment and can accordingly easily be combined with features of other exemplary embodiments by a person skilled in the art to form further meaningful combinations and sub-combinations.

Elements with the same function are provided with the same reference symbols in the figures.

• 1 eine EUV-Projektionsbelichtungsanlage im Meridionalschnitt;
• 2 eine DUV-Projektionsbelichtungsanlage;
• 3 eine optische Baugruppe mit einem optischen Element, einem Bezugskörper und mehreren zwischen dem Bezugskörper und dem optischen Element angeordneten elektrostatischen Aktuatoren mit einem festen Dielektrikum in einer seitlichen Schnittdarstellung;
• 4 einen Ausschnitt einer Schnittdarstellung entlang der Schnittlinie IV der 3 zur Darstellung der rasterförmigen Anordnung der Aktuatoren entlang der Rückseite des optischen Elements;
• 5 eine optische Baugruppe gemäß einem weiteren Ausführungsbeispiel mit einem Zufluss und einem Abfluss für ein flüssiges Dielektrikum und einer fluidischen Verbindung zwischen den Aktuatoren in einer seitlichen Schnittdarstellung;
• 6 eine optische Baugruppe gemäß einem weiteren Ausführungsbeispiel mit einem Ausgleichsbehälter für ein flüssiges Dielektrikum und einer fluidischen Verbindung zwischen den Aktuatoren in einer seitlichen Schnittdarstellung;
• 7 eine optische Baugruppe gemäß einem weiteren Ausführungsbeispiel mit mehreren Ausgleichsbehältern für ein flüssiges Dielektrikum und einer fluidischen Verbindung zwischen den Aktuatoren in einer seitlichen Schnittdarstellung;
• 8 eine optische Baugruppe gemäß einem weiteren Ausführungsbeispiel mit einem Ausgleichsbehälter für ein flüssiges Dielektrikum, einer fluidischen Verbindung zwischen den Aktuatoren und einem zwischen den Aktuatoren und dem optischen Element angeordneten Zwischenelement in einer seitlichen Schnittdarstellung;
• 9 eine optische Baugruppe gemäß einem weiteren Ausführungsbeispiel mit innerhalb einer Ausnehmung in der Rückseite des optischen Elements angeordneten Elektroden in einem nicht ausgelenkten Zustand der Aktuatoren in einer seitlichen Schnittdarstellung;
• 10 die optische Baugruppe der 9 in einem ausgelenkten Zustand der Aktuatoren;
• 11 ein Beispiel für eine Rasteranordnung der Aktuatoren einer optischen Baugruppe gemäß 9;
• 12 ein Beispiel für eine weitere Rasteranordnung der Aktuatoren einer optischen Baugruppe gemäß 9; und
• 13 eine optische Baugruppe gemäß einem weiteren Ausführungsbeispiel mit innerhalb einer Ausnehmung in der Rückseite des optischen Elements angeordneten Elektroden in einer seitlichen Schnittdarstellung.

They show schematically:

• 1 an EUV projection exposure system in the meridional section;
• 2 a DUV projection exposure system;
• 3 an optical assembly with an optical element, a reference body and a plurality of electrostatic actuators arranged between the reference body and the optical element with a solid dielectric in a lateral sectional view;
• 4 a detail of a sectional view along the section line IV 3 to show the grid arrangement of the actuators along the back of the optical element;
• 5 an optical assembly according to a further embodiment with an inflow and an outflow for a liquid dielectric and a fluidic connection between the actuators in a lateral sectional view;
• 6 an optical assembly according to a further embodiment with an expansion tank for a liquid dielectric and a fluidic connection between the actuators in a lateral sectional view;
• 7 an optical assembly according to a further embodiment with multiple expansion tanks for a liquid dielectric and a fluidic connection between the actuators in a lateral sectional view;
• 8th an optical assembly according to a further exemplary embodiment with an expansion tank for a liquid dielectric, a fluidic connection between the actuators and an intermediate element arranged between the actuators and the optical element, in a lateral sectional view;
• 9 a side sectional view of an optical assembly according to a further exemplary embodiment with electrodes arranged within a recess in the rear side of the optical element in a non-deflected state of the actuators;
• 10 the optical assembly of the 9 in a deflected state of the actuators;
• 11 an example of a grid arrangement of the actuators of an optical assembly according to FIG 9 ;
• 12 an example of a further grid arrangement of the actuators of an optical assembly according to FIG 9 ; and
• 13 an optical assembly according to a further embodiment with electrodes arranged within a recess in the rear side of the optical element in a lateral sectional view.

The following are first with reference to 1 the essential components of an EUV projection exposure system 100 for microlithography are described by way of example. The description of the basic structure of the EUV projection exposure system 100 and its components should not be understood as limiting here.

In addition to a radiation source 102, an illumination system 101 of the EUV projection exposure system 100 has illumination optics 103 for illuminating an object field 104 in a Object level 105 on. In this case, 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 can be displaced via a reticle displacement drive 108, in particular in a scanning direction.

In 1 a Cartesian xyz coordinate system is drawn in for explanation. The x-direction runs perpendicularly into the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scan direction is in 1 along the y-direction. The z-direction runs perpendicular to the object plane 105.

The EUV projection exposure system 100 includes projection optics 109. The projection optics 109 are used to image the object field 104 in an image field 110 in an image plane 111. The image plane 111 runs parallel to the object plane 105. Alternatively, there is also an angle other than 0° between the object plane 105 and the image plane 111 is possible.

A structure on the reticle 106 is imaged onto a light-sensitive layer of a wafer 112 arranged in the region of the image field 110 in the image plane 111.

The wafer 112 is held by a wafer holder 113 . The wafer holder 113 can be displaced via a wafer displacement drive 114, in particular along the y-direction. The displacement of the reticle 106 via the reticle displacement drive 108 on the one hand and the wafer 112 on the other hand via the wafer displacement drive 114 can be synchronized with one another.

The radiation source 102 is an EUV radiation source. The radiation source 102 emits in particular EUV radiation 115, which is also referred to below as useful radiation or illumination radiation. The useful radiation 115 has, in particular, a wavelength in the range between 5 nm and 30 nm a DPP (Gas Discharged Produced Plasma) source. It can also be a synchrotron-based radiation source. The radiation source 102 can be a free-electron laser (FEL).

The illumination radiation 115 emanating from the radiation source 102 is bundled by a collector 116 . The collector 116 can be a collector with one or more ellipsoidal and/or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 116 can be used in grazing incidence ("Grazing Incidence", GI), i.e. with angles of incidence greater than 45°, or in normal incidence ("Normal Incidence", NI), i.e. with angles of incidence smaller than 45° of the illumination radiation 115 are applied. The collector 116 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation 115 and on the other hand to suppress stray light.

After the collector 116, the illumination radiation 115 propagates through an intermediate focus in an intermediate focal plane 117. The intermediate focal plane 117 can represent a separation between a radiation source module, comprising the radiation source 102 and the collector 116, and the illumination optics 103.

The illumination optics 103 includes a deflection mirror 118 and a first facet mirror 119 downstream of this in the beam path. The deflection mirror 118 can be a planar deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 118 can be designed as a spectral filter, which separates a useful light wavelength of the illumination radiation 115 from stray light of a different wavelength. If the first facet mirror 119 is arranged in a plane of the illumination optics 103 which is optically conjugate to the object plane 105 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 119 includes a multiplicity of individual first facets 120, which are also referred to below as field facets. Of these facets 120 are in the 1 only a few shown as examples.

The first facets 120 can be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 120 can be embodied as planar facets or alternatively as convexly or concavely curved facets.

Like for example from the DE 10 2008 009 600 A1 is known, the first facets 120 themselves can each also be composed of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 119 can be embodied in particular as a microelectromechanical system (MEMS system). For details refer to the DE 10 2008 009 600 A1 referred.

The illumination radiation 115 runs horizontally between the collector 116 and the deflection mirror 118, ie along the y-direction.

A second facet mirror 121 is arranged downstream of the first facet mirror 119 in the beam path of the illumination optics 103. If the second facet mirror 121 is arranged in a pupil plane of the illumination optics 103, it is also referred to as a pupil facet mirror. The second facet mirror 121 can also be arranged at a distance from a pupil plane of the illumination optics 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 A1 , the EP 1 614 008 B1 and the U.S. 6,573,978 .

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.

The second facets 122 can also be macroscopic facets, which can have round, rectangular or hexagonal borders, for example, or alternatively facets composed of micromirrors. In this regard, also on the DE 10 2008 009 600 A1 referred.

The second facets 122 can have plane or alternatively convexly or concavely curved reflection surfaces.

The illumination optics 103 thus forms a double-faceted system. This basic principle is also known as the "Fly's Eye Integrator".

It can be advantageous not to arrange the second facet mirror 121 exactly in a plane which is optically conjugate to a pupil plane of the projection optics 109 .

The individual first facets 120 are imaged in the object field 104 with the aid of the second facet mirror 121 . The second facet mirror 121 is the last beam-forming mirror or actually the last mirror for the illumination radiation 115 in the beam path in front of the object field 104.

In a further embodiment of the illumination optics 103 that is not shown, transmission optics can be arranged in the beam path between the second facet mirror 121 and the object field 104 , which particularly contribute to the imaging of the first facets 120 in the object field 104 . The transmission optics can have exactly one mirror, but alternatively also have two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 103 . The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirror, "normal incidence" mirror) and/or one or two mirrors for grazing incidence (GI mirror, "gracing incidence" mirror).

The illumination optics 103 has the version in which 1 shown, exactly three mirrors after the collector 116, namely the deflection mirror 118, the field facet mirror 119 and the pupil facet mirror 121.

In a further embodiment of the illumination optics 103, the deflection mirror 118 can also be omitted, so that the illumination optics 103 can then have exactly two mirrors downstream of the collector 116, namely the first facet mirror 119 and the second facet mirror 121.

The imaging of the first facets 120 by means of the second facets 122 or with the second facets 122 and transmission optics in the object plane 105 is generally only an approximate imaging.

The projection optics 109 includes a plurality of mirrors Mi, which are numbered consecutively according to their arrangement in the beam path of the EUV projection exposure system 100 .

At the in the 1 example shown, the projection optics 109 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 115. The projection optics 109 are doubly obscured optics. The projection optics 109 has an image-side numerical aperture which is greater than 0.5 and which can also be greater than 0.6 and which can be 0.7 or 0.75, for example.

Reflection surfaces of the mirrors Mi can be designed as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics 103, the mirrors Mi can have highly reflective coatings for the illumination radiation 115. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 109 has a large object image offset in the y-direction between a y-coordinate of a center of the object field 104 and a y-coordinate of the center of the image field 110. This object-image offset in the y-direction can be about as large like a z-distance between the object plane 105 and the image plane 111.

The projection optics 109 can in particular be anamorphic. In particular, it has different image scales βx, βy in the x and y directions. The two image scales βx, βy of the projection optics 109 are preferably at (βx, βy)=(+/−0.25, +/-0.125). A positive image scale β means an image without image reversal. A negative sign for the imaging scale β means imaging with image inversion.

The projection optics 109 thus leads to a reduction in the ratio 4:1 in the x-direction, ie in the direction perpendicular to the scanning direction.

The projection optics 109 lead to a reduction of 8:1 in the y-direction, ie in the scanning direction.

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

The number of intermediate image planes in the x-direction and in the y-direction in the beam path between the object field 104 and the image field 110 can be the same or, depending on the design of the projection optics 109, can be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions are known from U.S. 2018/0074303 A1 .

In each case one of the pupil facets 122 is assigned to precisely one of the field facets 120 in order to form a respective illumination channel for illuminating the object field 104 . In this way, in particular, lighting can result according to Köhler's principle. The far field is broken down into a large number of object fields 104 with the aid of the field facets 120 . The field facets 120 generate a plurality of images of the intermediate focus on the pupil facets 122 respectively assigned to them.

The field facets 120 are each imaged onto the reticle 106 by an associated pupil facet 122 in a superimposed manner in order to illuminate the object field 104 . In particular, the illumination of the object field 104 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

The illumination of the entrance pupil of the projection optics 109 can be geometrically defined by an arrangement of the pupil facets. The intensity distribution in the entrance pupil of the projection optics 109 can be set by selecting the illumination channels, in particular the subset of the pupil facets that guide light. This intensity distribution is also referred to as an illumination setting.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 103 can be achieved by redistributing the illumination channels.

Further aspects and details of the illumination of the object field 104 and in particular the entrance pupil of the projection optics 109 are described below.

The projection optics 109 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 109 cannot regularly be illuminated exactly with the pupil facet mirror 121 . When imaging the projection optics 109, which telecentrically images the center of the pupil facet mirror 121 onto the wafer 112, the aperture rays often do not intersect at a single point. However, a surface can be found in which the distance between the aperture rays, which is determined in pairs, is minimal. This surface represents the entrance pupil or a surface conjugate to it in position space. In particular, this surface shows a finite curvature.

The projection optics 109 may have different positions of the entrance pupil for the tangential and for the sagittal beam path. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 121 and the reticle 106 . With the help of this optical component, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

At the in the 1 The arrangement of the components of the illumination optics 103 shown is the pupil facet mirror 121 in a surface conjugate to the entrance pupil of the projection optics 109 arranged. The field facet mirror 119 is arranged tilted to the object plane 105 . The first facet mirror 119 is tilted relative to an arrangement plane that is defined by the deflection mirror 118 .

The first facet mirror 119 is tilted relative to an arrangement plane that is defined by the second facet mirror 121 .

In 2 an exemplary DUV projection exposure system 200 is shown. The DUV projection exposure system 200 has an illumination system 201, a device known as a reticle stage 202 for receiving and precisely positioning a reticle 203, by means of which the later structures on a wafer 204 are determined, a wafer holder 205 for holding, moving and precisely positioning the wafer 204 and an imaging device, namely projection optics 206, with a plurality of optical elements, in particular lenses 207, which are held in an objective housing 209 of the projection optics 206 via mounts 208.

As an alternative or in addition to the lenses 207 shown, various refractive, diffractive and/or reflective optical elements, including mirrors, prisms, end plates and the like, can be provided.

The basic functional principle of the DUV projection exposure system 200 provides that the structures introduced into the reticle 203 are imaged onto the wafer 204 .

The illumination system 201 provides a projection beam 210 in the form of electromagnetic radiation that is required for imaging the reticle 203 onto the wafer 204 . A laser, a plasma source or the like can be used as the source for this radiation. The radiation is shaped in the illumination system 201 via optical elements in such a way that the projection beam 210 has the desired properties in terms of diameter, polarization, shape of the wave front and the like when it strikes the reticle 203 .

An image of the reticle 203 is generated by means of the projection beam 210 and transmitted to the wafer 204 in a correspondingly reduced size by the projection optics 206 . The reticle 203 and the wafer 204 can be moved synchronously, so that areas of the reticle 203 are imaged onto corresponding areas of the wafer 204 practically continuously during a so-called scanning process.

Optionally, an air gap between the last lens 207 and the wafer 204 can be replaced by a liquid medium that has a refractive index greater than 1.0. The liquid medium can be, for example, ultrapure water. Such a structure is also referred to as immersion lithography and has an increased photolithographic resolution.

The use of the invention is not limited to use in projection exposure systems 100, 200, in particular not with the structure described. Furthermore, the invention and the following exemplary embodiments are not to be understood as being restricted to a specific design. The following figures represent the invention only by way of example and in a highly schematic manner.

A targeted deformation of its optical elements 118, 119, 120, 121, 122, Mi, 207 can be particularly suitable for correcting imaging errors in a projection exposure system, for example the projection exposure systems 100, 200. This is where the invention comes in.

In the 3 until 13 various exemplary embodiments of optical assemblies 1 according to the invention are shown as examples and in a highly schematic manner. The optical assemblies 1 enable a targeted deformation of optical elements 2, in particular for the correction of aberrations in a projection exposure system 100, 200. The optical elements 2 to be deformed can be arranged in particular within the illumination optics 103 and/or the projection optics 109, 206 of the projection exposure system 100, 200 be.

In the exemplary embodiments, the optical element 2 is shown as a mirror by way of example; however, this is not to be understood as limiting. The optical element 2 has an optically active front side 3 and a rear side 4 facing away from the front side 3 . The illumination radiation 115 or the projection beam 210 is influenced in a defined manner by the optically active front side 3 when impinging on the optical element 2, in particular in order to guide the beam path.

First, based on the 3 and 4 a first embodiment of the proposed optical assembly 1 will be described.

The optical assembly 1 has a plurality of electrostatic actuators 5 distributed along the rear side 4 of the optical element 2 . The actuators 5 can in particular be arranged in a grid pattern along the rear side 4 of the optical element 2, as can be seen particularly well from FIG 4 reveals. Each of the actuators 5 has an electrode pair consisting of two electrodes 6, 7 spaced apart from one another.

Preferably, the electrodes 6, 7 of the common pair of electrodes (in their non-deflected state) are arranged to run parallel to one another, as shown in all the exemplary embodiments. In principle, however, a tilted arrangement relative to one another can also be provided.

The actuators 5 are each set up and mechanically coupled to the rear side 4 of the optical element 2 in such a way that an electrostatic force generated between the electrodes 6, 7 of the pair of electrodes by means of an electrical control voltage U _1...n is applied to deform the optical element 2 on the optical element 2 is transmitted. For clarification is in the 3 as well as in the following 5 until 7 one of the actuators 5 is shown in a deflected state and the optical element 2 is thus shown in a partially deformed state.

A solid or liquid dielectric 8 is arranged between the electrodes 6, 7 of the pair of electrodes for a sufficiently high force effect and an increase in the dielectric strength between the electrodes 6, 7. If necessary, a gaseous dielectric 8 can also be provided, but preferably a gaseous dielectric 8 other than air 3 a solid medium is provided as the dielectric 8, which for the sake of illustration in 4 is hidden. In contrast, a liquid medium is provided in the following exemplary embodiments.

Preferably, the solid medium according to the embodiment of the 3 and 4 deformable to allow a reduction in the distance between the electrodes 6, 7 in the deflected state of the actuator 5. Alternatively, however, it can also be provided that the dielectric 8 does not completely fill the gap between the electrodes 6, 7. For example, it can be provided that the dielectric 8 is only arranged on one of the two electrodes 6, 7 or that the electrodes 6, 7 are coated with an insulating layer of the dielectric 8. In this way, too, the breakdown strength and the force of the actuator 5 can be increased.

In the exemplary embodiments, it is provided that one of the electrodes of the pair of electrodes is in the form of a control electrode 6 and the control voltage U _{1 . . . n} is applied thereto. The other electrode is embodied as a reference electrode 7 and, together with the further reference electrodes 7 of the other actuators 5, can be subjected to a common reference potential GND.

In the embodiments of 3 until 8th and 13, one of the electrodes 6, 7, preferably the reference electrode 7, is mechanically coupled to the rear side 4 of the optical element 2, as shown. The other electrode 6, 7, preferably the control electrode 6 as illustrated, is mechanically coupled to a reference body 9 spaced from the rear side 4 of the optical element 2. FIG.

The reference body 9 can be, for example, a mount for the optical element 2, a mounting frame for the optical element 2 or even the optical element 2 itself.

In the embodiments of 3 until 7 the reference body 9 is arranged via storage struts 10 distributed along the rear side 4 of the optical element 2 (cf. in particular also 4 ) attached to the optical element 2. The individual actuators 5 are arranged between the individual bearing struts 10 . The actuators 5 are in the embodiments of 3 until 8th aligned parallel to the rear side 4 of the optical element 2 .

To generate the control voltage U _1...n for the actuators 5, an in 3 Control device 11 shown in dashed lines may be provided. The control device 11 can be set up to deform the optical elements 2 in a targeted manner.

However, the control device 11 can also be set up to use the actuators 5 as sensor units by excitation with the control voltage U _{1 . . . n} in a frequency range that is insignificant for the deformation operation. In this way, an actual state of the deformation of the optical element 2 can be detected, for example in a higher frequency band. The method described above and below for deforming the optical element 2 can be carried out as a computer program product with program code means on the control device 11 .

Provision is preferably made for the dielectric 8 to be a liquid medium, in particular distilled water or formamide. A corresponding configuration is, for example, in 5 shown. In order to enable an exchange of the liquid medium between the actuators 5, between the pairs of electrodes of adjacent actuators 5 in the exemplary embodiments of FIG 5 until 13 each formed a fluidic connection. The fluidic connection between the actuators 5 is in the embodiments 5 until 8th through a respective bore 12 through the storage struts 10 reali Siert, which are arranged between the actuators 5. An inflow 13 and an outflow 14 for the liquid medium can be provided, which are fluidically connected to the actuators 5 in such a way that the electrode pairs of the actuators 5 are flushed with the liquid medium, as in FIG 5 implied. For this purpose, a flow machine, such as a pump, can be provided additionally or optionally (not shown).

In a particularly preferred embodiment, however, a closed system is provided, as shown in the following exemplary embodiments. In this case, provision can preferably be made to provide an expansion option for the liquid medium, in particular to enable thermally induced expansion and/or displacement of the dielectric 8 in the case of the deflected actuators 5 . In this regard, a compensating tank 15 can be provided, for example, which is fluidically connected to one of the actuators 5 in order to allow the liquid medium to expand (via the network of fluidic connections) into the compensating tank 15 . A compensating bellows is indicated in the figures by way of example. In order to enable the actuators 5 to be decoupled from one another, a plurality of equalizing tanks 15 can also be provided, for example one equalizing tank 15 for each actuator 5, as shown in FIG 7 implied.

At the in the 3 until 7 In the exemplary embodiments illustrated, one electrode 6 , 7 of the pair of electrodes, in this case the respective reference electrode 7 , is fastened directly to the optical element 2 . In this way, a local or short-wave deformation of the optical element 2 can be made possible, as indicated in the figures. However, if a global deformation or a longer-wave deformation is desired, it can be provided that the electrode 6, 7 (in particular the reference electrode 7) coupled to the optical element 2 is indirectly connected via an intermediate element 16 spaced from the rear side 4 of the optical element 2 the optical element 2 is connected. This is based on the 8th shown.

In this case, the reference body 9 can be fastened to the intermediate element 16 via the bearing struts 10 , the intermediate element 16 itself being fastened to the optical element 2 via spacer struts 17 distributed along the rear side 4 of the optical element 2 . The support struts 10 and the spacer struts 17 can be offset from one another along the rear side 4 of the optical element 2, with the spacer struts 17 being arranged on the optical element 2 as centrally as possible below the actuator surface or the electrode surface. In this way, the optical element 2 can be influenced in a particularly advantageous manner.

How based on the exemplary deflection of 8th can be seen, a certain decoupling of the individual actuators 5 from the optical element 2 can take place through the intermediate element 16, whereby a global deformation or a long-wave deformation of the optical element 2 is possible. This can be beneficial for some applications.

In the 9 until 12 an alternative embodiment of the optical assembly 1 is shown. 9 shows the optical assembly 1 in a non-deflected state of the actuators 5 and 10 in a purely exemplary and only to be understood schematically deflection of the actuators 5.

the 11 and 12 show possible grid arrangements for the distribution of the actuators 5 along the back 4 of the optical element 2. The in the 9 until 12 The variants shown are particularly suitable for a rectangular distributed arrangement (cf. 11 ) or for a line-like arrangement (cf. 12 ).

For the sake of a simpler representation, 9 until 13 the dielectric 8 hidden. Again, a liquid medium is preferably provided. The fluidic connection between the actuators 5 is in the embodiments 9 until 13 given by a corresponding spacing of the reference body 9 and a channel 18 formed therewith. A common expansion tank 15 is provided purely by way of example.

How based on the 9 and 10 results, both electrodes 6, 7 of the pair of electrodes can also be mechanically coupled to the optical element 2. For this purpose, the electrodes 6, 7 can be arranged in particular on opposite side walls of a recess 19, for example a slot, extending from the rear side 4 of the optical element 2. For example, the sidewalls may be coated (fully or partially) with a conductive medium. When the pairs of electrodes are subjected to a corresponding electrical control voltage U ₁ . Similar to the embodiment in 8th with the intermediate element 16, comparatively long-wave or global deformations can also be achieved in this way.

13 1 shows a further exemplary embodiment of an optical assembly 1. It is again provided that an electrode 7 is coupled to the optical element 2 and for this purpose is arranged on a side wall of a recess 19 extending from the rear side 4 into the optical element 2. In contrast, the electrode 6 coupled to the reference body 9 is arranged on a projection 20 extending from the reference body 9 into the recess 19 of the optical element 2 (or forms the projection 20 itself). In this way too, forces can advantageously be introduced directly into the optical element 2, in a similar way to the exemplary embodiment in FIG 9 and 10 is described. To provide the fluidic connection, bores 12 can be provided in the projection 20, in addition to a channel 18 between the actuators 5.

Optionally, in the embodiment of 13 , as shown, the force of a single actuator 5 can be further increased if two pairs of electrodes are provided instead of one pair of electrodes, the respective control electrodes 6 being electrically connected to one another, acted upon by the same control voltage U _1...n and each to one of the side walls of the recess 19 are aligned. In this way, the effective electrode area can be doubled.

Of course, a structure can also be provided in which the reference electrodes 7 project into the recess 19 starting from the reference body 9 .

Finally, it should be mentioned that the illustrated exemplary embodiments can in principle be combined with one another, provided this is not technically impossible. Further configurations of the actuators 5 and orientations/arrangements of the electrodes 6, 7 of the pair of electrodes can also be provided. In particular, the geometric relationships and orders of magnitude shown are purely schematic and exemplary and should not be understood to be true to scale.

A further possibility for increasing the electrostatic force can also be a toothing of the electrodes 6, 7 of a common pair of electrodes and/or a division of the individual electrodes 6, 7 into several individual electrodes.

QUOTES INCLUDED IN DESCRIPTION

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

Patent Literature Cited

• US 7692838 B2 [0011, 0012, 0014]
• DE 102016209847 A1 [0013, 0014, 0105]
• DE 102008009600 A1 [0132, 0136]
• US 2006/0132747 A1 [0134]
• EP 1614008 B1 [0134]
• US6573978 [0134]
• US 2018/0074303 A1 [0153]

Claims (26)

Optical assembly (1), having an optical element (2) with an optically active front (3) and a rear (4) facing away from the front (3) and a plurality distributed along the rear (4) of the optical element (2). Arranged electrostatic actuators (5) each having a pair of electrodes made of two spaced-apart electrodes (6, 7), wherein the actuators (5) are each set up and mechanically coupled to the rear side (4) of the optical element (2) such that a means an electrical control voltage (U _1...n ) between the electrodes (6, 7) of the pair of electrodes is transmitted to the optical element (2) for deformation of the optical element (2), characterized in that between the electrodes ( 6, 7) of the pair of electrodes, a dielectric (8) is arranged. Optical assembly (1) after claim 1 , characterized in that the dielectric (8) is a solid or a liquid dielectric (8). Optical assembly (1) after claim 1 or 2 , characterized in that the dielectric (8) has a permittivity greater than the permittivity of vacuum, preferably has a permittivity greater than the permittivity of air. Optical assembly (1) according to one of Claims 1 until 3 , characterized in that the dielectric (8) has a dielectric strength greater than the dielectric strength of air. Optical assembly (1) according to one of Claims 1 until 4 , characterized in that one of the electrodes of the pair of electrodes is designed as a control electrode (6) and can be acted upon by the control voltage (U _1...n ), and the other electrode is designed as a reference electrode (7) and together with the reference electrode (7) at least one of the other actuators (5) with a common reference potential (GND) can be applied. Optical assembly (1) according to one of Claims 1 until 5 , characterized in that one of the electrodes (6, 7) of the pair of electrodes is mechanically coupled to the back (4) of the optical element (2) and the other electrode (7, 6) to one of the back (4) of the optical element (2) spaced reference body (9) is mechanically coupled. Optical assembly (1) after claim 6 , characterized in that the with the optical element (2) coupled electrode (6, 7) is attached directly to the optical element (2). Optical assembly (1) after claim 6 , characterized in that the electrode (6, 7) coupled to the optical element (2) is connected indirectly to the optical element (2) via an intermediate element (16) at a distance from the back (4) of the optical element (2). Optical assembly (1) after claim 8 , characterized in that the intermediate element (16) is attached to the optical element (2) via spacer elements and/or spacer struts (17) distributed along the rear side (4) of the optical element (2). Optical assembly (1) according to one of Claims 6 until 9 , characterized in that the reference body (9) is attached to the optical element (2) or to the intermediate element (16) via bearing units and/or bearing struts (10) distributed along the back (4) of the optical element (2). Optical assembly (1) after claim 9 and 10 , characterized in that the spacer units or spacer struts (17) are offset along the back (4) of the optical element (2) to the storage units or storage struts (10). Optical assembly (1) according to one of Claims 6 until 11 , characterized in that the with the optical element (2) coupled electrode (6, 7) runs parallel to the back (4) of the optical element (2). Optical assembly (1) according to one of Claims 6 until 11 , characterized in that with the optical element (2) coupled electrode (6, 7) on a side wall of a starting from the back (4) in the optical element (2) extending recess (19) is arranged, wherein the with the electrode (7, 6) coupled to the reference body (9) is arranged on a projection (20) extending from the reference body (9) into the recess (19) of the optical element (2). Optical assembly (1) according to one of Claims 1 until 5 , characterized in that both electrodes (6, 7) of the electrode pair are mechanically coupled to the optical element (2) and for this purpose on opposite side walls of a recess (19) extending from the back (4) into the optical element (2). are arranged. Optical assembly (1) according to one of Claims 1 until 14 , characterized in that the dielectric (8) is a liquid medium, preferably distilled water or formamide. Optical assembly (1) after claim 15 , characterized in that a fluidic connection is formed between the pairs of electrodes of adjacent actuators (5) in order to enable an exchange of the liquid medium between the actuators (5). Optical assembly (1) after claim 15 or 16 characterized by at least one expansion tank (15) which is fluidically connected to one of the actuators (5), to several of the actuators (5) or to all actuators (5) in order to allow the liquid medium to expand into the expansion tank (15). enable. Optical assembly (1) according to one of Claims 15 until 17 characterized by at least one inflow (13) and at least one outflow (14) for the liquid medium, which are fluidically connected to the actuators (5) in such a way that the electrode pairs of the actuators (5) can be flushed by the liquid medium. Optical assembly (1) according to one of Claims 1 until 18 , characterized in that the electrodes (6, 7) of the pair of electrodes are arranged to run parallel to one another. Optical assembly (1) according to one of Claims 1 until 19 , characterized in that the actuators (5) along the back (4) of the optical element (2) are distributed in a grid. Optical assembly (1) according to one of Claims 1 until 20 , characterized by a control device (11) for generating the control voltages (U _{1 ... n} ) for the actuators (5) in order to deform the optical element (2) in a targeted manner. Optical assembly (1) after Claim 21 , characterized in that the control device (11) is set up to use the actuators (5) by excitation with the control voltage (U _{1 ... n} ) in a non-essential for the deformation operation frequency range as sensor units to an actual state of detect deformation. Method for deforming an optical element (2) by means of a plurality of electrostatic actuators (5), each with a pair of electrodes consisting of two spaced-apart electrodes (6, 7), after which a control voltage (U _{1.. .n} ) is applied in order to generate an electrostatic force which is transmitted from the actuator (5) to the optical element (2) to deform the optical element (2), characterized in that between the electrodes (6, 7) of the pair of electrodes, a dielectric (8) is arranged. Computer program product with program code means in accordance with a method for deforming an optical element (2). Claim 23 to be carried out when the program is executed on a control device (11). Method for producing an optical assembly (1) comprising an optical element (2) with an optically active front side (3) and a rear side (4) facing away from the front side (3) and a plurality of electrostatic actuators (5), each with a pair of electrodes of two spaced-apart electrodes (6, 7), after which the actuators (5) are mechanically coupled to the back (4) of the optical element (2) in such a way that a means of an electrical control voltage (U _{1 ... n} ) between The electrostatic force generated by the electrodes (6, 7) of the pair of electrodes can be transferred to the optical element (2) to deform the optical element (2), characterized in that a dielectric (8) is introduced between the electrodes (6, 7) of the pair of electrodes becomes. Projection exposure system (100, 200) for microlithography with an illumination system (101, 201) which has a radiation source (102), illumination optics (103) and projection optics (109, 206), the illumination optics (103) and/or the Projection optics (109, 206) at least one optical assembly according to one of Claims 1 until 22 having.

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