OPTICAL SYSTEM AND LITHOGRAPHY APPARATUS

Abstract

An optical system comprises at least one mirror having a mirror body and a mirror surface, and at least one actuator device coupled to the mirror body and serving for deforming the mirror surface. The actuator device comprises at least one electrostrictive actuator element for generating a mechanical stress in the mirror body for deforming the mirror surface depending on an electrical drive voltage, and at least one electrostrictive sensor element for outputting a sensor signal depending on a deformation of the sensor element. The at least one sensor element is arranged directly adjacent to the actuator element and/or is arranged in such a way that it is configured at least partly for transferring the mechanical stress generated by the actuator element to the mirror body.

Claims

1. An optical system, comprising: a mirror, comprising: a mirror body; and a mirror surface; and an actuator device configured to deform the mirror surface, the actuator device comprising: an electrostrictive actuator element configured to produce mechanical stress in the mirror body to deform the mirror surface depending on an electrical drive voltage; an electrostrictive sensor element configured to output a sensor signal depending on a deformation of the electrostrictive sensor element, wherein: at least one of the following holds: the electrostrictive sensor element directly adjoins the electrostrictive actuator element; the electrostrictive sensor element is supported by a side of the mirror body facing away from the mirror surface and is separated from the mirror body by at least the electrostrictive actuator element; the electrostrictive sensor element is configured to at least partially set up to transfer the mechanical stress produced by the electrostrictive actuator element to the mirror body; and the actuator device is coupled to the mirror body so that the mirror surface is deformable depending on the electrical drive voltage; and the electrostrictive actuator element is supported by a side of the mirror body facing away from the mirror surface.

2. The optical system of claim 1, further comprising a closed-loop control unit configured to control the drive voltage depending on the sensor signal so that a predetermined mechanical stress in the mirror body is achieved.

3. The optical system of claim 2, wherein the actuator device comprises an assignment unit configured to assign a value of the output sensor signal to an achieved deformation of the mirror surface based on a calibration measurement, and the closed-loop control unit is configured to control the drive voltage depending on the assigned value and a predetermined deformation of the mirror surface.

4. The optical system of claim 1, wherein the electrostrictive actuator element and the electrostrictive sensor element define a monolithic element.

5. The optical system of claim 1, wherein the electrostrictive actuator element and the electrostrictive sensor element are integrated in a layer supported by the mirror on a side of the mirror body facing away from the mirror surface.

6. The optical system of claim 1, wherein, in a direction along a surface normal of the mirror surface, the electrostrictive sensor element is at least partially between the electrostrictive actuator element and the mirror body.

7. The optical system of claim 1, wherein the electrostrictive actuator element and the electrostrictive sensor element each comprises a layer comprising electrostrictive material.

8. The optical system of claim 7, wherein the electrostrictive actuator element comprises a plurality of layers comprising electrostrictive material, each layer comprises an assigned cathode and an assigned anode, and each layer is drivable with a respective drive voltage.

9. The optical system of claim 7, wherein the electrostrictive actuator element and the electrostrictive sensor element define a layer stack comprising at least two layers.

10. The optical system of claim 1, wherein: the actuator device comprises at least electrostrictive sensor elements; material compositions of the at least two electrostrictive sensor elements differ from each other; and each of the at least two electrostrictive sensor elements is configured to output a sensor signal.

11. The optical system of claim 10, further comprising an ascertainment unit configured to ascertain a temperature in the mirror body depending on the sensor signals output by the at least two electrostrictive sensor elements.

12. The optical system of claim 10, further comprising a measurement unit configured to apply a measurement alternating voltage to the at least two electrostrictive sensor elements to generate the sensor signals output by the electrorestrictive sensor elements, wherein a frequency of the measurement alternating voltage is different for each of the at least two electrostrictive sensor elements.

13. The optical system of claim 1, wherein: the actuator device comprises a plurality of M electrostrictive actuator elements; the actuator device comprises a plurality of N electrorestrictive sensor elements; M is an integer; N is an integer; and the electrostrictive actuator elements and the electrostrictive sensor elements are disposed in alternation.

14. The optical system of claim 1, comprising a plurality of individually controllable actuator devices supported by the mirror.

15. An apparatus, comprising: an optical system according to claim 1, wherein the apparatus is a lithography apparatus.

16. The apparatus of claim 15, comprising: an illumination system; and a projection system.

17. The apparatus of claim 16, wherein the projection system comprises the optical system.

18. A method, comprising: providing an optical system according to claim 1; using the optical system to deform the mirror surface.

19. A method of operating an optical system comprising a mirror which comprises a mirror body and a mirror surface, the optical system further comprising an actuator device supported by a side of the mirror body facing away from the mirror surface, the method comprising: driving an electrostrictive actuator element of the actuator device with an electrical drive voltage so that a mechanical stress is produced in the mirror body and the mirror surface deforms; using an electrorestrictive sensor element of the actuator device to detect a sensor signal depending on a deformation of the electrostrictive sensor element; and determining the deformation of the mirror surface depending on the detected sensor signal, wherein at least one of the following holds: the electrostrictive sensor element directly adjoins the electrostrictive actuator element; the electrostrictive sensor element is supported by a side of the mirror body facing away from the mirror surface and is separated from the mirror body by at least the electrostrictive actuator element; and the electrostrictive sensor element is configured to at least partially set up to transfer the mechanical stress produced by the electrostrictive actuator element to the mirror body.

20. The method of claim 19, wherein a lithography apparatus comprises the optical system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] In the figures:

[0079] FIG. 1 shows a schematic view of a first exemplary embodiment of an optical system;

[0080] FIG. 2 shows a schematic view of a first exemplary embodiment of an arrangement of a mirror with an actuator device;

[0081] FIG. 3 shows a schematic view of a second exemplary embodiment of an arrangement of a mirror with an actuator device;

[0082] FIG. 4 shows a schematic view of a third exemplary embodiment of an arrangement of a mirror with an actuator device;

[0083] FIG. 5 shows a schematic view of a fourth exemplary embodiment of an arrangement of a mirror with an actuator device;

[0084] FIG. 6 shows a schematic view of a fifth exemplary embodiment of an arrangement of a mirror with an actuator device;

[0085] FIG. 7 shows a schematic view of a sixth exemplary embodiment of an arrangement of a mirror with an actuator device;

[0086] FIG. 8 shows a schematic view of a seventh exemplary embodiment of an arrangement of a mirror with an actuator device having two sensor elements;

[0087] FIG. 9 shows a schematic view of an exemplary embodiment of a construction of an actuator element;

[0088] FIG. 10 shows a schematic view of an exemplary embodiment of a drive for a plurality of actuator elements and sensor elements in an actuator device;

[0089] FIG. 11 shows three graphs of a behavior of physical variables as a function of a drive voltage;

[0090] FIG. 12 is a graph showing a plurality of curves of the dielectric susceptibility as a function of a drive voltage;

[0091] FIG. 13 shows a schematic block diagram of an exemplary embodiment of a closed-loop control circuit;

[0092] FIG. 14A shows a schematic view of an embodiment of an EUV lithography apparatus;

[0093] FIG. 14B shows a schematic view of an embodiment of a DUV lithography apparatus; and

[0094] FIG. 15 shows a schematic block diagram of an exemplary embodiment of a method for correcting an aberration in an optical system.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0095] Unless indicated otherwise, elements that are the same or functionally the same have been given the same reference signs in the figures. It should also be noted that the illustrations in the figures are not necessarily true to scale.

[0096] FIG. 1 shows a schematic view of a first exemplary embodiment of an optical system 200. The optical system 200 here comprises a light source LS, a lens element 128 which collimates the light incident thereon from the light source LS, two mirrors 110, 210, a further lens element 128 and a wafer 124 or object slide on which the light from the further lens element 128 is focused. For example, the optical system 200 is an illumination system of a microscope or a lithography apparatus 100A, 100B (see FIGS. 14A, 14B).

[0097] The second mirror 210 of the optical system 200 comprises a mirror body 212, on the front side of which the mirror surface 214 is arranged. An actuator device 220 is arranged on the rear side of the mirror body 212 and is set up to deform the mirror surface 214 by coupling a mechanical stress into the mirror body 212. Without restricting the generality, only one actuator device 220 is shown here and also in the following figures. However, it goes without saying that a plurality of such actuator devices 220 can be arranged at the mirror 210 in order to deform the mirror surface 214 in a targeted manner with a high spatial resolution and/or to achieve an overall deformation of the mirror 210.

[0098] Due to the fact that the mirror surface 214 of the mirror 210 can be deformed, it is possible to compensate for an aberration, i.e. an imaging error. In this case, the imaging error is dependent for example on an operating state of the optical system 200 and/or of further optical systems which are coupled to the optical system 200. For example, spatial and/or temporal temperature differences and/or temperature fluctuations can be compensated for by the actuator device 220. It is therefore also possible to speak of an adaptive optical system 200 whose state is subject to closed-loop control or kept constant in relation to a reference state. The actuator device 220 can comprise a closed-loop control circuit for controlling the actuator element 222 (see FIG. 2-8, 10, 13, 14A or 14B).

[0099] The precise mode of operation of the actuator device 220 will be explained in detail with reference to the following figures.

[0100] FIGS. 2-7 each show a schematic view of an exemplary embodiment of an arrangement of a mirror 210 with an actuator device 220. The exemplary embodiments differ in terms of the specific arrangement of the actuator device 220 and mirror 210. Each of the exemplary embodiments may be used in an optical system 200, as shown in FIGS. 1, 14A and 14B.

[0101] FIG. 2 shows an actuator device 220 which is arranged between the mirror body 212 and a mirror carrier 216. The mirror carrier 216 forms a mechanical fixed point, which means it is rigid and fixed. The actuator device 220 has an actuator element 222 and a sensor element 224, wherein the sensor element 224 makes mechanical contact with the mirror body 212 and the actuator element 222 is supported on the mirror carrier 216. Furthermore, a drive unit 226 is present, which provides the drive voltage VS for driving the actuator element 222. In this example, the drive unit 226 also detects the sensor signal SS output by the sensor element 224. The drive unit 226 can be designed as a closed-loop control unit, or comprises one, which controls the drive voltage VS in dependence on the sensor signal SS.

[0102] In this arrangement, the actuation direction 223 is parallel to a surface normal of the mirror surface 214. The actuator element 222 stretches or expands in the actuation direction 223 when a drive voltage VS is applied to it. A stretching of the actuator element 222 leads to a bulging or displacement of the mirror surface 214 at the location of the actuator device 220 because the mirror carrier 216 is fixed. It is possible here for the mirror body 212 to be supported on the mirror carrier 216 at one or more points with a fixed connecting element (not shown). Such a fixed connecting element fixes where it is arranged the distance between the mirror body 212 and the mirror carrier 216, for example.

[0103] FIG. 3 shows an alternative embodiment of an actuator device 220 which is arranged between the mirror body 212 and a mirror carrier 216. In this case, the sensor element 224 is arranged laterally directly on the actuator element 222. In this arrangement, the sensor element 224 will exactly follow any deformation, for example stretching or compression, of the actuator element 222 along the actuation direction 223. The actual deformation of the actuator element 222 can therefore be determined very precisely from the sensor signal SS.

[0104] FIGS. 4 to 7 each show a different integration of the actuator device 220, wherein, in contrast to FIGS. 2 and 3, a transverse actuation direction 223, i.e. in the plane of the mirror body 212, is used. In FIGS. 4 and 5, the actuator device 220 is adhesively bonded to the rear side of the mirror body 212 or is firmly connected thereto in a similar manner. The sensor element 224 is either arranged between the actuator element 222 and the mirror body 212 (FIG. 4) or arranged on the rear side of the actuator element 222 (FIG. 5). In the arrangement shown in FIG. 4, the sensor element 224 transfers any mechanical stress produced by the actuator element 222 to the mirror body 212. For example, the sensor element 224 undergoes the same deformation as the actuator element 222 and the region of the mirror body 212 in direct contact with the sensor element 224. The transverse actuation 223, which can be a stretching or a shortening in relation to the actuator element 222, produces mechanical stress in the mirror body 212, as a result of which the mirror surface 214 is correspondingly deformed.

[0105] In the exemplary embodiments in FIGS. 6 and 7, the actuator element 222 and the sensor element 224 are embedded in a matrix MX. The matrix MX comprises for example a material of the same material class as the actuator element 222, and the sensor element 224 can comprise of an electrostrictive ceramic material. Advantageously, the actuator element 222, the sensor element 224 and the matrix MX form a substantially homogeneous material layer 221, which is fixed two-dimensionally to, optionally over the whole area of, the rear side of the mirror body 212. The active regions of the actuator element 222 and the sensor element 224 are defined by the arrangement of electrodes in the material MX. In these embodiments, a mechanical coupling of the actuator element 222 to the mirror body 212 can be particularly strong, which has an advantageous effect on the maximum deformation of the mirror surface 214 that is achievable.

[0106] The exemplary embodiments shown in FIGS. 2-7 can also be combined with one another as desired.

[0107] FIG. 8 shows a schematic view of a fourth exemplary embodiment of an arrangement of a mirror 210 with an actuator device 220. The basic arrangement corresponds to that shown in FIG. 7, wherein the actuator device 220 here has two sensor elements 224 which enclose the actuator element 222 in the manner of a sandwich. The two sensor elements 224 advantageously have different chemical compositions, which means they have different dependencies on the temperature and the deformation. Then it is possible to ascertain from the two sensor signals SS not only the deformation of the respective sensor element 224 but also the temperature. In the present case, this is done by an ascertainment unit 230 that is especially set up for this purpose.

[0108] FIG. 9 shows a schematic view of an exemplary embodiment of a construction of an actuator element 222, which here comprises a plurality of individual layers L1-Ln. An electrode A1 is arranged on the uppermost layer L1 and is operated here, for example, as an anode. A further electrode K1, which is operated here as a cathode, is arranged between the uppermost layer L1 and the layer L2 arranged therebelow in an adjoining manner. The anode A1 and the cathode K1 can be said to enclose the top layer L1 in the manner of a sandwich. A drive voltage VS applied between the anode A1 and cathode K1 (see FIG. 2-8 or 10-13) leads to the formation of an electric field in the layer L1. The roles of the anode A1 and the cathode K1 can also be reversed in embodiments, in which case the direction of the electric field is reversed.

[0109] An electrode A2, which is operated as an anode, is again arranged between the second layer from the top L2 and the third layer from the top L3. It can be seen here that the cathode K1 forms a common cathode for the adjoining layers L1 and L2. The anode A2 also forms a common anode for the adjoining layers L2 and L3.

[0110] In this example, this layered construction is continued until the desired number of layers has been reached. Arranged underneath the bottom layer Ln is a terminating electrode Kn, which in this embodiment operates as a cathode. In this alternating construction with common electrodes A1-An, K1-Kn, the electrostrictive material is for example one in which the mechanical strain is proportional to the square of the polarization, so that the layers L1-Ln, despite different directions of the electric field, produce a deformation in the same direction.

[0111] In other embodiments in which an electrostrictive material is used in which the mechanical strain is proportional to the polarization, the electrodes A1-An, K1-Kn should be arranged and driven in such a way that the electric field in all layers L1-Ln points in the same direction, since otherwise the layers L1-Ln work against one another.

[0112] A layer thickness of the layers L1-Ln can be different for each layer L1-Ln. The layer thicknesses of the different layers L1-Ln can be substantially the same and selected from a range of 10 μm-500 μm. In this case, a material composition can likewise be selected differently for each of the layers L1-Ln, for example in order to attain different electrostrictive properties.

[0113] In further embodiments, a sensor element 224 has such a layered construction as is shown in FIG. 9 for an actuator element 222. In this case, the use of different chemical compositions for different layers L1-Ln for example has the advantage that a comparison of the sensor signals SS of the individual layers L1-Ln can be used to draw conclusions not only regarding the mechanical stress but also regarding further influencing variables, for example the temperature in the layers L1-Ln.

[0114] FIG. 10 shows a schematic view of an exemplary embodiment of an actuator device 220 that comprises a plurality of actuator elements 222, a plurality of sensor elements 224 and a drive unit 226. Three sensor elements 224 and two actuator elements 222 which form a layer stack are provided in this case, wherein the actuator elements 222 each comprise, for example, three layers L1-L3 made of electrostrictive material.

[0115] Two of the sensor elements 224 enclose the entire layer stack in the manner of a sandwich, and the third sensor element 224 divides the layer stack in the middle. In the present case, passive regions are respectively arranged between the sensor elements 224 and the actuator elements 222. These can also be omitted in embodiments, wherein an electrode arranged between the sensor element 224 and actuator element 222 then constitutes a common electrode. The common electrode in this case can be grounded because the sensor element is advantageously operated without bias voltage.

[0116] The drive unit 226 here comprises a voltage source that is subject to closed-loop control for providing the drive voltage VS for the actuator elements 222 and three measurement units that are set up to generate the sensor signal SS of a respective sensor element 224 via a measurement alternating voltage VM. The measurement alternating voltages VM can have different frequencies in order to avoid mutual interference. In further specific embodiments, the multiple actuator elements 222 can also be operated with different drive voltages VS.

[0117] FIG. 11 shows three diagrams of a behavior of physical variables, the mechanical stress a, the gradient of the deflection e achieved in relation to the drive voltage VS, ∂e/∂VS, and the dielectric susceptibility x as a function of a drive voltage VS for an exemplary electrostrictive layer, which can be used in an actuator element 222 (see FIG. 2-10 or 13) or a sensor element 224 (see FIG. 2-8, 10 or 13). The variables σ, e and χ are indicated in arbitrary units. The unit volt is selected as the scale for the drive voltage VS. The electrostrictive material is for example a material with a composition PMN.sub.xPt.sub.1−x. The curves shown relate to a mechanically free state of the layer, i.e. a state without mechanical prestressing and without the layer being embedded in a rigid material system.

[0118] The top diagram shows the mechanical stress σ (unit: N/m.sup.2 or Pa) which is provided or produced by the layer driven with the drive voltage VS. For a drive voltage VS=0, the layer does not produce any mechanical stress σ. It can likewise be seen that a small drive voltage VS brings about only very little mechanical stress σ. In the case of low drive voltages VS, the mechanical stress σ produced is, for example, proportional to the square of the drive voltage VS.

[0119] The middle diagram shows the gradient of the deflection e achieved in relation to the drive voltage VS as a function of the drive voltage VS.

[0120] The bottom diagram shows the dielectric susceptibility x as a function of the drive voltage VS. It can be seen that the dielectric susceptibility x has a maximum at a drive voltage VS=0.

[0121] As shown in FIG. 12, the dielectric susceptibility x at the drive voltage VS=0 furthermore has a very high sensitivity with regard to mechanical stress. FIG. 12 shows a diagram with a plurality of curves of the dielectric susceptibility x as a function of a drive voltage VS. The five curves 1-5 shown differ with regard to a deformation of the layer. For example, curve 3 corresponds to the mechanically free or unstressed state. Curves 1 and 2 correspond, for example, to a stretching of the layer in the ppm range, for example 10 ppm for curve 1 and 5 ppm for curve 2. Curves 4 and 5 correspond, for example, to a compression of the layer in the ppm range, for example 5 ppm for curve 4 and 10 ppm for curve 5. Due to this sensitivity maximum of the dielectric susceptibility x, this physical variable is particularly well suited as a measurement variable to determine a deformation of the layer, for example in a sensor element 224. The dielectric susceptibility x can be determined by an impedance measurement via the measurement alternating voltage VM.

[0122] FIG. 13 shows a schematic block diagram of an exemplary embodiment of a closed-loop control circuit in an actuator device 220. In the present case, the drive unit 226 is designed as a closed-loop control unit. The closed-loop control unit 226 receives a predetermined mechanical target stress σ.sub.s from the outside, for example by way of a control computer (not shown), which the actuator device 220 is intended to provide or produce via the actuator element 222. The closed-loop control unit 226 then drives the actuator element 222 with the drive voltage VS. The drive voltage VS can be selected in such a way that, under good conditions, it exactly achieves the mechanical target stress σ.sub.s, which is known, for example, from characterization measurements of the actuator element 222. However, due to hysteresis or various ambient influences, the actuator element 222 may slightly miss the target mechanical stress σ.sub.s.

[0123] The sensor element 224 is deformed with the actuator element 222. The extent of the deformation can be ascertained as described above, which is represented here by the sensor signal SS. The sensor signal SS is for example characteristic of the deformation of the sensor element 224 and thus also of the mechanical stress σ achieved in the sensor element 224. Due to the direct coupling of the sensor element 222 to the actuator element 224, the mechanical stress σ in the sensor element 224 substantially corresponds to that in the actuator element 222. The sensor signal SS is therefore suitable as a closed-loop control signal. The closed-loop control unit 226 will therefore readjust the drive voltage VS for the actuator element 222 on the basis of the sensor signal SS.

[0124] A closed-loop control cycle can last for example in the range from 1 ms-100 ms, corresponding to a closed-loop control frequency of between 10 Hz-1 kHz.

[0125] FIG. 14A shows a schematic view of an EUV lithography apparatus 100A, which comprises a beam shaping and illumination system 102 and an optical system 200, which is embodied here as a projection system. In this case, EUV stands for “extreme ultraviolet” and denotes a wavelength of the working light of between 0.1 nm and 30 nm. The beam shaping and illumination system 102 and the projection system 200 are respectively provided in a vacuum housing (not shown), wherein each vacuum housing is evacuated with the aid of an evacuation apparatus (not shown). The vacuum housings are surrounded by a machine room (not shown), in which driving apparatuses for mechanically moving or setting optical elements are provided. Furthermore, electrical controllers and the like may also be provided in the machine room.

[0126] The EUV lithography apparatus 100A has an EUV light source 106A. A plasma source (or a synchrotron), which emits radiation 108A in the EUV range (extreme ultraviolet range), that is to say for example in the wavelength range of 5 nm to 20 nm, can for example be provided as the EUV light source 106A. In the beam shaping and illumination system 102, the EUV radiation 108A is focused and the desired operating wavelength is filtered out from the EUV radiation 108A. The EUV radiation 108A produced by the EUV light source 106A has a relatively low transmissivity through air, for which reason the beam guiding spaces in the beam shaping and illumination system 102 and in the projection system 200 are evacuated.

[0127] The beam shaping and illumination system 102 illustrated in FIG. 14A has five mirrors 110, 112, 114, 116, 118. After passing through the beam shaping and illumination system 102, the EUV radiation 108A is guided onto a photomask (reticle) 120. The photomask 120 is likewise designed as a reflective optical element and can be arranged outside the systems 102, 104. Furthermore, the EUV radiation 108A may be directed onto the photomask 120 via a mirror 122. The photomask 120 has a structure which is imaged onto a wafer 124 or the like in a reduced fashion via the projection system 200.

[0128] The projection system 200 (also referred to as a projection lens) has five mirrors M1 to M5 for imaging the photomask 120 onto the wafer 124. In this case, individual mirrors M1 to M5 of the projection system 200 may be arranged symmetrically in relation to an optical axis 126 of the projection system 200. It should be noted that the number of mirrors M1 to M5 of the EUV lithography apparatus 100A is not restricted to the number shown. A greater or lesser number of mirrors M1 to M5 may also be provided. Furthermore, the mirrors M1 to M5 are generally curved on their front sides for beam shaping.

[0129] The projection system 200 furthermore has a further mirror 210, on the rear side of which a multiplicity of actuator devices 220 are arranged, each of which can be designed as shown by FIG. 2-8, 10 or 13. Each actuator device 220 comprises an assigned actuator element 222 and an assigned sensor element 224. A drive unit 226 is set up to drive the actuator elements 222 with a drive voltage VS and to apply a measurement alternating voltage VM to the sensor elements 224 in order to generate a respective sensor signal SS. For the sake of clarity, only one drive unit 226 is shown here, which drives all the actuator elements 222 and sensor elements 224. The front side of the mirror 210 can be deformed by targeted driving of the actuator devices 220, which can be used to correct optical aberrations to increase the resolution of the lithography process.

[0130] In advantageous embodiments, the actuation is controlled with closed-loop control by the actuator elements 222 by virtue of the fact that an actually achieved deformation is detected by the sensor elements 224 and the drive voltage VS can therefore be controlled with closed-loop control by evaluating the sensor signal SS. This closed-loop control takes place individually for each actuator device 220, wherein only one actuator device 220 and only one drive voltage VS, one measurement alternating voltage VM and one sensor signal SS are shown for reasons of clarity.

[0131] The projection system 200, or also the beam shaping and illumination system 102, can have further mirrors 210 with an assigned actuator device 220.

[0132] FIG. 14B shows a schematic view of a DUV lithography apparatus 100B, which comprises a beam shaping and illumination system 102 and an optical system 200, which is designed here as a projection system. In this case, DUV stands for “deep ultraviolet” and denotes a wavelength of the working light of between 30 nm and 250 nm. As has already been described with reference to FIG. 14A, the beam shaping and illumination system 102 and the projection system 200 may be arranged in a vacuum housing and/or be surrounded by a machine room with corresponding driving apparatuses.

[0133] The DUV lithography apparatus 100B has a DUV light source 106B. By way of example, an ArF excimer laser that emits radiation 108B in the DUV range at 193 nm, for example, can be provided as the DUV light source 106B.

[0134] The beam shaping and illumination system 102 illustrated in FIG. 14B guides the DUV radiation 108B onto a photomask 120. The photomask 120 is formed as a transmissive optical element and may be arranged outside the systems 102, 104. The photomask 120 has a structure which is imaged onto a wafer 124 or the like in a reduced fashion via the projection system 200.

[0135] The projection system 200 has a plurality of lens elements 128 and/or mirrors 130 for imaging the photomask 120 onto the wafer 124. In this case, individual lens elements 128 and/or mirrors 130 of the projection system 104 may be arranged symmetrically in relation to an optical axis 126 of the projection system 200. It should be noted that the number of lens elements 128 and mirrors 130 of the DUV lithography apparatus 100B is not restricted to the number shown. A greater or lesser number of lens elements 128 and/or mirrors 130 can also be provided. Furthermore, the mirrors 130 are generally curved on their front sides for beam shaping.

[0136] An air gap between the last lens element 128 and the wafer 124 can be replaced by a liquid medium 132 having a refractive index>1. The liquid medium 132 may be for example high-purity water. Such a construction is also referred to as immersion lithography and has an increased photolithographic resolution. The medium 132 can also be referred to as an immersion liquid.

[0137] The projection system 200 furthermore has a mirror 210, on the rear side of which an actuator device 220 is arranged, which can be designed as shown in FIG. 2-8, 10 or 13. Without restricting the generality, only one actuator device 220 is shown here, but it goes without saying that a multiplicity of actuator devices 220 can be present, each of which is able to be controlled individually with open-loop and/or closed-loop control. The actuator device 220 comprises an assigned actuator element 222 and an assigned sensor element 224. A drive unit 226 is set up to drive the actuator elements 222 with a drive voltage VS and to apply a measurement alternating voltage VM to the sensor elements 224 in order to generate a respective sensor signal SS.

[0138] Also shown in FIG. 14B is that a predetermined target mechanical stress σ.sub.s is specified from the outside, which is to be achieved by the actuator element 222. The mechanical target stress σ.sub.s is ascertained, for example, by a control computer on the basis of a target deformation of the mirror 210 that is to be achieved. The targeted deformation of the front side of the mirror 210 allows the correction of optical aberrations for increasing the resolution of the lithography process.

[0139] In advantageous embodiments, the actuation is controlled with closed-loop control by the actuator element 222 by virtue of the fact that an actually achieved deformation is detected by the sensor element 224 and the drive voltage VS can therefore be controlled with closed-loop control by evaluating the sensor signal SS. This closed-loop control takes place individually for each actuator device 220, wherein only one actuator device 220 and only one drive voltage VS, one measurement alternating voltage VM and one sensor signal SS are shown for reasons of clarity.

[0140] The projection system 200, or also the beam shaping and illumination system 102, can have further mirrors 210 with an assigned actuator device 220.

[0141] FIG. 15 shows a schematic block diagram of an exemplary embodiment of a method for correcting an aberration in an optical system 200, for example in the optical system 200 of FIG. 1, by deforming the mirror surface 212 (see FIGS. 1-8) of a mirror 210 (see FIG. 1-8 or 14A, 14B) of the optical system 200 in a targeted manner.

[0142] In a first step S1, the at least one actuator element 222 (see FIG. 2-8 or 13) is driven via a drive voltage VS (see FIG. 2-8 or 10-13) in dependence on a specified deformation of the mirror surface 214 (see FIGS. 1-8). As a result, a mechanical stress is produced in the actuator element 222, which stress is transferred to the mirror body 212 (see FIGS. 1-8) of the mirror 210, which leads to a local deformation of the mirror surface 214.

[0143] In a second step S2, a sensor signal SS (see FIG. 2-8 or 13) is output by the at least one sensor element 224 (see FIG. 2-8 or 13). For this purpose, a measuring alternating voltage VM is applied to the sensor element 224, as has already been described above.

[0144] In a third step S3, a deformation of the sensor element 224 is ascertained in dependence on the detected sensor signal SS. An achieved deformation of the mirror surface 214 can be ascertained therefrom.

[0145] In a fourth, optional step S4, the drive voltage VS is controlled with closed-loop control in such a way that the predetermined deformation of the mirror surface 214 is achieved.

[0146] For this purpose, for example, the predetermined deformation is compared with the deformation achieved, which shows whether the drive voltage VS is desirably higher or lower in order to achieve the predetermined deformation.

[0147] Although the present disclosure has been described with reference to exemplary embodiments, it is modifiable in various ways. For example, many of the physical variables that have served to describe the description are interchangeable with other variables. Instead of mechanical stress, it is also possible to refer to force or mechanical strain or deformation. Furthermore, it can be said that the sensor signal is dependent on the dielectric susceptibility, the impedance, the polarization, the capacitance or the like, all of which can be converted into one another as long as the respective material parameters are known.

[0148] For example, the disclosure permits a large number of possible arrangements of a sensor element in relation to an actuator element in an actuator device. The different positions can be advantageous depending on the specific application. In addition, a detection accuracy can be increased by combining different arrangements in one actuator element.

[0149] Furthermore, the closed-loop control circuit for controlling the drive voltage can be implemented or realized in a variety of ways, without the present disclosure being limited in any particular way.

LIST OF REFERENCE SIGNS

[0150] 1 Function curve [0151] 2 Function curve [0152] 3 Function curve [0153] 4 Function curve [0154] 5 Function curve [0155] 100A EUV lithography apparatus [0156] 100B DUV lithography apparatus [0157] 102 Beam shaping and illumination system [0158] 106A EUV light source [0159] 106B DUV light source [0160] 108A EUV radiation [0161] 108B DUV radiation [0162] 110 Mirror [0163] 112 Mirror [0164] 114 Mirror [0165] 116 Mirror [0166] 118 Mirror [0167] 120 Photomask [0168] 122 Mirror [0169] 124 Wafer [0170] 126 Optical axis [0171] 128 Lens element [0172] 130 Mirror [0173] 132 Medium [0174] 200 Optical system [0175] 210 Mirror [0176] 212 Mirror body [0177] 214 Mirror surface [0178] 216 Mirror carrier [0179] 220 Actuator device [0180] 221 Layer [0181] 222 Actuator element [0182] 223 Actuation direction [0183] 224 Sensor element [0184] 226 Drive unit [0185] 230 Ascertainment unit [0186] A1 Anode [0187] A2 Anode [0188] A3 Anode [0189] An Anode [0190] K1 Cathode [0191] K2 Cathode [0192] K3 Cathode [0193] Kn Cathode [0194] L1 Layer [0195] L2 Layer [0196] L3 Layer [0197] Ln Layer [0198] LS Light source [0199] MX Matrix [0200] M1 Mirror [0201] M2 Mirror [0202] M3 Mirror [0203] M4 Mirror [0204] M5 Mirror [0205] S1 Method step [0206] S2 Method step [0207] S3 Method step [0208] S4 Method step [0209] SS Sensor signal [0210] VM Measurement alternating voltage [0211] VS Drive voltage [0212] χ Dielectric susceptibility [0213] σ Mechanical stress [0214] σ.sub.s Mechanical stress