Projection lens of an optical system for microlithography

Abstract

The invention relates to a projection lens of an optical system for microlithography, for imaging a mask situated in an object plane on a first stage onto a wafer or camera sensor situated in an image plane on a second stage. The projection lens comprises a force frame (130, 530), on which a plurality of optical components (140, 541, 542) of the projection lens (100, 500) are arranged, and a measuring structure comprising a first measurement frame (145, 545) assigned to the first stage (155, 555) and a second measurement frame (120, 520) assigned to the second stage (115, 515), the measuring structure being designed to determine the position of the first stage (155, 555) relative to the first measurement frame (145, 545) and to determine the position of the second stage (115, 515) relative to the second measurement frame (120, 520), and wherein the first measurement frame (145, 545) and / or the second measurement frame (120, 520) is mechanically connected to the force frame (130, 530).

Description

[0001]

[0002] Projection lens of an optical system

[0003] for microlithography

[0004] The present application claims the priority of the German patent application DE 10 2025103972.0, filed on 04 February 2025. The content of this DE application is incorporated by reference in the present application text.

[0005] BACKGROUND OF THE INVENTION

[0006] Field of the invention

[0007] The invention relates to a projection lens of an optical system for microlithography.

[0008] Prior art

[0009] Microlithography is used to produce microstructured component parts, such as integrated circuits or LCDs. The microlithography process is performed in what is known as a projection exposure apparatus, which comprises an illumination device and a projection lens. The image of a mask (= reticle) illuminated by means of the illumination device is in this case projected by means of the projection lens onto a substrate (for example a silicon wafer) coated with a lightsensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating on the substrate.Mask inspection systems are used for the inspection of reticles for microlitho-graphic projection exposure apparatuses.

[0010] In projection exposure apparatuses or mask inspection systems designed for EUV (e.g. for wavelengths of e.g. approximately 13 nm or approximately 7 nm), mirrors are used as optical components for the imaging process because of the unavailability of light-transmissive materials. These mirrors may e.g. be arranged on a force frame and be designed to be manipulatable at least in part. There may also be active position control in this context, e.g. in order to compensate for aberrations that occur during the operation of the respective optical system (e.g. as a consequence of thermal influences). Position control is implemented on the basis of a position relative to a sensor frame of the respective mirrors, determined by way of sensors (e.g. distance sensors in the form of optical encoders or interferometer systems). In addition to mirrors whose position is actively controlled, so-called "passive" mirrors may also be provided; the positions thereof cannot be actively controlled, and they are directly mechanically connected to the sensor frame.

[0011] Depending on the structural circumstances present in the specific optical system, it may be expedient or even necessary to provide one or more further measurement frames in addition to the aforementioned sensor frame and / or to subdivide the specified sensor frame into a plurality of units (e.g. each assigned to individual optical components), wherein multiple optical relative measurements can be taken in succession, in particular in the style of a "measurement chain". In this way, it is possible to take account of the fact that in practice a single central sensor frame might not allow for sufficiently accurate measurement of all components of the optical system under certain circumstances; for example, this may be traced back to the available installation space or else to the specific measurement directions of the sensors used.

[0012] The use of further measurement frames present in addition to the aforementioned sensor frame may be necessary in particular for determining the position of the stages present in the object plane and in the image plane, respectively, ofthe projection lens in a microlithographic projection exposure apparatus or else of the projection lens in a mask inspection system (should the invention be applied to a projection lens in a microlithographic projection exposure apparatus, said stages are the reticle stage and the wafer stage). This is true in particular when said sensor frame is implemented not an as external structure — in relation to the projection lens — which surrounds the optical components but rather as an "internal" sensor frame in relation to the projection lens, since said position determination or measurement of the aforementioned stages in the respective planes by way of separate measurement frames is substantially simplified or even only made possible in that case.

[0013] In practice, the realization of the specific measurement chain of sensor frame and further measurement frames (in particular for the aforementioned stages in the object and image planes in the projection lens) represents a demanding challenge, within the scope of which it necessary to consider the existing, possibly strict installation space restrictions on the one hand and the cost factors (e.g. for the provision of the sensors used in the measurement chain and the actuators optionally present for the purpose of feedback control) on the other.

[0014] SUMMARY OF THE INVENTION

[0015] Against the above background, a problem addressed by the present invention is that of providing a projection lens of an optical system for microlithography, said projection lens allowing a reduction in the complexity and the costs in relation to the dynamic architecture, while the optical system still provides sufficient capabilities.

[0016] This problem is solved in accordance with the features of independent Claim 1.

[0017] A projection lens according to the invention of an optical system for microlithography, for imaging a mask situated in an object plane on a first stage onto awafer or camera sensor situated in an image plane on a second stage, comprises:

[0018] a force frame, on which a plurality of optical components of the projection lens are arranged; and

[0019] a measuring structure comprising a first measurement frame assigned to the first stage and a second measurement frame assigned to the second stage, the measuring structure being designed to determine the position of the first stage relative to the first measurement frame and to determine the position of the second stage relative to the second measurement frame;

[0020] wherein the first measurement frame and / or the second measurement frame is mechanically connected to the force frame.

[0021] The measurement frame assigned to the first stage (= reticle stage) in the measuring structure according to the invention may also be referred to as an RSMF (= "Reticle Stage Metrology Frame"). Should the invention be applied to a projection lens in a microlithographic projection exposure apparatus, the second stage is the wafer stage, wherein the second measurement frame may also be referred to as a WSMF (= "Wafer Stage Metrology Frame") in that case. Should the invention be applied to a projection lens in a mask inspection system, the image plane of this projection lens contains not a wafer but a camera sensor for recording an aerial image of the mask to be inspected or of the reticle.

[0022] The present invention in particular contains the concept of mechanically connecting the aforementioned first measurement frame and / or the aforementioned second measurement frame to the force frame, wherein — as described below — this mechanical connection is realized as a purely passive connection or as a connection that can be actuated with a comparatively low bandwidth, with active control of the relative position between the force frame and the sensor frame being dispensed with. As a result, a dynamics and control architecture of comparatively low complexity and with relatively low costs is realized according to the invention, wherein, especially in view of the aforementioned measurementframe, the use of comparatively costly "high performance" actuators is dispensed with.

[0023] In this case, the concept according to the invention of mechanically connecting the respective measurement frame (e.g. the aforementioned RSMF or WSMF) to the force frame (especially by way of a passive mechanical connection) deliberately accepts certain disadvantages or challenges in order to achieve the aforementioned advantages of low complexity and low costs in return:

[0024] For example, in the case of generally unavoidable vibrations of the force frame, passively mechanically connecting the respective measurement frame to the force frame leads in principle to deformations on the respective measurement frame. However, according to the invention these circumstances can be taken into account by virtue of realizing a decoupling of the respective measurement frame at a frequency at which the arising deformation of the measurement frame is minimal or by virtue of the respective deformation being predicted on the basis of a model and then being compensated for accordingly.

[0025] Moreover, a consequence of the inventive passive mechanical connection of the respective measurement frame to the force frame is that active control of the relative position between the force frame and a sensor frame optionally present in embodiments of the invention, which possibly results in greater deflections of the respective measurement frame, is no longer effected. In order to take these circumstances into account, the invention now contains the further principle of providing suitable measures to ensure that the measurement range of the sensor system used is not exceeded. Like in the following, this may be implemented e.g. by a suitable choice of the decoupling frequency between the force frame and the optionally present sensor frame and by damping on the basis of the acting interference. In a further embodiment, the use of a comparatively simple actuator system can also ensure that a measurement frame remains in the respective measurement range by way of a suitable adaptation of the position of the respective measurement frame. However, in this context, attention should be drawn to the fact that the aforementioned simple actuator system does not servefor active position control during the operation of the optical system but is used only for the aforementioned positional adaptation or observation of the measurement range, and so in this respect it is possible to dispense with the use of comparatively complex "high performance" actuators.

[0026] A further challenge in the concept according to the invention emerges from the response path of the respective stage (e.g. the aforementioned RSMF or WSMF), wherein, in this respect, it is imperative to avoid in particular an instability of the control loop as a result of reaction forces arising.

[0027] According to an embodiment, the mechanical connection of the first measurement frame and / or of the second measurement frame to the force frame is a passive connection.

[0028] According to an embodiment, there is a mechanical decoupling (or mechanical decoupling means) present between the first measurement frame and the force frame and / or between the second measurement frame and the force frame.

[0029] According to an embodiment, this mechanical decoupling is a passive mechanical decoupling (or passive mechanical decoupling means).

[0030] According to an embodiment, a decoupling frequency (<w0) of this decoupling is in the range from 10 Hz to 200 Hz.

[0031] According to an embodiment, the mechanical decoupling (or mechanical decoupling means) is an active mechanical decoupling (or active mechanical decoupling means), in which the decoupling frequency (<w0) is actively adjustable.

[0032] According to an embodiment, an actuator system present in the mechanical connection of the first measurement frame and / or of the second measurement frame to the force frame is restricted to a positional adaptation of the measurement frame, and this positional adaptation causes the measurement frame to remainin the respective measurement range and / or a deformation of the respective measurement frame to be reduced.

[0033] According to an embodiment, the measuring structure is designed to determine the position of the optical components and to determine the position of the first measurement frame and of the second measurement frame.

[0034] According to an embodiment, the measuring structure is designed to determine the relative position of the optical components with respect to one another and to determine the position of the first measurement frame and of the second measurement frame.

[0035] According to an embodiment, the measuring structure comprises a sensor frame having a plurality of sensors for determining the position of the optical components and is designed to determine the respective position of the first measurement frame and of the second measurement frame relative to the sensor frame.

[0036] According to an embodiment, the sensor frame is arranged in such a way that the optical components are replaceable independently of the sensors for determining the position of the optical components.

[0037] To this end, said sensor frame may be realized in particular as an "inner" sensor frame in relation to the projection lens in order — unlike for instance in the case of an outer structure in relation to the projection lens, which outer structure surrounds the individual optical components — to allow for the disassembly or assembly of individual optical components or mirrors of the projection lens independently of the sensor frame or the sensors situated thereon. Such a configuration as an "inner" sensor frame in relation to the projection lens has the further advantage that — unlike in the case of an outer structure in relation to the projection lens, which outer structure surrounds the individual optical components — a particularly compact structure of the respective sensor frame is realized, in the case of which moreover comparatively less pronounced deformations occur during operation.However, the invention is not restricted to the presence of a sensor frame but also comprises embodiments in which the inventive mechanical connection of the respective (first and / or second) measurement frame to the load-bearing structure is realized in an architecture without a sensor frame.

[0038] Further configurations of the invention can be gathered from the description and the dependent claims.

[0039] The invention will be explained in detail below on the basis of exemplary embodiments illustrated in the appended figures.

[0040] BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In detail:

[0042] Figure 1 shows a schematic illustration for explaining the dynamics architecture of a projection lens according to the invention in an exemplary embodiment;

[0043] Figure 2 shows a schematic illustration for explaining the thermal architecture of a projection lens according to the invention in an exemplary embodiment;

[0044] Figures 3-4 shows schematic illustrations of exemplary conventional dynamics architectures of a projection lens;

[0045] Figure 5 shows a schematic illustration for explaining the dynamics architecture of a projection lens according to the invention in a further exemplary embodiment; andFigure 6 shows a schematic illustration of a projection exposure apparatus designed for operation in the EUV.

[0046] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0047] Below, a dynamics architecture and a thermal architecture of a projection lens according to the invention are described in respective exemplary embodiments with reference to the schematic illustrations in Fig. 1 and Fig. 2, respectively. Components analogous or functionally identical in comparison with Fig. 1 are denoted in Fig. 2 by reference numerals increased by “100”.

[0048] According to Fig. 1 , a projection lens in a microlithographic projection exposure apparatus in particular comprises a force frame 130 and a measuring structure, with this measuring structure comprising a sensor frame 150 in particular. Furthermore, the measuring structure also comprises a first measurement frame 145 assigned to a first stage 155 (= reticle stage) and a second measurement frame 120 assigned to a second stage 115. In this case, the measuring structure is designed to determine the position of the first stage 155 relative to the first measurement frame 145, to determine the position of the second stage 115 relative to the second measurement frame 120 and to determine the respective position of the first measurement frame 145 and of the second measurement frame 120 relative to the sensor frame 150. In this case, the first stage 155 (= reticle stage) is measured with respect to the sensor frame 150 by way of a measuring chain. In this case, the rigid body position of the first measurement frame (RSMF) 145 is initially measured vis-a-vis the sensor frame 150, and then the rigid body position of the first stage 155 (= reticle stage) is measured vis-a-vis the first measurement frame (RSMF) 145.

[0049] The first measurement frame 145 assigned to the first stage 155 or reticle stage is also referred to below as RSMF (= "Reticle Stage Metrology Frame"). Should the invention be applied to a projection lens in a microlithographic projection exposure apparatus, the second stage 115 is the wafer stage, wherein the secondmeasurement frame may also be referred to as a WSMF (= "Wafer Stage Metrology Frame") in that case. Should the invention be applied to a projection lens in a mask inspection system, the image plane of this projection lens contains not a wafer but a camera sensor for recording an aerial image of the mask to be inspected or of the reticle.

[0050] In the dynamics architecture according to Fig. 1 , the force frame 130 is mechanically decoupled relative to a base frame 110; this may be implemented by way of air mounts, for example. As indicated in Fig. 1 , an illumination device 135 is also mechanically decoupled relative to the base frame 110, e.g. likewise by way of air mounts. A plurality of optical components or mirrors 140 are arranged on the force frame 130, are actuatable by way of actuators and are decoupled by way of a weight compensation device (MGC = "Magnetic Gravity Compensator").

[0051] According to Fig. 1 , the first measurement frame 145 (RSMF = "Reticle Stage Metrology Frame") assigned to the first stage 155 (= reticle stage) is mechanically connected to the force frame 130, with this being a passive connection (without actuation) in the shown exemplary embodiment in particular. In addition to that or in an alternative, the second measurement frame 120 assigned to the second stage 115 may also be mechanically connected (and in particular likewise passively connected) to the force frame 130 in further embodiments. A mechanical decoupling (or mechanical decoupling means) between the first measurement frame (RSMF) 145 and the force frame 130 is denoted by "161". For example, this mechanical decoupling 161 may be configured as a spring. Further possible passive decoupling mechanisms may comprise e.g. flexures, mechanical springs, a magnetic mount or a pneumatic mount (with encapsulation vis-a-vis the vacuum atmosphere).

[0052] In the exemplary embodiment according to Fig. 1 (without the invention being restricted thereto, however), the sensor frame 150 is actively decoupled vis-a-vis the force frame 130 by way of a two-stage decoupling 151 ; however, other decoupling elements may also be used, e.g. a one-stage or three-stage decoupling mechanism.In the exemplary embodiment of Fig. 1 , the second measurement frame 120 (WSMF = Wafer Stage Metrology Frame) assigned to the second stage 115 or wafer stage is decoupled vis-a-vis the base frame 110 by way of a wafer stage intermediate frame (WSIF = Wafer Stage Intermediate Frame) 125 and e.g. by way of air mounts 160. Two stages 115 ("measuring stage and "exposure stage") are measured with respect to the second measurement frame or WSMF 120. The measurement frame or WSMF 120 assigned to the second stage 115 (= wafer stage) may furthermore be measured with respect to the sensor frame 150.

[0053] In simplified terms, a passive decoupling 161 (or passive decoupling means) between the first measurement frame or RSMF 145 and the sensor frame 150 gives rise to a 1-mass oscillator whose behaviour can be described by three system parameters: the overall stiffness kRSMFof the first measurement frame or RSMF 145 vis-a-vis the force frame 130, the overall mass mRSMFof the first measurement frame or RSMF 145 and the dRSMFoverall damping of the decoupling. The decoupling frequency can be determined as >0=

[0054]

[0055] with the aidmRSMF

[0056] of these parameters.

[0057] An optimization between deformation and relative change in position with respect to the force frame 130 may be performed for the suitable choice of the decoupling frequency a>0. The stiffer the connection between the first measurement frame or RSMF 145 and force frame 130, the smaller the relative change in position between the first measurement frame or RSMF 145 and force frame 130, and the higher the forces introduced into the first measurement frame or RSMF 145 (and consequently also the greater the deformation of the RSMF 145). The position of the first measurement frame or RSMF 145 itself is only relevant inasmuch as said position remains within the available measurement range of the measurement technology (e.g. interferometers or encoder systems) used in the first measurement frame or RSMF 145. Stiffness and mass are therefore chosen such that the requirements are fulfilled in respect of a deformationand relative change in position of the first measurement frame or RSMF 145 vis-a-vis the force frame 130 and hence indirectly vis-a-vis the sensor frame 150 that are as small as possible.

[0058] The damping is preferably chosen such that the amplitude overshoot at the resonant frequency lies within the requirements. Moreover, the RSMF 145 and the force frame 130 themselves may also be damped by way of the relative damping between the force frame 130 and the first measurement frame or RSMF 145.

[0059] Moreover, decoupling frequency M0and damping are preferably chosen such that the response path of the control for the first stage 155 (= reticle stage) is robustly stable. Typically, this means that the action path of each frequency is at least 20 dB above the response path.

[0060] The aforementioned decoupling frequency M0should not overlap with the decoupling frequencies of other decoupling stages. Furthermore, this decoupling frequency M0should not match any of the natural frequencies of frame elements or frequencies at which high disturbance amplitudes (e.g. 400 Hz for turbo pumps) are expected. Moreover, the natural frequency M0should not be a frequency at which a significant excitation by stages or other decisive dynamic excitations are to be expected.

[0061] Suitable passive damping mechanisms comprise e.g. tuned mass dampers (TMDs), the use of viscoelastic materials, hydraulic or pneumatic shock absorbers or magnetorheological shock absorbers.

[0062] In further embodiments, the mechanical decoupling 161 may also be an active mechanical decoupling, in which the decoupling frequency (<w0) is actively adjustable. In this context, systems with "active decoupling" refer to all systems comprising an actively controllable actuator system. For example, this allows a certain stiffness to be realized, and hence the decoupling frequency can be set "actively". Moreover, the position of the first measurement frame or RMSF 145 may be actively controlled. However, targeted choice of the decouplingfrequencies and a goal optimization between deformation and relative change in position result in significantly more design freedom in the design of the actuator system. This leads to a balanced system, which is optimized with regard to the "performance / cost ratio". In this case, the usable drives can be distinguished on the basis of the required auxiliary energy: electric / electromagnetic actuators, Lorentz actuators, piezo actuator system, pneumatic actuators, hydraulic actuators. In particular, electric or electromagnetic actuators can be advantageously used for the typical requirements within the projection lens. To generate additional damping, it is possible either to control the actuators or make use of the aforementioned passive damping mechanisms.

[0063] Figure 2 shows a schematic illustration for explaining the thermal architecture of the projection lens according to the invention in an exemplary embodiment. In Fig. 2, "270" is used to denote heat sources or thermal disturbances, and "275" is used to refer to suitable exemplary positions of temperature sensors which are used for thermal control and the compensation of thermal disturbances. Cooling channels through which cooling fluid can flow are denoted by "280". In a manner corresponding to the measurement path there is an error contribution as a result of thermal deformations of the sensor frame 250. Furthermore, it is necessary to take into account the thermal deformation of the interface between the first measurement frame or RSMF 245 and the force frame 230 and also the thermal deformation of the first measurement frame or RSMF 245 itself. In this case, the thermal state at the time of calibration is significant. Temporally fluctuating thermal disturbances after this time automatically result in an imaging aberration, and so the corresponding contribution is preferably kept to a minimum.

[0064] Fig. 3 shows — in comparison with the dynamics architecture according to the invention in Fig. 1 — an exemplary conventional dynamics architecture for a projection lens. Components analogous or substantially functionally identical in comparison with Fig. 1 are denoted here by reference numerals increased by “200”.According to Fig. 3, the first measurement frame or RSMF 345 assigned to the first stage 355 (reticle stage) is mechanically securely connected to the sensor frame 350 and thus follows the movements thereof. Hence, according to Fig. 3, no relative measurement is taken between the sensor frame 350 and the first measurement frame or RSMF 345, and the position of the first stage or reticle stage 355 is determined directly by way of a position measurement in relation to the first measurement frame or RSMF 345. However, according to Fig. 3, said first measurement frame (RSMF) 345 is positioned at a suitable position of the sensor frame 350 for measuring the first stage 355 according to Fig. 3 (specifically at the outermost upper point of this sensor frame 350 in the illustration of Fig. 3), and this in turn is only possible in the use scenario with a correspondingly outer sensor frame 350. By contrast, the dynamics architecture according to the invention according to Fig. 1 can be realized with an "inner" sensor frame (and hence, as described, with a comparatively compact construction of the sensor frame, which moreover allows a disassembly or assembly of individual optical components independently of the sensor frame).

[0065] Fig. 4 shows a further conventional dynamics structure of a projection lens. In contrast to Fig. 3, the sensor frame according to Fig. 4 is indeed embodied as an above-described "inner" sensor frame (to allow for a compact design and the capability of replacing the optical components or mirrors). To measure the first stage or reticle stage 455, this case provides for a two-stage measuring chain, wherein the first measurement frame (RSMF) is attached to the force frame 430 by way of actuators 431 and measured vis-a-vis the sensor frame 450 by way of a position measuring system (interferometer). The first measurement frame or RSMF 445 is position-controlled vis-a-vis the sensor frame 450 with comparatively low bandwidth (e.g. 20 Hz) and using a PID controller, and the first stage or reticle stage 455 is measured with respect to the RSMF 445. However, in comparison with the dynamics architecture according to the invention according to Fig. 1 , the dynamics architecture in Fig. 4 requires a comparatively large installation space for the actuators 431 and the utilized mirror modules.Fig. 5 shows a schematic illustration for explaining the dynamics architecture of a projection lens according to the invention in a further exemplary embodiment, in which the inventive mechanical connection of the respective (first and / or second) measurement frame to the load-bearing structure is realized in an architecture without a sensor frame.

[0066] Components analogous or substantially functionally identical in comparison with Fig. 1 are denoted here by reference numerals increased by “400”.

[0067] According to Fig. 5, the measuring structure between the optical components 541 , 542 and the measurement frame 545, 520 is designed such that the positions of the optical components 541 , 542 and of the first and second measurement frames 545, 520 are ascertained directly and relative to one another. Two optical components 541 , 542 are plotted merely by way of example and only for explanatory purposes in Fig. 5 (without the invention being restricted thereto). In this case, the respective sensor elements and the sensor targets for detecting the relative position of the optical components 541 , 542 with respect to each other are situated directly on the optical components 541 , 542. An additional sensor frame can be omitted in this exemplary embodiment.

[0068] According to Fig. 5, the first measurement frame 545 and the second measurement frame 520 are in each case mechanically connected to the force frame 530, with this being a passive connection (without actuation) in the shown exemplary embodiment in particular. Here, "561 " and "521 " denote mechanical decouplings (or mechanical decoupling means) between the first measurement frame 545 and the force frame 530 and between the second measurement frame 520 and the force frame 530, respectively. In addition to that or in an alternative, at least one of the two measurement frames 545, 520 may be connected to the force frame 530 by way of an actuation (or actuation device) in further embodiments, so that the position of the respective measurement frame 545 or 520 can be actively manipulated.Figure 6 shows a merely schematic illustration of a projection exposure apparatus 1 which is designed for operation in the EUV range and in which the present invention can be implemented by way of example.

[0069] According to Fig. 6, the projection exposure apparatus 1 comprises an illumination device 2 and a projection lens 10. An embodiment of the illumination device 2 of the projection exposure apparatus 1 has, in addition to a light or radiation source 3, an illumination optics unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination device. In this case, the illumination device does not comprise the light source 3.

[0070] In this case, a reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable in particular in a scanning direction by way of a reticle displacement drive 9. By way of elucidation, Fig. 6 shows a Cartesian xyz-coordinate system. The x-direction runs perpendicularly to the plane of the drawing into the latter. The y-direction runs horizontally, and the z-direction runs vertically. The scanning direction runs in the y-direction in Fig. 6. The z-direction runs perpendicularly in relation to the object plane 6.

[0071] The projection lens 10 serves for imaging the object field 5 into an image field 11 in an image plane 12. A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable, in particular in the y-direction, by way of a wafer displacement drive 15. The displacement, firstly, of the reticle 7 by way of the reticle displacement drive 9 and, secondly, of the wafer 13 by way of the wafer displacement drive 15 may be synchronized with each other.

[0072] The radiation source 3 is an EUV radiation source. The radiation source 3 in particular emits EUV radiation, which is also referred to below as used radiation or illumination radiation. In particular, the used radiation has a wavelength in therange of between 5 nm and 30 nm. The radiation source 3 may be, for example, a plasma source, a synchrotron-based radiation source or a free electron laser (FEL). The illumination radiation 16 emanating from the radiation source 3 is focused by a collector 17 and propagates through an intermediate focus in an intermediate focal plane 18 into the illumination optics unit 4. The illumination optics unit 4 comprises a deflection mirror 19 and, arranged downstream thereof in the beam path, a first facet mirror 20 (having schematically indicated facets 21) and a second facet mirror 22 (having schematically indicated facets 23).

[0073] The projection lens 10 comprises a plurality of mirrors Mi (i= 1 , 2, ...), which are consecutively numbered according to their arrangement in the beam path of the projection exposure apparatus 1. In the example illustrated in Fig. 6, the projection lens 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a through-opening for the illumination radiation 16. The projection lens 10 is a doubly obscured optical unit. The projection lens 10 has an image-side numerical aperture that is greater than 0.5 and may also be greater than 0.6 and may be for example 0.7 or 0.75.

[0074] Even though the invention has been described on the basis of specific embodiments, numerous variations and alternative embodiments will be apparent to a person skilled in the art, for example through combination and / or exchange of features of individual embodiments. Accordingly, it goes without saying for a person skilled in the art that such variations and alternative embodiments are also included by the present invention, and the scope of the invention is restricted only within the meaning of the accompanying claims and the equivalents thereof.

Claims

Claims1. Projection lens of an optical system for microlithography, for imaging a mask situated in an object plane on a first stage onto a wafer or camera sensor situated in an image plane on a second stage, having• a force frame (130, 530), on which a plurality of optical components (140, 541 , 542) of the projection lens (100, 500) are arranged; and • a measuring structure comprising a first measurement frame (145, 545) assigned to the first stage (155, 555) and a second measurement frame (120, 520) assigned to the second stage (115, 515), the measuring structure being designed to determine the position of the first stage (155, 555) relative to the first measurement frame (145, 545) and to determine the position of the second stage (115, 515) relative to the second measurement frame (120, 520);• wherein the first measurement frame (145, 545) and / or the second measurement frame (120, 520) is mechanically connected to the force frame (130, 530).

2. Projection lens according to Claim 1 , characterized in that the mechanical connection of the first measurement frame (145, 545) and / or of the second measurement frame (120, 520) to the force frame (130, 530) is a passive connection.

3. Projection lens according to Claim 1 or 2, characterized in that there is a mechanical decoupling (161 , 561, 521) present between the first measurement frame (145, 545) and the force frame (130, 530) and / or between the second measurement frame (120, 520) and the force frame (130, 530).

4. Projection lens according to Claim 3, characterized in that this mechanical decoupling (161 , 561 , 521 ) is a passive mechanical decoupling.

5. Projection lens according to Claim 3 or 4, characterized in that a decouplingfrequency (<w0) of this decoupling is in the range from 10 Hz to 200 Hz.

6. Projection lens according to Claim 3, characterized in that the mechanical decoupling (161 , 561 , 521 ) is an active mechanical decoupling, in which the decoupling frequency (<w0) is actively adjustable.

7. Projection lens according to Claim 1 , characterized in that an actuator system present in the mechanical connection of the first measurement frame (145, 545) and / or of the second measurement frame (120, 520) to the force frame (130, 530) is restricted to a positional adaptation of the respective measurement frame, as a result of which said measurement frame (120, 145, 520, 545) is held in its respective measurement range and / or as a result of which a deformation of said measurement frame (120, 145, 520, 545) is reduced.

8. Projection lens according to any of the preceding claims, characterized in that the measuring structure is designed to determine the position of the optical components (140) and to determine the position of the first measurement frame (145) and of the second measurement frame (120).

9. Projection lens according to any of the preceding claims, characterized in that the measuring structure is designed to determine the relative position of the optical components (541 , 542) with respect to one another and to determine the position of the first measurement frame (545) and of the second measurement frame (520).

10. Projection lens according to any of the preceding claims, characterized in that the measuring structure comprises a sensor frame (150) having a plurality of sensors for determining the position of the optical components (140) and is designed to determine the respective position of the first measurement frame (145) and of the second measurement frame (120) relative to the sensor frame (150).

11. Projection lens according to Claim 10, characterized in that the sensor frame (150) is arranged in such a way that the optical components (140) are replaceable independently of the sensors for determining the position of the optical components (140).

12. Optical system for microlithography, having a projection lens according to any of the preceding claims.

13. Optical system according to Claim 12, characterized in that said optical sys- tern is a microlithographic projection exposure apparatus.

14. Optical system according to Claim 12, characterized in that said optical system is a mask inspection system.

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