WO2018033236A1

WO2018033236A1 - Projection lithography system comprising a measuring device for monitoring lateral image stability

Info

Publication number: WO2018033236A1
Application number: PCT/EP2017/000947
Authority: WO
Inventors: Rolf Freimann; Bernhard Geuppert; Ronald Faassen
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2016-08-18
Filing date: 2017-08-04
Publication date: 2018-02-22
Also published as: DE102016215543A1

Abstract

The invention relates to a projection lithography system comprising a measuring device for monitoring lateral image stability. In an interferometric distance measuring device for measuring an optical path length difference between a reference beam path and a measuring beam path in a volume of gases laden with schlieren inhomogeneities, at least some sections of the diameter of the measuring beam path are at least 0.1 cm. A projection lithography system for microlithography comprises the interferometric distance measuring device.

Description

Projection exposure apparatus with a measuring device for monitoring a lateral imaging stability

The present application claims priority to German Patent Application 10 2016 215 543.1 of 18 August 2016. The entire disclosure of this patent application is incorporated by reference into the present application. Background of the invention

The invention relates to a projection exposure apparatus for microlithography, a method for monitoring a lateral imaging stability of a projection objective of such a projection exposure apparatus, an interferometric distance measuring apparatus and a method for interferometrically measuring a length of a measurement path.

Microlithography projection exposure apparatuses usually comprise a mask transfer stage for holding a mask or "reticle" with mask structures arranged thereon, a wafer transfer stage for holding a substrate in the form of a wafer, and projection optics for imaging the mask structures onto the substrate.

In conventional projection exposure systems, the quality of the image of the mask structures often suffers from lateral shift of the image position. The reason for this can be on the one hand in drift events occurring over a period of several image exposures and on the other hand also in vibrational excitations. If the image position on the wafer fluctuates during the exposure of a field, this can lead to a shift of the latent image in the photoresist. This can also affect overlay errors or so-called overlay errors in the printed structures position

CONFIRMATION COPY In the case of EUV projection exposure systems, for example, a change in a mirror position and / or mirror tilt position in the projection objective often results.

In conventional methods for stabilizing the imaging stability of projection exposure systems, the field position is repeatedly monitored during the exposure of a wafer with suitable alignment or so-called "alignment" sensors and appropriate corrective measures are initiated on the one hand, to reduced wafer throughput numbers, on the other hand, it can not prevent image position errors which occur during an exposure process, ie during the exposure of a wafer, for example due to vibrations.

This problem is often counteracted by a more stable design of a carrier frame, to which the exposure radiation in the projection lens leading optical elements are attached, or by providing a rigid reference frame, with respect to which the optical elements are actively stabilized. However, this leads to increased material costs and greatly increased weight of the projection lens. In a prior art, e.g. DE10 2008 004 762 A1, known approach, an additional measuring beam path in the region or in spatial proximity to the exposure beam path of the projection lens is provided with the lateral imaging stability is monitored during the exposure process. However, this approach requires space in the beam path of the projection lens for the arrangement of the measuring beam path defining elements, which can lead to restrictions in the degrees of freedom in the optical design of the projection lens.

Underlying task

It is an object of the invention to provide an interferometric distance measuring device, a method for interferometrically measuring a length of a measuring device. to provide a projection exposure apparatus with improved lateral imaging stability and a method for monitoring a lateral imaging stability of a projection lens, which solves the aforementioned problems, and in particular for improving the lateral imaging stability no measuring beam path in spatial proximity to an exposure beam path is required as well as no essential Restrictions on wafer throughput must be accepted. In particular, an improvement in the lateral imaging stability during an exposure process should also take place.

Inventive solution

According to one aspect of the invention, there is provided an interferometric distance measuring apparatus for measuring an optical path length difference between a referenced beam path and a measurement beam path in a volume of schlieren-laden gases. The diameter of the measuring beam path is at least partially at least 0.1 cm, in particular at least 0.5 cm, at least 1 cm, at least 3 cm or at least 10 cm. This interferometric distance measuring device may in particular be part of the measuring apparatus of the projection exposure apparatus according to the invention described below.

In particular, the diameter of the measuring beam path is at least 0.1 cm, in particular at least 0.5 cm, at least 1 cm, at least 3, in all sections in which the measuring beam path is not superimposed with the reference beam path cm or at least 10 cm. At least the measuring beam path at least partly runs in the greasy gases. For example, the streaks may be due to low pressure hydrogen gas commonly present in EUV projection exposure equipment. By configuring the measuring beam path with the mentioned diameter can be through the streaks distortions caused in the interferogram by appropriate evaluation of the interferogram, in particular by means of a correlation filter, correct. In this dimensioning, the diameter of the measuring beam path is chosen to be sufficiently large that in the interferogram, in addition to the distorted strip areas caused by the closures, sufficient areas still remain for the evaluation in which the strips are present undistorted. By integrating such a distance measuring device into a projection exposure apparatus for microlithography, an improvement in the lateral imaging stability of the projection exposure apparatus can be achieved.

According to one embodiment, the interferometric distance measuring device is configured to generate a multi-strip interference pattern by superposing a measurement radiation guided in the measurement beam path with a reference radiation guided in the reference beam path. Furthermore, the interferometric distance measuring device comprises an evaluation unit, which is configured to correct local disturbances in the multi-strip interference pattern by means of a correlation filter. Thus, localized perturbations in the multi-stripe interference pattern caused by streaking can be corrected and the corrected multi-stripe interference pattern can be evaluated to determine the path length difference.

According to a further embodiment, the interferometric distance measuring device comprises a retroreflector for back reflection of a measuring radiation passing through the measuring beam path, the normal to the retroreflector relative to the propagation direction of the measuring radiation by at least 1 mrad, in particular by at least 5 mrad, by at least 10 mrad at least 20 mrad or at least 30 mrad, is tilted.

According to a further embodiment, the measuring beam path has at least two sections which are tilted relative to one another. The tilting of the two sections is in particular a tilt by at least 10 ° or at least 20 °, for example by 90 ° to understand. Everyone, only one or both of them Nand tilted portions of the measuring beam path may be sections in a region of the measuring beam path, which is superimposed by the reference beam path. Thus, one or both of the mutually tilted sections of the measurement beam path may be part of a so-called measurement path in which the reference radiation does not run. Such a measuring beam path with mutually tilted sections, also referred to as an "angled measuring beam path" in this text, generally has a relatively long measuring beam path in which local disturbances in the interference pattern caused by streaks occur particularly frequently Distance measuring device can be achieved with such an angled measuring beam path good measurement results.

According to a further embodiment, the measurement beam path comprises a measurement path in which the measurement beam path is not superimposed by the reference beam path, the measurement path having a length of at least 0.5 m, in particular at least 1 m or at least 2 m. With such a long measuring path, local disturbances in the interference pattern caused by streaks occur particularly frequently. Due to the inventive design of the interferometric distance measuring device, good measurement results can be achieved even with such an angled measuring beam path.

According to a further embodiment, the interferometric distance measuring device comprises a pressure gauge for measuring a pressure in the region of the measuring beam path and the interferometric distance measuring device is configured to take into account the pressure measured value in determining the optical path length difference.

Furthermore, a projection exposure apparatus for the microlithography with a projection objective for imaging mask structures onto a substrate by means of exposure radiation and an interferometric distance measuring apparatus in one of the embodiments described above are provided according to the invention. In particular, the interferometric distance Measuring device of monitoring a lateral imaging stability of the projection lens.

According to an embodiment of the projection exposure apparatus, the projection objective comprises optical elements for guiding the exposure radiation, a support frame to which the optical elements are fastened by means of actuators, a sensor frame, which is mounted on the support frame by means of a vibration damper, position sensors which are configured to operate the projection exposure system to measure the respective position of the optical elements with respect to the sensor frame and to control the actuators to correct measured changes in position. The distance measuring device is configured to determine during the operation of the projection exposure apparatus at least one deformation parameter characterizing a deformation of the sensor frame.

Furthermore, according to the invention, a method is provided for the interferometric measurement of a length of a measuring section, which passes through a volume of gases laden with striae. The method comprises the steps of irradiating the measuring path with a measuring beam whose diameter is at least in sections at least 0.1 cm, and interferometrically measuring a path length difference between a reference beam path and a measuring beam path comprising the measuring path.

According to one embodiment of the method according to the invention, the interferometric measurement of the path length difference comprises evaluating a multi-strip interference pattern generated by superimposing a measuring radiation guided in the measurement beam path with a reference radiation guided in the reference beam path and evaluating the multi-strip interference pattern by means of a correlation filter in the multi-strip interference pattern. The features specified with respect to the above-mentioned embodiments, exemplary embodiments or design variants, etc. of the distance measuring device according to the invention or the projection exposure apparatus according to the invention can be correspondingly transferred to the method according to the invention. These and other features of the embodiments according to the invention are explained in the description of the figures and the claims. The individual features can be realized either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments which are independently protectable and their protection is possibly claimed only during or after pending the application.

According to a further aspect of the invention, a projection exposure apparatus for microlithography is provided with a projection objective for imaging mask structures onto a substrate by means of exposure radiation. The projection objective comprises optical elements for guiding the exposure radiation, a support frame, to which the optical elements are fastened by means of actuators, a sensor frame, which is mounted on the support frame by means of a vibration damper, position sensors, which are configured, in operation Projection exposure system to measure the respective position of the optical elements with respect to the sensor frame and to control the actuators to correct measured changes in position, and a measuring device for monitoring a lateral imaging stability of the projection lens, which is configured during operation of the projection exposure system at least one to determine a deformation parameter characterizing deformation of the sensor frame.

According to one embodiment of the projection exposure apparatus according to the further aspect, the measuring device comprises an activity sensor for measuring an activity parameter of the vibration damper and an evaluation device for determining the deformation parameter from the activity parameter. According to a further embodiment, the activity sensor comprises a distance sensor for measuring a mechanical deformation of the vibration damper. The distance sensor may in particular be configured as an interferometric distance measuring device in one of the embodiments described above.

According to a further embodiment, the measuring device comprises an acceleration sensor for measuring an acceleration of the sensor frame.

According to a further aspect of the invention, there is provided a microlithography projection exposure apparatus which has a projection objective for imaging mask structures onto a substrate by means of exposure radiation. The projection objective comprises optical elements for guiding the exposure radiation, a stabilization frame, which serves to stabilize an arrangement of the optical elements relative to one another during operation of the projection exposure apparatus, and a measuring device for monitoring a lateral imaging stability of the projection objective. The measuring device is configured to determine during the operation of the projection exposure apparatus at least one deformation parameter characterizing a deformation of the stabilization frame.

In this connection, the lateral imaging stability of the projection objective indicates to what extent the lateral position of the image of mask structures imaged into the substrate plane by means of the projection optics remains stable over time in the exposure mode of the projection exposure apparatus. The lateral position of the image is understood to mean its position in the substrate plane. The said stabilization frame may be formed by a support frame to which the optical elements are attached, or by a sensor frame. Such a sensor frame is mounted on the carrier frame by means of one or more vibration dampers and comprises sensors which are configured to measure the respective position of the optical elements in relation to the sensor frame during operation of the projection exposure apparatus and to trigger the acceleration. to control actuators to correct measured changes in position. The deformation parameter can specify, for example, a distance between two reference points of the stabilization frame or also a deformation shape of the stabilization frame.

In particular, the deformation parameter is determined several times during the operation of the projection exposure apparatus. According to an embodiment variant, the determination of the deformation parameter takes place in real time or at a repetition rate which lies in the range of a sampling rate for controlling the projection objective. The determination according to the invention of the deformation parameter makes it possible to effect a correction of a lateral aberration resulting from the change of the deformation parameter in the case of a deviation of the latter from a desired value or a previously determined value of the deformation parameter. In this way, the lateral imaging stability of the projection lens can be improved during an exposure process without restrictions in the wafer throughput without a measurement beam path arranged in spatial proximity to the exposure beam path.

According to one embodiment, the projection exposure apparatus is an EUV projection exposure apparatus, i. the operating wavelength of the projection exposure apparatus is in the extreme ultraviolet radiation wavelength range.

According to a further embodiment, the projection exposure apparatus further comprises a correction device which is configured to generate at least one correction signal for correcting a lateral aberration of the projection lens resulting from the change of the deformation parameter by manipulation of at least one element arranged in the beam path of the exposure radiation.

According to a further embodiment, the correction device is configured to change the deformation parameter resulting therefrom To determine change in the position of at least one of the optical elements and to effect a correction of the situation. A position of an optical element is its position in at least one of three orthogonal spatial directions and / or its orientation with respect to at least one of three orthogonal tilt axes, ie its positioning with respect to at least one of the six rigid body degrees of freedom, in particular with respect to all six rigid body degrees of freedom , to understand.

According to a further embodiment, the correction device is configured to determine a resulting lateral aberration of the projection lens when the deformation parameter is changed and to correct the lateral aberration by changing the position of an element arranged in the beam path of the exposure radiation. According to a further embodiment, the measuring device comprises a distance measuring device, which is configured to measure the at least one deformation parameter in the form of a distance between two reference points of the stabilization frame. In particular, the measuring device comprises at least two or more distance measuring devices, each of which is configured to measure a distance between respective reference points of the stabilizing frame. Thus, the distances of several reference points to each other can be measured, whereby the underlying deformation of the frame can be determined in detail. According to a further embodiment, the distance measuring device comprises at least one interferometer. In particular, the interferometer is configured to generate a multi-strip interference pattern. In such an interferometer, a measurement radiation is split into a test beam and a reference beam are tilted toward one another in such a way that their superposition in a detection plane of the interferometer generates a multi-strip interference pattern. Under a multi-stripe interference pattern, this text is to be understood as an interference pattern which is at least one full period apart. includes alternating streaks of constructive and destructive interference. By a full period is meant that the phase difference between the interfering waves along the multi-strip interference pattern occupies all values between 0 and 2TT. In other words, a multi-strip interference pattern is an interference pattern having at least two stripes, which stripes may be bright stripes (constructive interference) or dark stripes (destructive interference). In particular, a multi-stripe interference pattern may comprise at least two, at least five, at least ten, at least fifty or at least a hundred full periods of alternating streaks of constructive and destructive interference. Such an interference pattern is often referred to as a multi-strip interference pattern.

According to a further embodiment, the distance measuring device comprises an interferometric distance measuring device for measuring an optical path length difference between a reference beam path and a measuring beam path in a volume of streaked gases, wherein a diameter of the measuring beam path is at least 0.1 cm, in particular at least 0.5 cm. In particular, when measuring an optical path length difference, the measurement of a relative path length difference, i. to understand a slight deviation of the path length difference from the path length difference underlying a previous measurement.

According to a further embodiment, the interferometric distance measuring device comprises a retroreflector for the back reflection of a measuring radiation passing through the measuring beam path, wherein the normal to the retroreflector is tilted by at least 0.1 mrad with respect to the propagation direction of the measuring radiation.

According to a further embodiment, the projection lens comprises a support frame to which the optical elements are attached, the stabilization frame comprising the support frame. In particular, the stabilization frame is the support frame. The attachment to the support frame can be rigid or also actuatable, ie by means of actuators, with which the optical elements are variable in their position, take place. According to an embodiment variant, in the measuring device, from the measured distances between the two reference points of the stabilization frame, in particular the carrier frame, on the basis of finite element modeling (also referred to in this text as "FE modeling") of the stabilization frame In this case, the measuring device can use a transformation matrix determined by means of the FE model From the calculation of the deformation of the stabilization frame it is possible to deduce a resulting change in the arrangement of the optical elements.

According to a further embodiment, the projection objective comprises a support frame to which the optical elements are fastened by means of actuators, a sensor frame, which is mounted on the support frame by means of a vibration damper, and position sensors which are configured to control the respective position of the optical during operation of the projection exposure apparatus Measure elements related to the sensor frame and control the actuators to correct measured position changes. According to this embodiment, the stabilization frame comprises the sensor frame, in particular the stabilization frame is the sensor frame. Vibration dampers, also insulators or shock absorbers, may include deformation elements, such as springs, or pendulum systems, etc. include. According to one embodiment, the measuring device comprises an activity sensor for measuring an activity parameter of the vibration damper and an evaluation device for determining the deformation parameter from the activity parameter. From the measured activity parameter, a deformation shape of the sensor frame can be determined as a deformation parameter. In particular, an acceleration of the sensor frame is first calculated from the measured activity parameter and from this the resulting deformation shape is calculated. This can be done by means of a finite element model. According to a further embodiment, the activity sensor comprises a distance sensor for measuring a mechanical deformation of the vibration damper. In particular, the distance sensor measures an expansion or compression of the vibration damper during the operation of the projection exposure apparatus. In this case, the vibration damper may be formed as a spring.

According to a further embodiment, the measuring device comprises an acceleration sensor for measuring an acceleration of the sensor frame. By means of the acceleration measured during operation of the projection exposure apparatus, a deformation form of the sensor frame can be determined as a deformation parameter. In particular, the resulting deformation shape is calculated from the measured acceleration of the sensor frame. This can be done by means of a finite element model.

According to one embodiment, the measuring device is configured to determine the at least one deformation parameter for a deformation of the stabilization frame generated by oscillations in the range between 0.1 Hz and 10 Hz.

According to a further embodiment, the measuring device has a measuring rate of more than ten measurements, in particular more than twenty measurements, per mask exposure. In particular, the time required for the measurement of the deformation parameter and determination of the resulting deformation of the stabilization frame is less than 10 ms, in particular less than 5 ms.

Furthermore, a method for monitoring a lateral imaging stability of a projection objective of a projection exposure apparatus for microlithography during operation of the projection exposure apparatus is provided according to the invention. In the operation of the projection exposure apparatus, mask structures are exposed by means of an exposure radiation which is emitted by the projection is objectively arranged and guided to each other by means of a stabilizing frame stabilized optical elements, imaged onto a substrate. According to the method according to the invention, at least one deformation parameter characterizing a deformation of the stabilization frame is determined.

The features specified with regard to the above-mentioned embodiments, exemplary embodiments or design variants, etc. of the projection exposure apparatus according to the invention can be correspondingly transferred to the method according to the invention. These and other features of the embodiments according to the invention are explained in the description of the figures and the claims. The individual features can be realized either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments which are independently protectable and their protection is possibly claimed only during or after pending the application.

Brief description of the drawings

The above and other advantageous features of the invention will become apparent in the following detailed description of exemplary embodiments according to the invention with reference to the accompanying schematic

Drawings illustrated. It shows:

1 is a schematic sectional view of an embodiment of a projection exposure apparatus for microlithography with a support frame and a distance measuring device for determining a distance value between two reference points of the support frame, 2 shows an exemplary embodiment of the distance measuring device according to FIG. 1 in the form of a multi-strip interferometer with a displaceable reflector, FIG. 3 shows a retroreflector which can be used instead of the reflector according to FIG. 2 in the multi-strip interferometer and a resulting multi-strip interferogram, FIG.

4 shows a sectional view of a further embodiment of a projection exposure apparatus for IV microlithography with two distance measuring devices with a function according to FIG. 1,

5 is a sectional view of a projection lens of another embodiment of a projection exposure system for IVlikrolithographie for combination with distance measuring devices with a function of FIG. 1,

6 is a sectional view of a further embodiment of a projection exposure apparatus for IVlikrolithographie with a present in undeformiertem condition sensor frame and a measuring device for determining a deformation shape of the sensor frame,

7 shows a sectional view of the projection exposure apparatus according to FIG. 6, in which the sensor frame is in a deformed state, FIG.

8 shows a sectional view of a further embodiment of a projection exposure apparatus for IV microlithography with a sensor frame present in an undeformed state and a measuring device for determining a deformation shape of the sensor frame. Detailed description of inventive embodiments

In the embodiments or embodiments or design variants described below, functionally or structurally similar elements are provided as far as possible with the same or similar reference numerals. Therefore, for the understanding of the features of the individual elements of a particular embodiment, reference should be made to the description of other embodiments or the general description of the invention.

To facilitate the description, a Cartesian xyz coordinate system is indicated in the drawing, from which the respective positional relationship of the components shown in the figures results. In Fig. 1, the x direction is perpendicular to the plane of the drawing, the z direction is to the right and the y direction is upward.

1 illustrates a first embodiment according to the invention of a projection exposure apparatus 10 for microlithography. The projection exposure system 10 comprises a frame 12 having a base frame 31 and a support frame 32. Attached to the base frame 31 are a mask displacement platform 14, the support frame 32 and a wafer transfer stage 22. On the support frame 32 optical elements of a projection lens 30 of the projection exposure apparatus 10 are attached. In the projection objective 30 according to FIG. 1, two such optical elements M1 and M2 are shown in the form of mirrors for illustrative purposes, and in other embodiments, more than two optical elements may also be provided. The support frame 32 thus serves to stabilize the arrangement of the optical elements M1 and M2 and is therefore also referred to as a stabilization frame. In the embodiment shown in FIG. 1, the support frame 32 comprises two vertically arranged side elements 32a and 32c and two horizontally arranged transverse elements 32b and 32d, the connection points of the elements serving as reference points A, B, C and D. The projection objective 30 is used to image mask structures arranged on a mask 16 onto a substrate in the form of a wafer 24. For this purpose, an exposure radiation 34 is irradiated onto the mask 16 by a lighting device (not shown in the drawing), after interacting with the mask 16 it passes through the projection objective 30 by reflection on the optical elements M1 and M2 and finally strikes the wafer 24. The wavelength of the exposure radiation 32 in the present case lies in the extreme ultraviolet wavelength range (EUV), for example at about 13.5 nm or 6.8 nm, but in other embodiments of the projection exposure apparatus 10 can also be in the UV wavelength range, for example at 248 nm or 193 nm. The optical elements M1 and M2 are configured as mirrors in the case shown. Depending on the wavelength of the exposure radiation 34, the optical elements of the projection lens 30 may be embodied as lenses and / or as mirrors.

The mask 16 and the wafer 24 are each arranged displaceably transversely to the beam direction of the exposure radiation 34 on a slide carriage 18 or 26 relative to the respective base 20 or 28 of the mask shift stage 14 or the wafer shift platform 22. During the exposure process, mask 16 and wafer 24 are displaced in opposition to each other, whereby a scanning movement is performed.

The mass reciprocating masses of the mask transfer stage 14 or the wafer transfer stage 22 are often not fully balanced and can therefore exert vibration excitations on the frame 12. Significant portions of these vibration excitations will be referred to as vibrational excitation 40 hereinafter. Furthermore, significant levels of ground vibration can cause such vibration excitation 40. The vibration excitation 40 is typically in the range between 0.1 Hz and 10 Hz, in particular between 0.1 Hz and 3 Hz, and may lead to a deformation of the support frame 32, which occurs at the frequency of the vibration excitation 40. In this case, the support frame 32 changes with the frequency the vibration excitation 40 between an undeformed shape and a deformed shape back and forth.

Such a deformed shape may be characterized, for example, in that the upper cross member 32b of the support frame 32 is bent upwardly at the reference point C (see C) while the adjoining side member 32c is simultaneously bent slightly to the left. Due to the attachment of the optical element M1 in the upper portion of the side member 32c, this deformation shape leads to a tilting 44 of the optical element M1, which causes the beam path of the exposure radiation 34 is tilted at the optical element M1, whereby the image of the mask structures a shift in the level of the wafer 24, ie undergoes a lateral displacement with respect to the wafer surface. In other words, a so-called line-of-sight error or a lateral aberration 35 arises, so that the lateral imaging stability of the projection objective 30 is impaired.

The projection exposure apparatus according to FIG. 1 is configured to correct a real-time correction of the lateral aberration occurring periodically on account of the vibration excitation 40 and thus to greatly improve the lateral imaging stability. For this purpose, the projection exposure apparatus 10 comprises a measuring device 46 for monitoring the lateral imaging stability of the projection objective 30. During operation of the projection exposure apparatus 10, the measuring device 46 determines at short intervals, at least one deformation parameter characterizing the deformation of the support frame 32, in this case in the form of a distance value 50 the reference points C and D. For determining the distance value 50, the measuring device 46 comprises a distance measuring device 48, for example in the form of an interferometer in one of the embodiments illustrated in Figures 2 and 3 and described in more detail below.

The measuring device 46 further comprises an evaluation device 52. Therein, the distance value 50 determined by the distance measuring device 48 becomes 50 determined by means of a simulation model, in particular on the basis of a finite element modeling (FE modeling), the support frame 32, a resulting deformation of the support frame 32 in the form of a deformation shape 54. The evaluation device 52 can use, for example, a transformation matrix determined by means of an FE model of the support frame 32 to determine the deformation of the support frame 32. The deformation form 54 can also be regarded as a deformation parameter determined by the measuring device 46. According to further embodiments, in addition to the distance value 50 between the reference points C and D, further distance values between other reference points, such as the distance value between the reference points A and B or between the reference points B and C, may be included in the simulation calculation.

The deformation form 54 determined by the evaluation device 52 is transferred to a correction device 56. The correction device 56 generates therefrom correction signals 58. This can be a correction signal 58-2 for controlling an actuator 36 of one or more optical elements, in the case of the first optical element M1 shown in FIG. 1, a correction signal 58-1 for controlling the mask shift stage 14 and / or a correction signal 58-3 for controlling the wafer shift stage 22 act. To generate the correction signal 58-2 to the actuator 36, the control device 56 calculates from the transmitted deformation form 54 a resulting change in the position of one or more optical elements. In the case illustrated in FIG. 1, as already mentioned above, the deformation form 54 of the support frame 32 is characterized in that upper transverse element 32b is bent upwards at the reference point C and the adjacent side element 32c is slightly bent to the left. From this, the correction device 56 calculates the resulting tilt 44 of the optical element M1 and, as a correction signal 58-2, gives an instruction to the actuator 36 to carry out a corresponding correction of this tilting. This is done by executing one of the tilting 44 opposite correction movement 60 of the actuator 36 to a suitable tilting axis 38. In other words, the correction signal 58-2 serves da- to immediately correct a change in position of one or more optical elements of the projection lens 30 caused by the frame deformation. Alternatively, the control device 56 may also be configured to obtain the resulting lateral aberration 35 from the transmitted deformation shape 54 by calculating the resulting positional changes of the optical elements M1 and / or M2 and the resulting change in the beam path of the exposure radiation 34 in the projection objective 30 determine. Furthermore, the correction device 56 sends the correction signal 58-1 and / or 58-3 to the mask shift stage 14 or the wafer shift stage 22 for carrying out a correction movement 62 or 64 serving to correct the lateral aberration 35 in the form of a lateral displacement of the mask 16 or the wafer 24. The correction signal 58-2 can also be configured to only partially correct the positional change of the optical element M1 and / or M2 and additionally be combined with the correction signals 58-1 and / or 58-3 according to an embodiment variant.

FIG. 2 shows an embodiment of the distance measuring device 48 according to FIG. 1. This is configured in the form of a Fizeau interferometer and comprises a measuring radiation beam-in module 89 for providing measuring radiation 66 in the form of an expanded measuring beam 98.

The measuring radiation irradiation module 89 comprises a measuring radiation source 93 as well as a telescope with two focusing optics 95 and 97 and an aperture 96. The measuring radiation source 93 generates the measuring radiation 66, for example in the form of a laser beam. The laser beam is focused by the focusing optics 95 on the aperture 96 such that a divergent beam of coherent light emanates from the aperture. The wavefront of the divergent beam is substantially spherical. The divergent beam is collimated by the focusing optics 97, whereby the measuring beam 98, widened in comparison to the beam generated by the measuring radiation source 93, is generated with a substantially planar wavefront. For the Measuring radiation 66 are wavelengths in the visible or near infrared range in question. For example, helium neon lasers, laser diodes, solid-state lasers and LEDs can be used as measuring light sources. The measuring radiation 66 is directed by a beam splitter 68 onto a splitting element 70 in the form of a fizzle element with a fizzle surface 71.

A portion of the incoming measuring radiation 66 is reflected as a reference beam 74 on the Fizeaufläche 71 of the splitting element 70. The radiation of the measuring radiation 66 passing through the splitting element 70 runs along an optical axis 69 of the distance measuring device 48 and, as measuring beam 72, strikes a displaceable reflector 80 in the form of a plane mirror. Since the measuring beam 72 has a planar wavefront, it passes back into the reflector 80 after reflection and then passes through the splitting element 70 and the beam splitter 68. The measuring beam 72 and the reference beam 74 are then by means of a camera lens 76 to a detector 78 for generating focused on an interference pattern. The beam path of the measuring beam 72 extending from the fizzle surface 71 via the reflector 80 as far as the detector 78 is referred to as a measuring beam path. The beam path of the reference beam 74 extending from the fizzle surface 71 to the detector 78 is referred to as the reference beam path.

The arrangement of the measuring radiation beam-in module 89, the beam splitter 68, the camera objective 76 and the detector 78 is also referred to as measuring head 67.

The cleavage element 70 is arranged tilted. The tilting is such that the fizzle surface of the splitting element 70 is tilted with respect to the optical axis 44 by a tilt angle β, which is chosen such that the interference pattern generated on the detector 78 is a multi-strip interference pattern 84, also known as a multi-strip interference pattern. is. In general, a multi-stripe interference pattern in this text is to be understood as an interference pattern which is at least one full period apart. includes alternating streaks of constructive and destructive interference. By a full period is meant that the phase difference between the interfering waves along the multi-strip interference pattern occupies all values between 0 and 2π. In other words, a multi-strip interference pattern is an interference pattern having at least two stripes, which stripes may be bright stripes (constructive interference) or dark stripes (destructive interference). According to advantageous embodiments, at least five, in particular more than 30, light and dark stripes can each be contained in the multi-strip interference pattern 84 generated on the detector 78. According to one embodiment, for the tilt angle β: β> 100 · A / DR.

Here λ is the wavelength of the measuring radiation 66 and DR is the beam diameter of the reference beam 74 at the location of the splitting element 70. According to a numerical example, λ = 633 nm, DR = 5 mm and thus β> 13 mrad.

The path length difference between the beam path of the reference beam 74, which extends from the Fizeaufläche 71 to the detector 78, and the beam path of the measuring beam 72 which extends from the Fizeaufläche 71 to the reflector 80 and then back to the detector 78 corresponds to that The measuring head 67 of the measuring device 48 further comprises an evaluation unit 94. In this, by evaluating the interference pattern 84, the length of the measuring section 75, and in particular a change of the measuring section 75, with high Accuracy determined. The length determined in this way is the distance value 50 mentioned above with reference to FIG. 1, for example between the reference points C and D. The distance measuring device 48 shown in FIG. 2 is configured to operate in greases having greases 82, such as occur due to low pressure hydrogen gas frequently contained in EUV projection exposure equipment. Such streaks cause local perturbations 85 in the multi-fringe interference pattern 84 in the form of fringe distortions. According to the embodiment of the invention shown in FIG. 2, the diameter D of the beam path of the measuring beam 72, ie of the measuring beam path, has a value of at least 0, at least in the region of the measuring path 75 in which the measuring beam path is not superimposed with the beam path of the reference beam 74. 1 cm, in particular at least 0.5 cm, at least 1 cm, at least 3 cm or at least 10 cm on. In order to adjust the diameter D of the beam path accordingly, the focusing optics 95 and 97 of the measuring radiation irradiation module 89 are set appropriately. According to a further embodiment variant, the diameter of the beam path of the measuring beam 72 over its entire length is at least 0.1 cm, in particular at least 0.5 cm, at least 1 cm, at least 3 cm or at least 10 cm.

This value of the diameter is selected to be sufficiently large that, in addition to the distorted stripe regions in the form of the local perturbations 85 caused by the streaks, sufficient regions still remain for the evaluation in which the stripes are undistorted. For this purpose, in the evaluation unit 94, the multi-strip interference pattern 84 is corrected with the local interferences 85 by means of a correlation filter, and the corrected multi-strip interference pattern 86 is evaluated for determining the length of the measuring section 75.

Furthermore, the measuring device 48 may include a pressure measuring device 91 for measuring the gas pressure in the region of the measuring beam path 72. In the embodiment shown, the pressure measuring device 91 for measuring the gas pressure is arranged in the region of the measuring section 75. The pressure measurement value is taken into account by the evaluation unit when determining the length of the measurement path 75, which improves its accuracy. According to a further embodiment of the distance measuring device 48 according to FIG. 2, instead of the reflector 80 embodied as a plane mirror, a retro-reflector 88 shown in FIG. 3 can be used for retro-reflection of the measuring beam 72. The retroreflector 88 may be constructed of a plane mirror 90 and a littrow grid 92 deposited thereon. The retroreflector 88 is tilted such that the normal on the plane mirror 90 of the retort reflector pivots with respect to the direction of the measuring beam 72 by at least 1 mrad, in particular by at least 5 mrad, at least 10 mrad, at least 20 mrad or at least 30 mrad is. In this configuration, not only, as in the embodiment of FIG. 2, a displacement of the reflector 80 or 88 parallel to the measuring beam 71, but also a displacement of the reflector 88 transverse to the measuring beam 71, to a phase shift between the measuring beam 72 and the reference beam 74 , which results in the interference pattern 84 shifting in position on the detector 78. Thus, in this embodiment, positional changes between the reference points C and D of the support frame 32 can be determined in at least two mutually orthogonal dimension directions.

In particular, in one embodiment of the distance measuring device 48, a reflector unit may be provided in which, in addition to the reflector 80 in the form of a plane mirror according to FIG. 2, the retroreflector 88 according to FIG. 3 is also arranged. By evaluating the position of the interference pattern generated by the reflector 80 on the detector 78, the position of the reflector unit in the measuring beam direction, i. in the x-direction according to FIG. 2, and by evaluating the position of the interference pattern generated by the retroreflector 88, the position of the reflector unit transversely to the measuring beam direction, i. in the z-direction of FIG. 2, are determined.

FIG. 4 shows a projection exposure apparatus 10 in an embodiment which is already known in its basic structure from FIG. 1 of US Pat. No. 7,423,724 B2 and the associated description, which is incorporated by reference into the disclosure of the present text. One of the lighting The incoming exposure radiation 34-1 serving for the mask 16 is, after reflection on the mask 16, directed onto a wafer 24 as exposure radiation 34-2 via the optical elements M1 to M6 of a projection objective 30 in the form of mirrors. Analogously to the embodiment according to FIG. 1, the mask 16 is held by a mask shift stage 14 and the wafer 24 by a wafer shift stage 22. Compared with the embodiment according to FIG. 1, the projection objective 30 according to FIG. 4 comprises not only one, but two support frames, namely a first support frame 32-1, to which the optical elements M1 to M4 are fastened, and a second support frame 32-2 to which the optical elements M5 and M6 are attached.

Depending on the design of a projection lens, the lateral image position can be particularly sensitive to the displacement of certain mirrors. This can e.g. Be mirror, which are arranged in the rear part of the exposure beam path in the projection lens. In the embodiment according to FIG. 4, the stability of the mirrors M5 and M6 is considered to be particularly critical with respect to lateral image position errors. Therefore, the second support frame 32-2 holding the two mirrors M5 and M6 is monitored for possible deformation during an exposure operation. For this purpose, distance measuring devices 48-1 and 48-2 of the type described above for measuring distance values in the vertical direction, which in this case is arranged parallel to the optical axis of the projection objective 30, are provided. A first distance measuring device 48-1 serves to measure a distance value between reference points A and B arranged on the left side of the second carrier frame 32-2. The second distance measuring device 48-2 on the other hand serves to measure a distance value between on the right side of the second carrier frame 32-2 arranged reference points C and D. The evaluation of Abstandsmesswer- te and use to stabilize the lateral imaging behavior is analogous to the operation described in connection with FIG.

FIG. 5 shows that already shown in FIG. 2 of US Pat. No. 8,027,022 B2 and the associated description, which are incorporated by reference in the disclosure of the present text. Tes recorded, known beam path of a projection lens 30 of another embodiment of a projection exposure system. In this, the exposure radiation 34-1 irradiated by a lighting module onto a mask 16, after reflection on the mask as exposure radiation 34-2, is first applied to a grazing incidence so-called G mirror 90 (this can also include the term "grazing incidence mirror This is followed in the beam path of the projection objective 30 by the further optical elements M1 to M6, which are mirrors operated at conventional angles of incidence In particular, distance values between reference points of the carrier frame are monitored, which reflect the stability of the optical elements M5 and M6 Stabilization of the lateral imaging behavior is analogous to the operation described in connection with FIG.

FIGS. 6 and 7 illustrate another embodiment of a projection exposure apparatus 10 for microlithography with a projection objective 30, which is mounted next to a support frame 32 on which optical elements M1 and M2 are mounted in the form of mirrors by means of actuators 36-1 and 36-2 , a stabilization frame in the form of a sensor frame 102 has. FIG. 6 shows the projection exposure apparatus 10 in the idle state, while FIG. 7 shows the projection exposure apparatus 10 in a state in which vibration excitations are exerted on a frame frame 12 comprising the support frame 32. Significant portions of these vibration excitations will be referred to as vibrational excitation 40 hereinafter. This vibration excitation 40 is typically in the range between 0.1 Hz and 10 Hz, in particular between 0.1 Hz and 3 Hz, and may by ground vibrations or by the reciprocating during the scanning masses of a mask shift stage 14 and a Wafer shift platform 22 are generated. As shown in FIG. In this case, the vibration excitation 40 results in deformation of the sensor frame 102. At this time, the sensor frame 102 reciprocates at the frequency of vibration excitation between the undeformed shape shown in FIG. 6 and the deformed shape shown in FIG.

The projection objective 30 is used to image mask structures arranged on a mask 16 onto a substrate in the form of a wafer 24. For this purpose, an exposure radiation 34 is irradiated onto the mask 16 by a lighting device which is not shown in the drawing. After interacting with the mask 16, the projection objective 30 passes through Reflection on the optical elements M1 and M2 and finally strikes the wafer 24. The wavelength of the exposure radiation 34 in the present case is in the extreme ultraviolet wavelength range (EUV), e.g. at about 13.5 nm or 6.8 nm, but in other embodiments of the projection exposure apparatus 10 may also be used in the UV wavelength range, e.g. at 248 nm or 193 nm. The optical elements M1 and M2 are configured as mirrors in the case shown. Depending on the wavelength of the exposure radiation 34, the optical elements of the projection lens 30 may be embodied as lenses and / or as mirrors. The mask 16 and the wafer 24 are each arranged displaceably transversely to the beam direction of the exposure radiation 34 on a slide carriage 18 or 26 relative to the respective base 20 or 28 of the mask shift stage 14 or the wafer shift platform 22. During the exposure process, mask 16 and wafer 24 are displaced in opposition to each other, thereby performing a scanning movement.

The stability of the beam path of the exposure radiation 34 during the imaging process is effected by means of the above-mentioned sensor frame 102, which is designed as a rigid reference structure. The sensor frame is by means of vibration dampers 106-1 and 106-2 in the form of shock absorbers, which are also referred to as insulators, on the frame frame 12 of the projection exposure apparatus 10, in particular on the support frame 32 of the Projektionsobichtungsanlage. jektivs 30 hung up. The positions of the mask shuttle stage 14, the optical elements M1 and M2, and the wafer transfer stage 22 are continuously referenced to the sensor frame 102 by means of distance measuring devices 48-1 to 48-4 during the exposure operation and held in stable positional relation to the sensor frame 102 by appropriate action.

Specifically, the distance measuring devices 48-1 to 48-4 in the imaging mode continuously measure the relative position of the mask shuttle stage 14, the optical elements M1 and M2 and the wafer transfer platform 22 in one or more dimensions at respective measurement points on the sensor frame 102. 1 to 108-4 are transmitted to a control device 116, which, with changes in the distance values 108-1 to 108-4 control signals 118-1 to 118-4 to the Maskverschiebebühne 14, the actuators 36-1 and 36-2 of the optical elements M1 and M2 as well as the Waferverschiebebühne 22 transmitted. The control signals 118-1 to 118-4 serve to correct the positional changes in the beam path of the exposure radiation 34 determined on the basis of the measured distance values 108-1 to 108-4. In other words, the control signals 118-1 to 118-4 effect respective adjustment processes in the mask shift stage 14, the actuators 36-1 and 36-2 as well as the wafer transfer stage 22, whereby the changes in the distance values 108-1 to 108-4 are compensated again. Thus, during an exposure process, the respective positional relationship of the mask 14, the optical elements M1 and M2 and the wafer to the respective measurement points on the sensor frame 102 is kept stable.

As already mentioned above, a vibration excitation 40, typically in the range between 0.1 Hz and 10 Hz, may cause the shape of the sensor frame 102 to move between the undeformed shape shown in FIG. 6 and the deformed shape shown in FIG her oscillates. As a result, the measuring points of the distance measuring devices 48-1 to 48-4 on the sensor frame 102 shift relative to one another, ie in the deformed shape illustrated in FIG. 7 the relative positional relationship of the measuring points is added. Other than in the illustrated in Fig. 6 undeformed shape. Without further compensation for this effect, due to the respective referencing of the mask transfer stage 14, the optical elements M1 and M2 and the wafer transfer stage 22 to the sensor frame 102, this would result in the deformation of the sensor frame 102 being a relative shift of said elements, in particular of the optical elements M1 and 2, to each other. This in turn would result in a lateral aberration 35, as illustrated in FIG. 7 with reference to the beam path of the exposure radiation 34. According to one aspect of the invention, the described deformation effect of the sensor frame 102 is taken into account in the stabilization control of the projection exposure apparatus 10 and thus eliminates or at least minimizes its influence on the lateral imaging stability. For this purpose, the projection objective 30 according to FIGS. 6 and 7 comprises a measuring device 46 with activity sensors 104-1 and 104-2 and an evaluation device 52. Each of the vibration dampers 106-1 and 106-2 is one of the activity sensors 104-1 and 104, respectively -2 in the form of a distance measuring device for measuring an activity parameter of the respective vibration damper 106-1 and 106-2, respectively, in the form of a deformation value 112-1 or 112-2 indicative of the mechanical deformation of the vibration damper. According to one embodiment, the activity sensors 104-1 and 104-2 are each designed as interferometric distance measuring device 48 according to FIG. 2. The deformation values 112-1 and 112-2 of the vibration dampers 106-1 and 106-2 are transmitted to the evaluation device 52 during the exposure operation. In a first evaluation unit 52a, an acceleration value 114 is determined from the deformation values 112-1 and 112-2, which quantifies acceleration forces acting on the sensor frame 102.

From the acceleration value 114 representing a deformation parameter of the sensor frame 102, a second evaluation unit 52b then calculates a deformation shape 54 resulting therefrom for the sensor frame 102. The calculation is based on finite element modeling (FE modeling). In particular, the second evaluation unit 52b may use a transformation matrix determined by means of an FE model in the calculation of the deformation form. According to a further embodiment, instead of the activity sensors 104-1 and 104-2 of the vibration damper 106-1 or 106-2, one or more acceleration sensors may also be provided for the direct measurement of the acceleration value 114.

The deformation form 54 determined by the second evaluation unit 52b is forwarded to a correction device 56. This in turn determines corrector signals 58-1 to 58-4 in the form of correction values for the control signals 116-1 to 116-4 and transmits these to the control device 116. The correction signals 58 take into account the changes in position resulting from the changed shape of the sensor frame 102 the measuring points of the distance measuring devices 48-1 to 48-4 in the evaluation of the distance values 108-1 to 108-4 determined by these. In other words, the correction signals 58-1 to 58-2 serve the control signals 118-1 to 118-4 to the mask transfer stage 14, the actuators 36-1 and 36-2 of the optical elements M1 and M2, and the wafer transfer stage 22 to adapt to the respective current deformation shape 54 to avoid a lateral aberration.

This can be done according to an embodiment variant in that a respective change in position of the optical elements M1 and M2, and possibly also of the translation stages 14 and 22, which would result from referencing to the sensor frame 102, is determined from the transmitted deformation shape 54 and the control signals 18-1 to 118-4 are adjusted by means of the correction signals 58-1 to 58-4 in such a way that said positional changes of the optical elements M1 and M2 are corrected directly. According to a further embodiment, the transmitted deformation shape 54 can also be calculated by calculating the resulting positional changes of the optical elements M1 and M2, and possibly also of the translation stages 14 and 22, and the resulting change in the beam path of the exposure radiation 34 in the projection objective 30 a resulting lateral imaging errors are determined. In this case, the correction signals 58-1 to 58-4 cause only the change of the control signal 18-1 and / or 118-4 to the mask shuttle 14 and the wafer transfer stage 22 to execute a correction movement 62 serving to correct the lateral aberration 55 or 64 in the form of a lateral displacement of the mask 6 or of the wafer 24. The two variants for compensating a transmitted deformation shape can also be combined with each other.

The evaluation units 52a and 52b shown separately in FIGS. 6 and 7 can also form a common functional unit together with the correction device 56, which comprises a plurality of deformation values 112 as input parameters, for example twenty-four input parameters at six deformation values per vibration damper 106 and four vibration dampers used generates correction signals 58 comprising a plurality of correction values by means of a transformation matrix based on an FE model. The correction signals 58 may be e.g. Correction values for each of six rigid body degrees of freedom for the actuation of the optical elements of the projection lens 30 and the translation stage 14 and 22, respectively. In a case where the projection lens 30 has ten correspondingly operable optical elements, the correction signals include (10 + 2) × 6 = 72 correction values. The transformation matrix determined by means of the FE model is a 72 × 24 matrix in the example given with 24 inputs and 72 outputs. A transformation matrix of such a size allows a real-time calculation of the correction signals 58 with regard to the frequency of the vibration excitation 40.

FIG. 8 illustrates another embodiment of a microlithographic projection exposure apparatus 10. This differs from the projection exposure apparatus according to FIGS. 6 and 7 in that the measuring device 46 additionally comprises, in addition to the activity sensors 104-1 and 104-2, a distance measuring device of the type illustrated in FIG. 2 for determining the deformation parameter of FIG Sensor- frame 102. The distance measuring device 148 serves to measure changes in the length of the sensor frame 102 in a direction transverse to the beam path of the exposure radiation 34, ie, parallel to the x direction according to the coordinate system indicated in FIG. 8. Compared to the distance measuring device 48 according to FIG. 2, the measuring head 67 of the distance measuring device 148 is tilted. To compensate for this tilt, the distance measuring device 148 additionally has a deflecting mirror 150 with which the measuring radiation 67 emanating from the measuring head 67 is directed onto the splitting element 70.

The measured value determined by the distance measuring device 148 indicates the distance between the reflector 80 and the splitting element 70. While the reflector 80 in the left region of the sensor frame 102 is attached to the latter, the splitting element 70 is fastened to the latter in the right region of the sensor frame 102. Thus, variations of the measured value over time describe the above-mentioned changes in the length of the sensor frame 102 parallel to the x-direction. The measured values of the distance measuring device 148 are transmitted to the evaluation device 52 as further deformation values 112-3 and taken into account in the determination of the deformation shape 54 of the sensor frame 102. According to a further embodiment of the projection exposure apparatus 10, the measuring device 46 comprises no activity sensors 104-1 and 104-2 but only the distance measuring device 148 and possibly further distance measuring devices for measuring changes in the length of the sensor frame 102 in other coordinate directions.

The above description of exemplary embodiments is to be understood by way of example. The disclosure thus made makes it possible for a person skilled in the art on the one hand to understand the present invention and the associated advantages, and on the other hand also includes obvious modifications and modifications of the structures and methods described in the understanding of the person skilled in the art. Therefore, all such modifications and modifications as far as they are within the scope of the invention as defined in the appended claims, and equivalents are covered by the scope of the claims.

LIST OF REFERENCE NUMBERS

10 projection exposure machine

12 frame

14 Mask Shifting Platform

16 mask

18 sliding carriages

20 base

22 wafer transfer platform

24 wafers

26 sliding carriage

28 base

30 projection lens

31 base frame

32 carrier frame

32a, 32c side elements

32b, 32d cross elements

31-1 and 32-2 support frames

34 exposure radiation

34-1 incoming exposure radiation

34-2 exposure radiation in the imaging beam path

35 lateral aberration

36, 36-1 and 36-2 actuator

38 tilting axis

40 vibration excitation

42 frame deformation

44 tilting

46 measuring device

48 Distance measuring device

50 distance value

52 evaluation device

52 and 52b evaluation units 54 deformation form

56 Correction device

58-1 to 58-4 correction signals

60, 62 and 64 correction movements

66 incoming measuring radiation

67 measuring head

68 beam splitter

69 optical axis

70 cleavage element

71 Fizefläche

72 measuring beam

74 reference beam

75 measuring section

76 Camera Lens

78 detector

80 sliding reflector

82 streaks

84 multi-striped interference pattern

85 local disturbances

86 corrected multi-strip interference pattern

88 Retroreflector

89 Measuring radiation module

90 G mirror

91 pressure gauge

93 measuring radiation source

94 evaluation unit

95 focusing optics

96 aperture

97 focusing optics

98 expanded measuring beam

102 sensor frame

104-1, 104-2 activity sensors 106 vibration damper

108-1 to 108-4 distance values

110 shift

112-1, 112-2, 112-3 Deformation values 114 Acceleration value

116 control device

118-1 to 118-2 control signals

A, B, C, D reference points

M1, M2 optical elements

148 distance measuring instrument

150 deflection mirror

Claims

claims

1. Interferometric distance measuring device for measuring an optical path length difference between a reference beam path and a measuring beam path in a volume of gassed gases, wherein a diameter of the measuring beam path is at least partially at least 0.1 cm.

2. Interferometric distance measuring device according to claim 1,

in which the diameter of the measuring beam path is at least in sections at least 1 cm, in particular at least 3 cm.

3. Interferometric distance measuring device according to claim 1, which is configured to generate a multi-strip interference pattern by superimposing a measuring radiation guided in the measuring beam path with a reference beam guided in the reference beam path, and comprising an evaluation unit which is configured to local disturbances in the multi-strip interference pattern by means of a Correlation filter correct.

4. Interferometric distance measuring device according to one of the preceding claims,

which comprises a retroreflector for back reflection of a measurement radiation passing through the measurement beam path, wherein the normal to the retroreflector is tilted by at least 1 mrad relative to the propagation direction of the measurement radiation.

5. Interferometric distance measuring device according to one of the preceding claims,

in which the measuring beam path has at least two sections tilted relative to one another.

Interferometric distance measuring device according to one of the preceding claims,

in which the measurement beam path comprises a measurement path in which the measurement beam path is not superimposed by the reference beam path, the measurement path being at least 0.5 m in length.

7. Interferometric distance measuring device according to one of the preceding claims,

which comprises a pressure gauge for measuring a pressure in the region of the measuring beam path and the interferometric distance measuring device is configured to take into account the pressure measured value in the determination of the optical path length difference.

8. A microlithographic projection exposure apparatus comprising a projection lens for imaging mask patterns on a substrate by means of exposure radiation and an interferometric distance measuring apparatus according to any one of the preceding claims.

The microlithographic projection exposure apparatus of claim 8, wherein the projection objective comprises:

optical elements for guiding the exposure radiation,

a support frame to which the optical elements are fastened by means of actuators,

- A sensor frame, which is mounted by means of a vibration damper on the support frame, and

Position sensors, which are configured to measure the respective position of the optical elements with respect to the sensor frame during operation of the projection exposure apparatus and to control the actuators for correcting measured position changes,

wherein the distance measuring device is configured to determine during the operation of the projection exposure apparatus at least one deformation parameter characterizing a deformation of the sensor frame.

10. A method for interferometrically measuring a length of a measuring section which passes through a volume of gassed gases, comprising the steps of:

- Radiating the measuring section with a measuring beam whose diameter is at least partially at least 0.1 cm, and

- Interferometric measurement of a path length difference between a reference beam path and a measurement path comprising the measuring beam path.

11. The method according to claim 10,

in which the interferometric measurement of the path length difference comprises evaluating a multi-strip interference pattern generated by superposing a measuring radiation guided in the measuring beam path with a reference radiation guided in the reference beam path and correcting local interferences in the multi-strip interference pattern by means of a correlation filter when evaluating the multi-strip interference pattern.

12. A projection exposure apparatus for microlithography comprising a projection objective for imaging mask structures onto a substrate by means of exposure radiation, the projection objective comprising:

optical elements for guiding the exposure radiation,

a sensor frame, which is mounted on the carrier frame by means of a vibration damper,

- Position sensors, which are configured to measure during operation of the projection exposure system, the respective position of the optical elements with respect to the sensor frame and to control the actuators to correct measured changes in position, and

a measuring device for monitoring a lateral imaging stability of the projection lens, which is configured during operation of the projection jektionsbelichtungsanlage to determine at least one, a deformation of the sensor frame characterizing deformation parameters.

13. A projection exposure apparatus according to claim 12,

wherein the measuring device comprises an activity sensor for measuring an activity parameter of the vibration damper and an evaluation device for determining the deformation parameter from the activity parameter.

14. A projection exposure apparatus according to claim 13,

wherein the activity sensor comprises a distance sensor for measuring a mechanical deformation of the vibration damper.

15. A projection exposure apparatus according to any one of claims 12 to 4, wherein the measuring device comprises an acceleration sensor for measuring an acceleration of the sensor frame.