DE102017221023A1 - DEVICE FOR MONITORING AT LEAST ONE TIP AT LEAST ONE MIRROR - Google Patents

Abstract

The present invention relates to a method and a device for monitoring at least one tilted position of at least one mirror (30) with at least one set of discrete light sources (20) and at least one detection device (5) which detects the light of the light sources of the set of discrete light sources reflected by the mirror wherein the detection device comprises a sensor (51) and a lens (50), and wherein the device further comprises a transmission filter (4) with locally varying transmission, thus between mirror (30) and detection device (5) or in the detection device arranged such that the light of the light sources reflected by the mirror passes through the transmission filter, wherein the set of discrete light sources (20) is configured such that the discrete light sources can be switched on and off in sequence, and wherein the detection device is designed and is arranged that at the to be supervised ends of the mirror or the set of discrete light sources can be imaged onto the sensor of the detection device.

Description

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to a device and a method for monitoring at least one tilted position of at least one tiltable mirror.

STATE OF THE ART

Microlithography projection exposure equipment is used for the production of microstructured components by means of a photolithographic process. In this case, a structure-carrying mask, the so-called reticle, with the aid of a light source unit and a BeLichtungsoptik beLichtet and imaged using a projection optics on a photosensitive layer. For this purpose, the light source unit provides a radiation which is processed in the illumination optics for illuminating the reticle. The illumination optics serve to provide uniform out-of-plane illumination with a predetermined angle-dependent intensity distribution at the location of the structure-supporting mask. For this purpose, various suitable optical elements are provided within the BeLichtungsoptik.

The so-structured structure-bearing mask is imaged onto a photosensitive layer with the aid of projection optics. In this case, the minimum structure width that can be imaged with the aid of such projection optics is determined inter alia by the wavelength of the radiation used. The smaller the wavelength of the radiation, the smaller the structures can be imaged using the projection optics. For this reason, it is advantageous to use radiation having a wavelength in the range of 5 nm to 15 nm. Radiation in this wavelength range is called extreme ultraviolet (EUV) light.

In illumination systems operating in corresponding projection exposure systems, for example in the wavelength range of the extreme ultraviolet (EUV) spectrum, ie at wavelengths in the range of, for example, 13 nm, facet mirror arrays are used in a field plane consisting of a plurality of tiltable mirrors, the field facet mirrors or mirror facets , The mirror facets, which can be tilted about at least one axis, but usually about two axes arranged transversely to one another, determine the intensity distribution in a pupil plane, which in turn is optically conjugate to the entrance pupil plane of the projection optics, so that the intensity distribution of the radiation in the pupil plane of the illumination system determines the angle-dependent intensity distribution the radiation in the area of the object field determined.

For this reason, the setting of the mirror facets, ie their orientation or orientation, must be selected exactly. Consequently, it is also important that the adjustment or alignment of the mirror, ie its tilt angle about one or more axes of rotation, can be determined exactly. Therefore, methods and devices for determining and monitoring the tilt angles of mirror arrangements are already described in the prior art. Examples are in the DE 10 2009 009 372 A1 . WO 2010/094658 A1 . WO 2009/015845 A1 . US 2012 / 0293784A1 . WO 2008/095695 A2 and DE 10 2013 217 655 A1 given.

However, despite the proposed solutions, there is still a need for a simple, effective and reliable monitoring system which can detect the tilt of the tiltable mirror facets or mirrors generally quickly and with high precision to be used in control circuits for tilting the field facets or mirrors. In addition, care must be taken that the corresponding measuring method or the corresponding measuring system with regard to the vacuum compatibility, the material compatibility, etc. can be integrated into a projection exposure apparatus and in particular into a lighting system thereof.

DISCLOSURE OF THE INVENTION

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a monitoring device for determining and / or monitoring the position and / or orientation or tilting position of, in particular, tiltable To provide mirrors and a corresponding method for this purpose, as well as to provide a projection exposure apparatus and in particular a lighting system, preferably an EUV projection exposure apparatus, which has a suitable device for monitoring the tilting position of mirrors. In addition, a corresponding operating method for operating such a device should be specified. The corresponding devices and methods are to allow a high-precision and rapid monitoring of the alignment of mirrors and be easily integrated into a projection exposure system.

TECHNICAL SOLUTION

This object is achieved with a device for monitoring the tilted position of at least one mirror with the features of claim 1 and a method having the features of claim 11 and a projection exposure apparatus with the features of claim 14. Advantageous embodiments are the subject of the dependent claims.

In order to monitor at least one tilted position of at least one mirror, in particular a mirror which can be tilted about at least one axis of rotation, the present invention proposes a device which has at least one set of discrete light sources and at least one detection device. The light of the light source arrangement comprising a set of discrete light sources is reflected by the mirror to be monitored into the detection device, the detection device having a sensor and an objective in order to detect the light reflected by the at least one mirror. In addition, the device according to the invention has a transmission filter with locally varying transmission, which is arranged between the mirror and the detection device or in the detection device. In this case, a transmission filter with locally varying transmission is understood as meaning a filter which permits a transmission of the reflected light which differs over the filter surface. Thus, it is possible to detect intensities of the reflected light beams corresponding to the passage point of the light beams through the transmission filter with the detection means, wherein different transmission points of the light beams through the transmission filter due to the origin of different light sources to a different intensity due to the locally varying transmission of the transmission filter the light beams detected by the detection device, so that at a known output intensity of the light beams generated by the light sources of the light source arrangement and a given reflectivity of the mirror, the passage point of the reflected light beams through the transmission filter can be determined due to the transmitted intensity. With the passage points through the transmission filter, the tilted position of the mirror or mirrors can be determined.

For this purpose, the detection device is designed and arranged in such a way that the mirror or set of discrete light sources (light source arrangement) is imaged onto the sensor of the detection device at a tilting position of the mirror to be monitored, so that the reflected light beams of the different light sources of the light source arrangement as separate light intensities corresponding to the transmission can be detected by the transmission filter. In addition, the device is constructed so that the discrete light sources of the light source assembly can be turned on and off in turn.

Accordingly, in a method for monitoring at least one tilt position of at least one mirror, in particular a mirror tiltable about a rotation axis, the light sources of a set of a plurality of discrete light sources are switched on and off in sequence, so that in a detection device with a sensor that of the light emitted by the light sources, which is reflected at the mirror to be monitored, can be detected in order to determine the intensity of the incident light on the sensor. Since between the mirror or mirrors to be monitored and the detection device or in the detection device, a transmission filter with locally varying transmission is arranged, the rays reflected from the mirror at the same output intensity of the light sources depending on the passage point through the transmission filter to a different intensity. On the basis of the spatially resolved intensities of the reflected light, the tilted position of the mirror can be determined.

By a possible restriction of the tilting angle range to be monitored to a predetermined tilting position of the mirror or mirrors, a particularly good measuring accuracy with regard to the position and / or orientation of the mirror or the tilted position of the mirror or mirrors can be achieved.

The light sources of the set of discrete light sources that can be switched on and off, which lead to different reflection angles at the mirror to be monitored and thus to different transmission points through the transmission filter with locally varying transmission, can be arranged in any two-dimensional pattern, with monitoring of the tilted position one or more mirrors a rotation axis, the discrete light sources may be arranged linearly along a direction. Preferably, however, the discrete light sources may be arranged in a two-dimensional pattern along at least one first direction and at least one second direction perpendicular to the first direction so that the tilt position of the mirror or mirrors to be monitored may be monitored about two independent axes of rotation. In particular, the light sources can be arranged in a cross shape.

The transmission filter, which has a locally varying transmission, that is to say a transmission varying over the transmission surface, can be embodied such that the varying transmission varies in at least one direction, for example if only the tilted position about an axis of rotation is to be monitored. Preferably, however, the transmission filter can have a varying transmission along two independent spatial directions, wherein the corresponding transmission characteristics can be superimposed. The transmission filter may in particular have a first profile of a varying transmission in a first direction (x-direction) and a second profile of a varying transmission of a second direction (y-direction), which may in particular run perpendicular to the first direction.

For example, the transmission may increase or decrease in accordance with the first and / or second transmission profile from the edge of the transmission filter to the center of the transmission filter, and the transmission profiles may in particular have a sinusoidal or triangular profile.

Further, the transmission filter may be formed so that the transmission filter for the light to be filtered has a locally varying transmission with respect to one or more characteristics of the light to be filtered. Thus, a property of the light may be the wavelength of the light, so that a locally varying transmission in the transmission filter is set correspondingly for a certain wavelength of the light. Another possible property, according to which the light is filtered by the transmission filter, may be the polarization of the light, so that linearly polarized light, for example, is filtered in one direction.

The locally varying transmission according to one or more characteristics of the light can be realized along two mutually perpendicular directions in the transmission filter so that, for example, red light is filtered differently in a first direction (x-direction) while being arranged in a direction perpendicular to the first direction second direction (y direction) blue light with different transmission is filtered. This allows the monitoring of tilt positions to be separated by different axes of rotation.

A simple solution of a transmission filter, however, is a gray gradient filter which, regardless of the wavelength of the light in the case of white light, varies the transmitted intensity depending on the transmittance.

If a plurality of mirrors are to be monitored, for example, in a multi-mirror array (MMA) arranged side by side, for example, in one or more rows and / or columns, the detector may detect the reflected light from multiple or all mirrors simultaneously. In addition, several detection devices can be provided.

Multiple detectors and / or multiple sets of discrete light sources may also be used to monitor not only a particular tilt position of the mirror or mirrors when monitoring a mirror or multi-mirror array, but multiple different tilt positions.

The detection device may comprise a surface sensor, such as a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor with which a spatially resolved determination of the incident light intensity is possible.

The device may further comprise an evaluation unit which evaluates the spatially resolved intensities detected by the sensor and automatically determines a tilted position of the monitored mirror, wherein additionally the determined tilt position can be stored with a desired tilt position, which can be stored in the evaluation unit or a corresponding memory. compares to detect deviations. The evaluation unit can in this case be realized, in particular, by a data processing system which has been set up by programming.

The possible deviation of a tilted position of the monitored mirror from a desired tilting position can be used in a control and / or regulating device for controlling and / or regulating the tilted position of the at least one monitored mirror.

The detection device can detect the reflected light in synchronism with the switching times of the light sources, and the light sources or the sensor for detecting the incident light intensity can be operated at a frequency of up to 10,000 Hz, or detections per second.

list of figures

• 1 eine Darstellung einer erfindungsgemäßen Vorrichtung,
• 2 eine Darstellung eines Teils einer erfindungsgemäßen Vorrichtung mit einer detaillierten Darstellung eines Transmissionsfilters und
• 3 eine Darstellung einer EUV - Projektionsbelichtungsanlage, bei welcher eine Vorrichtung gemäß den 1 und 2 eingesetzt werden kann.

The accompanying drawings show in a purely schematic manner in FIG

• 1 a representation of a device according to the invention,
• 2 a representation of a part of a device according to the invention with a detailed representation of a transmission filter and
• 3 a representation of an EUV - projection exposure apparatus, in which a device according to the 1 and 2 can be used.

EMBODIMENTS

Further advantages, characteristics and features of the present invention will become apparent in the following detailed description of the embodiments. However, the invention is not limited to these embodiments.

The 1 shows an embodiment of a device according to the invention 1 for monitoring the tilting position of mirrors 30 , In the embodiment shown the 1 are four mirrors 30 arranged in two rows and two columns, their tilted position by the device 1 should be monitored. For this purpose, the device 1 a set of discrete light sources (light source arrangement) 2 with several discrete light sources 20 on, which may be formed for example by LEDs.

The light sources 20 can be arranged differently depending on whether the tilting of the mirror is to be monitored only with respect to a tilt about a tilt axis or two independent tilt axes. When monitoring only a single tilting axis, it is possible to use the light sources 20 in the light source arrangement 2 to provide in a linear arrangement, while monitoring the tilt position by two independent tilt axes, a flat arrangement of the light sources 20 in a pattern is advantageous. In the embodiment shown the 1 are five light sources 20 arranged in a cross shape.

The light or the light rays 21 the light sources 20 be from the mirrors 30 in the tilted position of the mirror to be monitored 30 in a detection device 5 that reflects a lens 50 and a sensor 51 with which the light reflected at the mirrors 30 22 can be detected.

The mirror arrangement 3 with the four mirrors 30 in two rows and two columns is merely an example and the device 1 for monitoring the tilting position of the mirrors 30 the mirror arrangement 3 can be any number of mirrors in any arrangement of mirrors 30 in the mirror arrangement 3 include.

The detection device 5 with the sensor 51 is so with respect to the mirror assembly 3 and the light source assembly 2 arranged so that either the mirrors 30 the mirror arrangement 3 sharp on the sensor 51 and the detection surface provided there are imaged or the light sources 20 the light source arrangement 2 ,

Between the mirror assembly 3 and the detection device 5 is a transmission filter 4 provided, the one above the transmission surface different transmission of the reflected light 22 causes. In the embodiment shown is a Grauverlaufsfilter in the white light from the light sources 20 according to the localized transmission behavior of the transmission filter 4 different intensities of the reflected light can happen.

The reflected light 22 the different light sources 20 penetrates the transmission filter 4 in different places, because the light rays 21 the light sources 20 at different angles of incidence on the mirrors 30 incident. Due to the different transmission through the transmission filter 4 Depending on the local change in the transmission across the transmission filter can be compared with that of the sensor 51 determined light intensity of the different light sources 20 reflected light 22 the tilted position of the corresponding mirror 30 be determined.

Because the reflected light 22 several mirrors 30 simultaneously in the detection device 5 can be detected if several or all mirrors 30 the mirror arrangement 3 through the lens 50 on the sensor surface of the sensor 51 can be mapped, multiple mirrors 30 be monitored in parallel with a detection device.

To prevent the reflected light 22 from different sources of light 20 in the detection of the intensity of the reflected light 22 in the sensor 51 influence each other, become the light sources 20 the light source arrangement 2 turned on and off one after the other, so that in turn the light rays 21 the different light sources 20 at the respective mirrors 30 reflect and the intensities of the reflected light rays 22 after passing the transmission filter 4 with the sensor 51 be detected, wherein the detection of the light intensity with the sensor 51 synchronous to the switching of the light sources 20 he follows.

The 2 shows in a similar representation as 1 a schematic view of a portion of a device according to the invention, but with the transmission filter is shown in greater detail. Besides, it's just a mirror 30 shown whose tilt position is to be monitored. This mirror 30 the embodiment of the 2 is also not flat, but curved as a parabolic mirror. In this case, the detection device becomes 5 (not in 2 shown) so that not the mirror 30 sharp on the sensor surface of the sensor (not in 2 shown), but the light source arrangement 2 so that so the sensor surface of the sensor 51 and the area in which the areal pattern of the light sources 20 is formed, in conjugate levels of the device 1 are arranged.

As is clear from the 2 results, is the transmission filter 4 formed in the embodiment shown so that both in the x-direction and in the y-direction, the transmission from the center of the transmission filter 4 to the edge of the transmission filter 4 decreases with a sinusoidal shape, as the diagrams on the sides of the transmission filter 4 demonstrate. Accordingly lies with the transmission filter 4 of the 2 in the center the maximum transmission demands, while at the corners the minimum transmission of the reflected light through the transmission filter 4 he follows.

As is clear from the 2 furthermore, the crosswise arranged light sources become 20 the light source arrangement 2 imaged in the sensor of the detection device and the mirror 30 reflected light rays 22 . 22 ' penetrate the transmission filter 4 at the puncture points 40 , which likewise have a cross-shaped arrangement. Due to the different position of the puncture points 40 the reflected light rays 22 . 22 ' become the reflected light rays 22 . 22 ' through the transmission filter 4 filtered differently, so that the sensor different intensity values of the transmitted and reflected light beams 22 . 22 ' detected.

The spatially varying transmission can be described here with $$\text{T}\left(\text{x}\text{, y}\right)=\text{A}+\text{B * cos}\left(\text{x}\right)+\text{C * sin}\left(\text{y}\right)$$

$$\text{i2}=\text{a}+\text{b*cos}\left(\text{x0}\mathrm{+}\Delta \text{x}\right)+\text{c*sin}\left(\text{y0}\right)$$

$$\text{i3}=\text{a}+\text{b*cos}\left(\text{x0}\mathrm{-}\Delta \text{x}\right)+\text{c*sin}\left(\text{y0}\right)$$

$$\text{i4}=\text{a}+\text{b*cos}\left(\text{x0}\right)+\text{c*sin}\left(\text{y0}\mathrm{+}\Delta \text{y}\right)$$

$$\text{i5}=\text{a}+\text{b*cos}\left(\text{x0}\right)+\text{c*sin}\left(\text{y0}\mathrm{-}\Delta \text{y}\right)$$

With the location of the puncture points 40 the one at the mirror 30 reflected rays 22 . 22 ' at the points (x0, y0), (x0 + Δx, y0), (x0-Δx, y0), (x0, y0 + Δy) and (x0, y0-Δy) on the transmission filter the five following intensity values result $$\text{i1}=\text{a}+\text{b * cos}\left(\text{x0}\right)+\text{c * sin}\left(\text{y0}\right)$$

$$\text{i2}=\text{a}+\text{b * cos}\left(\text{x0}\mathrm{+}\Delta \text{x}\right)+\text{c * sin}\left(\text{y0}\right)$$

$$\text{i3}=\text{a}+\text{b * cos}\left(\text{x0}\mathrm{-}\Delta \text{x}\right)+\text{c * sin}\left(\text{y0}\right)$$

$$\text{i4}=\text{a}+\text{b * cos}\left(\text{x0}\right)+\text{c * sin}\left(\text{y0}\mathrm{+}\Delta \text{y}\right)$$

$$\text{i5}=\text{a}+\text{b * cos}\left(\text{x0}\right)+\text{c * sin}\left(\text{y0}\mathrm{-}\Delta \text{y}\right)$$

With known locally varying transmission of the transmission filter 4 and the known arrangement of the light sources 20 in the light source arrangement 2 can the puncture point 40 (x0, y0) are uniquely determined. From this can on the tilted position of the mirror 30 closed or these are determined.

The larger the transmission filter 4 is and thus a larger angular range of tilting position of the mirror 30 can be detected, the lower the measurement accuracy, since in this case the transmission filter between the extreme values 100% transmission and 0% transmission must have a shallower transmission gradient. A smaller gradient of the transmission of the transmission filter 4 however leads to a reduced measuring accuracy. Accordingly, it is advantageous not to use the device of the invention for determining any tilt angle, but preferably for monitoring a certain, predetermined tilt angle so that the angle monitoring range is very small and thus the measurement accuracy can be set very high. For example, the tilt angle monitoring range can be 1% of the total tilt angle range, so that the device according to the invention and the method according to the invention are very well suited for monitoring a possible change with time of a fixed predetermined tilt position of one or more mirrors.

Should with the in the 1 and 2 Device shown multiple tilt positions of one or more mirrors 30 can be monitored, so either more light source arrangements 2 (not shown) or other detection devices 5 (also not shown) are provided.

The 3 shows an EUV projection exposure system 100 with an EUV light source 102 , a lighting module 103 and a projection lens 104 , With such a projection exposure system 100 can be a reticle 105 with from the lighting module 103 recycled light of the EUV - light source 102 be lit, with one on the reticle 105 structure through the projection lens 104 on the wafer 106 reduced size, so that a corresponding structure is microlithographically on the wafer 106 can be generated.

A device according to the invention for monitoring the tilting position of mirrors can be provided in a corresponding EUV projection exposure apparatus 100 for monitoring the mirror position and orientation of different mirrors are used, in particular of multi-mirror fields (MMA Multi Mirror Arrays), in particular in the lighting system 103 can be used. With the device according to the invention, an automated monitoring of the positioning and orientation of mirrors in EUV projection exposure systems or projection exposure systems can generally be realized. This allows to determine over the course of time possible changes in the position and / or orientation of the mirror or mirrors.

Although the present invention has been described in detail with reference to the embodiments, it will be apparent to those skilled in the art that the invention is not limited to these embodiments, but rather modifications are possible in the manner that individual features omitted or other combinations of features can be realized as long as the scope of protection of the appended claims is not abandoned. In particular, the present disclosure includes all combinations of the features presented.

LIST OF REFERENCE NUMBERS

1

contraption

2

Light source arrangement

20

light source

21

beam of light

22, 22 '

reflected light beam

3

mirror arrangement

30

mirror

4

transmission filter

40

Intersection point

5

detector

50

lens

51

sensor

100

EUV - projection exposure system

102

EUV - light source

103

lighting system

104

projection lens

105

reticle

106

wafer

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102009009372 A1 [0005]
• WO 2010/094658 A1 [0005]
• WO 2009/015845 A1 [0005]
• US 2012/0293784 A1 [0005]
• WO 2008/095695 A2 [0005]
• DE 102013217655 A1 [0005]

Claims (14)

Device for monitoring at least one tilted position of at least one mirror (30) with at least one set of discrete light sources (20) and at least one detection device (5) which detects the light of the light sources of the set of discrete light sources reflected by the mirror, the detection device comprising a sensor ( 51) and a lens (50), and wherein the device further comprises a transmission filter (4) with locally varying transmission, which is arranged between mirror (30) and detection device (5) or in the detection device, that of the mirror reflected light of the light sources passes through the transmission filter, characterized in that the set of discrete light sources (20) is formed so that the discrete light sources can be switched on and off in turn, and wherein the detection means is arranged and arranged such that at the to be monitored tilt position of the mirror de Mirror or the set of discrete light sources are imaged on the sensor of the detection device. Device after Claim 1 , characterized in that the light sources (20) of the set of discrete light sources are arranged in a two - dimensional pattern. Device according to one of the preceding claims, characterized in that in a set of discrete light sources (20) at least two, preferably three or more light sources are arranged along a first direction and at least two, preferably three or more light sources along a second direction, the first Direction is perpendicular, the light sources are arranged in particular cross-shaped. Device according to one of the preceding claims, characterized in that the transmission filter (4) has a varying transmission in at least one direction or a varying transmission in two independent spatial directions. Device according to one of the preceding claims, characterized in that the transmission filter (4) in a first direction (X - direction) has a first course of varying transmission and in a second direction (Y - direction) perpendicular to the first direction has a second course of a has varying transmission, wherein the first and / or second course have a from the center of the transmission filter to the edge of the transmission filter increasing or decreasing transmission, in particular a sinusoidal or triangular course. Device according to one of the preceding claims, characterized in that the transmission filter (4) is formed so that the transmission filter for the light with respect to one or more properties of the light has a locally varying transmission, in particular along two mutually perpendicular directions based on a varying transmission on different properties of the light, wherein in particular the transmission-determining properties of the light are the wavelength of the light or the polarization of the light. Device according to one of the preceding claims, characterized in that a plurality of mirrors (30) side by side, in particular in one or more rows and / or columns are arranged side by side and the detection means detects the reflected light from several or all mirrors simultaneously. Device according to one of the preceding claims, characterized in that a plurality of sets of discrete light sources (20) and / or a plurality of detection devices (5) are arranged in the device, each set of discrete light sources and each detection device being associated with a specific tilted position of the mirror. Device according to one of the preceding claims, characterized in that the sensor (51) is a CCD sensor or a CMOS sensor. Device according to one of the preceding claims, characterized in that the device comprises an evaluation unit, which determines from the sensor detected, spatially resolved intensities a tilted position of the monitored mirror and in particular compares with a stored desired position. Method for monitoring at least one tilted position of at least one mirror (30) about at least one axis of rotation, preferably with a device according to one of the preceding claims wherein at least one set of a plurality of discrete light sources (20) is provided, the light sources being switched on and off in turn, the light from the light sources being reflected by the mirror to be monitored into detection means (5) corresponding to that from the mirror detected light (22,22 ') of the light sources successively, wherein the detection means comprises a sensor (51) and a lens (50) which are formed and arranged relative to the set of discrete light sources and the mirror to be monitored, that in to be monitored tilt position of the mirror of the mirror or the set of discrete light sources are mapped to the sensor of the detection device, and wherein between the mirror and detection device or in the detection device further a transmission filter (4) is arranged with locally varying transmission, so that of the sensor at different Detected locations of the sensor, reflected e light has different intensities, and based on the spatially resolved intensities of the reflected light, the tilted position of the mirror is determined. Method according to Claim 11 , characterized in that the reflected light is detected in synchronism with the switching times of the light sources (20). Method according to Claim 11 or 12 , characterized in that the light sources (20) are switched with a switching frequency of up to 10 000 Hz. Projection exposure apparatus for microlithography with a device according to one of Claims 1 to 10 ,

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