ARRANGEMENT, METHOD AND COMPUTER PROGRAM PRODUCT FOR CALIBRATING FACET MIRRORS

Abstract

An arrangement (100), a method and a computer program product for system-integrated calibration of facet mirrors (18, 19) of a microlithographic illumination system (20). Beam paths (103) between a radiation source (101) and a radiation detector (102) are created by the facet mirrors (18, 19), with respectively only one pivotable micromirror (18, 19) of each facet mirror (18, 19) affecting said beam path. By methodically pivoting one of the micromirrors (18, 19) affecting the beam path (10), it is possible, based on the radiation detector (102), to find a specific optimal pivot position, the underlying orientation of the micromirror (18, 19) of which can also be calculated geometrically. By comparing the calculated orientation with the orientation ascertained by a tilt sensor on the micromirror (18, 19), it is possible to calibrate the tilt sensor or micromirror (18, 19) of the facet mirror (18, 19).

Claims

1. Arrangement for system-integrated calibration of facet mirrors of a microlithographic illumination system, comprising: at least one electromagnetic radiation-emitting radiation source and at least one radiation detector configured to detect the radiation emitted from the radiation source, wherein the facet mirrors are each configured as a micro-electromechanical system with a plurality of individually pivotable micromirrors with respective tilt sensors for ascertaining respective orientations of the micromirrors, wherein each of the sensors is arranged stationarily in a beam path of an illumination optical unit of the illumination system, wherein the electromagnetic radiation-emitting radiation source and the radiation detector are arranged stationarily such that a pivoting of the micromirrors of the facet mirrors yields a beam path from the radiation source to the radiation detector, involving only one micromirror of the micromirrors of each of the facet mirrors.

2. Arrangement according to claim 1, wherein the radiation detector is an intensity.

3. Arrangement according to claim 2, wherein the intensity detector comprises a stop and/or a bandpass filter adapted to the wavelength of the radiation source.

4. Arrangement according to claim 1, wherein the radiation source is an exposure radiation source of the illumination system and/or at least one radiation source that emits visible-range light.

5. Arrangement according to claim 4, wherein the radiation source is an extreme ultraviolet (EUV) exposure radiation source and/or at least one high power light-emitting diode or a laser that emits the light in the visible range

6. Arrangement according to claim 1, wherein the at least one radiation source and/or the at least one radiation detector are in each case arranged near an object plane of the illumination system or an intermediate focus of the exposure radiation source of the illumination system.

7. Arrangement according to claim 1, wherein the micromirrors of the facet mirrors are each pivotable about two non-parallel axes.

8. Method for calibrating the facet mirrors of a microlithographic illumination system using the arrangement according to claim 1, comprising: a) initially pivoting at least one of the micromirrors of one of the facet mirrors such that a beam path from the radiation source to the radiation detector is established, with only one micromirror per facet mirror affecting the beam path; b) methodically pivoting one of the micromirrors affecting the beam path at least over the pivot range in which the beam path is incident on and detected by the beam detector; c) ascertaining an optimal pivot position of the methodically pivoted micromirror with the beam detector, in the case of which position the beam path is incident most centrally on the micromirror that follows the methodically pivoted micromirror along the beam path or on the beam detector; d) determining an orientation of the methodically pivoted micromirror, as ascertained by a tilt sensor of the micromirror, for the ascertained optimal pivot position; e) comparing the orientation ascertained by the tilt sensor of the methodically pivoted micromirror with an orientation calculated from the geometric arrangement of the radiation source, the micromirrors affecting the beam path and the radiation detector; and f) recalibrating the tilt sensor of the micromirror based on the carried-out comparison.

9. Method according to claim 8, wherein said initial pivoting of the micromirrors of the facet mirrors affecting the beam path is followed by verifying the beam path desired by testing for a detector signal of the radiation detector, with the micromirrors affecting the provided beam path until radiation emanating from the radiation source is determined by the radiation detector.

10. Method according to claim 9, wherein said verifying comprises methodically pivoting the micromirrors affecting the provided beam path according to a given search pattern in the absence of a detector signal until radiation emanating from the radiation source above a given minimum intensity is determined by the radiation detector.

11. Method according to claim 8, wherein said ascertaining of the optimal pivot position comprises ascertaining a maximum of the intensity ascertained by the radiation detector, ascertaining the central maximum of the intensity ascertained by the radiation detector and/or ascertaining slopes of increase and decrease of the intensity when pivoting the one micromirror.

12. Method according to claim 8, wherein said ascertaining and said determining are carried out separately for each pivot axis of the micromirror being pivoted methodically.

13. Method according to claim 12, wherein said ascertaining and said determining are carried out immediately successively for each pivot axis of the micromirror being pivoted methodically.

14. Method according to claim 8, further comprising carrying out said initially pivoting, said methodically pivoting, said ascertaining, said determining and said comparing for a selected micromirror of the facet mirror being pivoted methodically, with at least three different beam paths.

15. Method according to claim 14, wherein the selected initially pivoted micromirrors are not located on a straight line.

16. Method according to claim 1, wherein an n-dimensional characteristic of the tilt sensor is adapted for recalibrating the tilt sensor, where n equals the number of axes about which the micromirror associated with the tilt sensor is pivoted.

17. Method according to claim 8, wherein, when micromirrors on the facet mirrors are calibrated with a defined pair of the radiation source and the radiation detector, the micromirrors of the facet mirror closer to the radiation source along the radiation path are calibrated first.

18. Method according to claim 8, wherein the calibration of individual ones of the micromirrors is implemented in parallel with a microlithographic exposure carried out with remaining ones of the micromirrors of the facet mirrors.

19. Method according to claim 8, further comprising spectrally and/or temporally decoupling given ones of at least one radiation that deviate from the exposure radiation source of the illumination system from the exposure by the exposure radiation source.

20. Arrangement comprising a control device programmed to carry out the method as claimed in claim 8.

21. Computer program product comprising program parts which, when loaded onto a computer or networked computers are programmed to carry out the method according to claim 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Now, the invention is described in exemplary fashion on the basis of advantageous embodiments, with reference being made to the attached drawings, in which:

[0057] FIG. 1: shows a schematic illustration of a microlithographic projection exposure apparatus comprising an arrangement according to the invention;

[0058] FIG. 2A: shows a schematic illustration of the calibration of a micromirror of a first facet mirror of the projection exposure apparatus of FIG. 1, and FIG. 2B shows an associated intensity distribution used in the calibration;

[0059] FIG. 3A: shows a schematic illustration of the calibration of a micromirror of a second facet mirror of the projection exposure apparatus of FIG. 1, and FIG. 3B shows an associated intensity distribution used in the calibration;

[0060] FIG. 4: shows a schematic flow chart of the method according to the invention;

[0061] FIGS. 5A, B: show schematic illustrations of alternative embodiments of the projection exposure apparatus of FIG. 1 using an additional radiation source in the vicinity of an intermediate focus (FIG. 5A) or in the vicinity of an object plane (FIG. 5B).

DETAILED DESCRIPTION

[0062] FIG. 1 shows a schematic meridional section of a microlithographic projection exposure apparatus 1. In this case, the projection exposure apparatus 1 comprises an illumination system 10 and a projection system 20, with the illumination system 10 being developed with an arrangement 100 according to the invention.

[0063] An object field 11 in an object plane 12 is illuminated with the aid of the illumination system 10.

[0064] To this end, the illumination system 10 comprises an exposure radiation source 13 which, in the illustrated exemplary embodiment, emits illumination radiation at least comprising used light in the EUV range, that is to say with a wavelength of between 5 nm and 30 nm in particular. The exposure radiation source 13 can be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It may also be a synchrotron-based radiation source. The exposure radiation source 13 can also be a free electron laser (FEL).

[0065] The illumination radiation emanating from the exposure radiation source 13 is initially focused in a collector 14. The collector 14 can be a collector with one or with a plurality of ellipsoidal and/or hyperboloidal reflection surfaces. The illumination radiation can be incident on the at least one reflection surface of the collector 14 with grazing incidence (GI), that is to say at angles of incidence of greater than 45, or with normal incidence (NI), that is to say at angles of incidence of less than 45. The collector 14 can be structured and/or coated on the one hand for optimizing its reflectivity for the used radiation and on the other hand for suppressing extraneous light.

[0066] The illumination radiation propagates through an intermediate focus in an intermediate focal plane 15 downstream of the collector 14. Should the illumination system 10 be constructed in a modular fashion, the intermediate focal plane 15 can be used as a matter of principle for the separationeven the structural separationof the illumination system 10 into a radiation source module, comprising the exposure radiation source 13 and the collector 14, and the illumination optical unit 16 described below. In the case of a corresponding separation, radiation source module and illumination optical unit 16 then jointly form a modularly constructed illumination system 10.

[0067] The illumination optical unit 16 comprises a deflection mirror 17. The deflection mirror 17 can be a plane deflection mirror or, alternatively, a mirror with a beam-influencing effect that goes beyond the purely deflecting effect. Alternatively or additionally, the deflection mirror 15 can be embodied as a spectral filter separating a used light wavelength of the illumination radiation from extraneous light having a wavelength that deviates therefrom.

[0068] The deflection mirror 17 is used to deflect the radiation emanating from the exposure radiation source 13 to a first facet mirror 18. Ifas in the present casethe first facet mirror 18 is arranged in a plane of the illumination optical unit 16 which is optically conjugate to the object plane 12 as a field plane, this facet mirror is also referred to as a field facet mirror.

[0069] The first facet mirror 18 comprises a multiplicity of micromirrors 18 that are individually pivotable about two perpendicular axes in each case, for the purpose of controllably forming facets which are each equipped with a tilt sensor (not depicted here) for ascertaining the orientation of the micromirror 18. Thus, the first facet mirror 18 is a micro-electromechanical system (MEMS system), as for example also described in DE 10 2008 009 600 A1.

[0070] A second facet mirror 19 is arranged downstream of the first facet mirror 18 in the beam path of the illumination optical unit 16, with the result that this yields a doubly faceted system, the fundamental principle of which is also referred to as a fly's eye integrator. If the second facet mirror 19like in the depicted exemplary embodimentis arranged in a pupil plane of the illumination optical unit 16, it is also referred to as a pupil facet mirror. However, the second facet mirror 19 may also be arranged at a distance from a pupil plane of the illumination optical unit 4, as a result of which a specular reflector arises from the combination of the first and the second facet mirror 18, 19, for example as described in US 2006/0132747 A1, EP 1 614 008 B1 and U.S. Pat. No. 6,573,978.

[0071] The second facet mirror 19, too, comprises a multiplicity of micromirrors 19 that are individually pivotable about two perpendicular axes in each case and are each equipped with a tilt sensor (not depicted here) for ascertaining the orientation of the micromirror 19. For further explanations, reference is made to DE 10 2008 009 600 A1.

[0072] The individual facets of the first facet mirror 18 are imaged into the object field 11 with the aid of the second facet mirror 19, with this regularly only being approximate imaging. The second facet mirror 19 is the last beam-shaping mirror or actually the last mirror for the illumination radiation in the beam path upstream of the object field 11.

[0073] In each case one of the facets of the second facet mirror 19 is assigned to exactly one of the facets of the first facet mirror 18 for the purpose of forming an illumination channel for illuminating the object field 11. This may in particular produce illumination according to the Khler principle.

[0074] The facets of the first facet mirror 18 are imaged overlaid on one another with a respective assigned facet of the second facet mirror 19, for the purposes of fully illuminating the object field 11. Here, the full illumination of the object field 11 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. The field uniformity can be achieved through the overlay of different illumination channels.

[0075] By selecting the ultimately used illumination channels, which is possible without problems with a suitable adjustment of the micromirrors 18, 19, it is still possible to adjust the intensity distribution in the entrance pupil of the projection system 20 described below. This intensity distribution is also referred to as illumination setting. Incidentally, it may be advantageous here to arrange the second facet mirror 19 not exactly in a plane that is optically conjugate to a pupil plane of the projection system 20. In particular, the pupil facet mirror 19 can be arranged so as to be tilted relative to a pupil plane of the projection system 20, as is described in DE 10 2017 220 586 A1, for example.

[0076] In the arrangement of the components of the illumination optical unit 16 shown in FIG. 1, however, the second facet mirror 19 is arranged in an area conjugate to the entrance pupil of the projection system 20. Reflection mirror 17 and the two facet mirrors 18, 19 are arranged tilted both vis--vis the object plane 12 and vis--vis one another in each case.

[0077] In an alternative embodiment (not depicted here) of the illumination optical unit 16, a transfer optical unit comprising one or more mirrors may additionally be provided in the beam path between the second facet mirror 19 and the object field 11. The transfer optical unit may in particular comprise one or two normal-incidence mirrors (NI mirrors) and/or one or two grazing-incidence mirrors (GI mirrors). Using an additional transfer optical unit, it is possible in particular to take account of different poses of the entrance pupil for the tangential and for the sagittal beam path of the projection system 20 described below.

[0078] Alternatively, the deflection mirror 17 depicted in FIG. 1 may be dispensed with, for which purpose then the facet mirrors 18, 19 should be suitably arranged vis--vis the radiation source 13 and the collector 14.

[0079] The object field 11 in the object plane 12 is transferred onto the image field 21 in the image plane 22 with the aid of the projection system 20.

[0080] To this end, the projection system 20 comprises a plurality of mirrors M.sub.i, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

[0081] In the example depicted in FIG. 1, the projection system 20 comprises six mirrors M.sub.1 to M.sub.6. Alternatives with four, eight, ten, twelve or any other number of mirrors M.sub.i are likewise possible. The penultimate mirror M.sub.5 and the last mirror M.sub.6 each have a passage opening for the illumination radiation, as a result of which the depicted projection system 20 is a doubly obscured optical unit. The projection system 20 has an image-side numerical aperture that is greater than 0.3 and may also be greater than 0.6, and may be for example 0.7 or 0.75.

[0082] The reflection surfaces of the mirrors M.sub.i may be in the form of freeform surfaces without an axis of rotational symmetry. However, the reflection surfaces of the mirrors M.sub.i can alternatively also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optical unit 16, the mirrors M.sub.i can have highly reflective coatings for the illumination radiation. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0083] The projection system 20 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 11 and a y-coordinate of the center of the image field 21. This object-image offset in the y-direction can be of approximately the same magnitude as a z-distance between the object plane 21 and the image plane 22.

[0084] In particular, the projection system 20 can be designed to be anamorphic, that is to say it has a different imaging scales .sub.x, .sub.y in the x- and y-directions in particular. The two imaging scales .sub.x, .sub.y of the projection system 20 are preferably (.sub.x, .sub.y)=(+/0.25,/+0.125). An imaging scale of 0.25 corresponds here to a reduction with a ratio of 4:1, while an imaging scale of 0.125 results in a reduction with a ratio of 8:1. A positive sign in the case of the imaging ratio means imaging without image inversion; a negative sign means imaging with image inversion.

[0085] Other imaging scales are likewise possible. Other imaging scales .sub.x, .sub.y with the same sign and the same absolute magnitude in the x- and y-directions are also possible.

[0086] The number of intermediate image planes in the x-direction and in the y-direction in the beam path between the object field 11 and the image field 21 can be the same or different, depending on the embodiment of the projection system 20. Examples of projection systems 20 with different numbers of such intermediate images in the x-direction and y-direction are known from US 2018/0074303 A1.

[0087] In particular, the projection system 20 can comprise a homocentric entrance pupil, which can be accessible or be inaccessible.

[0088] A mask 30 (also referred to as reticle) arranged in the object field 11 is exposed by the illumination system 10 and transferred by the projection system 20 onto the image plane 21. The mask 30 is held by a reticle holder 31. The reticle holder 31 is displaceable by a reticle displacement drive 32, in particular in a scanning direction.

[0089] A structure on the mask 30 is imaged onto a light-sensitive layer of a wafer 35 arranged in the region of the image field 21 in the image plane 22. The wafer 35 is held by a wafer holder 36. The wafer holder 36 is displaceable with a wafer displacement drive 37, in particular in the y-direction. The displacement on the one hand of the mask 30 with the reticle displacement drive 32 and on the other hand of the wafer 35 with the wafer displacement drive 37 may take place so as to be synchronized with one another.

[0090] The projection exposure apparatus 1 depicted in FIG. 1 or the illumination system 20 thereof, the above description of which substantially reflects the known prior art, is developed using an arrangement 100 according to the invention.

[0091] In principle, the arrangement 100 comprises a radiation source 101 that emits electromagnetic radiation, with the exposure radiation source 13 of the illumination system 10 being used as radiation source 101 in the exemplary embodiment depicted in FIG. 1, with the result that it is possible to dispense with a separately embodied radiation source.

[0092] Further, the arrangement comprises a radiation detector 102, which is stationarily arranged in the vicinity of the object plane 12 of the illumination system 10 so that a suitable adjustment of the micromirrors 18, 19 of the two facet mirrors 18, 19 of the illumination system 10 yields a beam path 103 from the radiation source 101 to the radiation detector 102, with in each case only one micromirror 18, 19 from each of the two facet mirrors 18, 19 affecting this beam path. The radiation detector 102 is an intensity detector which is provided with a bandpass filter (not depicted here) adapted to the wavelength of the beam source 101i.e., EUV in particular. Moreover, the radiation detector 102 is equipped with a stop 104 which is used to delimit the active area of the radiation detector 102.

[0093] The use of this arrangement 100 for system-integrated calibration of the facet mirrors 18, 19 of the illumination system 10and hence the method according to the inventionis now explained on the basis of FIGS. 2A-4.

[0094] FIGS. 2A and 3A each show a schematic portion of the illumination optical unit 16 of FIG. 1 which is relevant to the arrangement 100 and the use thereof, comprising the two facet mirrors 18, 19 (with individual micromirrors 18, 19 of the two facet mirrors 18, 19 being depicted in exemplary fashion) and the mask 30 located in the object plane 12. The radiation detector 102 of the arrangement 100 is also depicted. FIG. 4 schematically shows an exemplary procedure of a method according to the invention.

[0095] In principle, the micromirrors 18, 19 are suitably aligned for the exposure of the mask 30 in accordance with a desired intensity distribution, as is sufficiently well known from the prior art. However, one micromirror 18, 19 on each of the two facet mirrors 18, 19 is aligned deviating therefrom, such that this yields a beam path 103 from the radiation source 101 (cf. FIG. 1) to the radiation detector 103 via precisely these two micromirrors 18, 19. Since the remaining micromirrors 18, 19 are suitably aligned for exposure purposes, it is ensured that only this beam path 103 is in fact incident on the radiation detector 102.

[0096] Provision is made for the two micromirrors 18, 19 to be initially pivoted into the orientation required to establish the desired beam path 103 (cf. FIG. 4, step 200). To this end, it is possible to resort to the calibration of the micromirrors 18, 19 existing in principle, that is to say it is possible to set an angle specification for each of the two axes about which the micromirrors 18, 19 are pivotable, under monitoring by the tilt sensors of the micromirrors 18, 19. As a rule, despite a possible sensor drift of the tilt sensor, an existing calibration still is sufficiently accurate to be able to set up the beam path 103 as a matter of principle, and this can also be verified by determining radiation from the radiation source 101 being incident on the radiation detector 102. Should a corresponding verification fail, attempts should be made to methodically pivot, according to a given search pattern, the micromirrors 18, 19 affecting the envisaged beam path 103 until radiation emanating from the radiation source 101 can be determined by the radiation detector 102.

[0097] Proceeding from the initial orientation obtained by the initial pivoting of the two micromirrors 18, 19, one of the two micromirrors 18, 19 affecting the beam path 103 is methodically pivotedthis is the micromirror 18 in FIG. 2A and the micromirror 19 in FIG. 3A (cf. FIG. 4, step 210).

[0098] In this case, the micromirrors 18, 19 are each pivoted methodically over the entire pivot range in which the beam path 103 is incident on and detected by the radiation detector 102. In particular, the detection is no longer the case when pivoting the micromirror 18 if the part of the beam path 103 emanating from the micromirror 18 is no longer incident on the micromirror 19 (cf. FIG. 2A); in this case, the outline of the micromirror 19 acts like a stop for the beam path 103. Something comparable happens when pivoting the micromirror 19: The part of the beam path 103 emanating therefrom is incident on the stop 104 depending on the orientation of the micromirror 19 and can then no longer be detected by the radiation detector 102.

[0099] FIGS. 2B and 3B each plot the intensity I of the incident radiation detected by the radiation detector 102 against the pivot angle recorded by the tilt sensor of the respective methodically pivoted micromirror 18 (FIG. 2B) or 19 (FIG. 3B). In this case, the representation in FIGS. 2A-3B is restricted in each case to pivoting on a pivot axis of the micromirrors 18, 19 perpendicular to the plane of the sheet. If, as in the present case, the micromirrors 18, 19 are pivotable about two axes, the methodical pivoting should also be carried out over each of the axes, it being possible to consider the two axes simultaneously or successively with a temporal offset.

[0100] From the data recorded thus, it is possible to ascertain the optimal pivot position of the methodically pivoted micromirror 18 (FIG. 2B) or 19 (FIG. 3B) (cf. FIG. 4, step 220), for which optimal pivot position the part of the beam path 103 emanating from the micromirror 18 is incident as centrally as possible on the micromirror 19 or the part of the beam path 103 emanating from the micromirror 19 is incident as centrally as possible on the radiation detector 102: This is because the optimal pivot position corresponds to the central maximum of the intensity I.sub.max, med.

[0101] For the optimal pivot position I.sub.max, med ascertained thus, it is possible in each case to ascertain from the recorded data the associated pivot angle .sub.1 detected by the tilt sensor of the respective micromirror 18, 19 or the orientation of the methodically pivoted micromirror 18 or 19 ascertained by the respective tilt sensor (cf. FIG. 4, step 230).

[0102] On account of the precise knowledge of the arrangement of radiation source 101, the facet mirrors 18, 19 or the micromirrors 18, 19 and radiation detector 102, it is also possible to calculate that orientation of the methodically pivoted micromirror 18, 19 which should correspond to the optimal pivot position. This calculated orientation also yields the pivot angle * which the tilt sensor should have actually specified for the optimal pivot position of the methodically pivoted micromirror 18 or 19. .sub.y comparing the pivot angle .sub.1 detected by the tilt sensor for the optimal pivot position with the pivot angle * calculated for this pivot position (cf. FIG. 4, step 240), it is already possible as a matter of principle to adapt the calibration of the tilt sensor for this one pivot position on the basis of the comparison (cf. FIG. 4, step 250).

[0103] However, for a specific micromirror 18 or 19 to be pivoted methodically, provision is made for the above-described steps 200-240 to be carried out for a total of five different beam paths 103 (cf. FIG. 4, arrow 245). The five micromirrors 19 or 18 which are on the facet mirror 19, 18 that does not comprise the micromirror 18, 19 to be pivoted methodically but which each affect one of the five beam paths 103 are preferably arranged here in the form of a cross on the respective facet mirror 19, 18, that is to say three of the micromirrors 19, 18 are in each case located on a common straight line, with the respective middle micromirror 19, 18 thereof being located on both mutually perpendicular straight lines.

[0104] This yields a total of five of the above-described comparisons of detected and calculated orientations or pivot angles .sub.1, * for the respective optimal pivot positions of the micromirror 18 or 19 to be pivoted methodically, in each case for one beam path 103 (cf. FIG. 4, step 240), and these can be used to recalibrate the tilt sensor of the micromirror 18 or 19 (cf. FIG. 4, step 250).

[0105] This is helpful, in particular for tilt sensors which have a possibly non-linear, two-dimensional characteristic on account of pivotability about two separate axes since the five support points arising from the aforementioned five comparisons are generally enough to adapt the two-dimensional characteristic of the tilt sensor over the aforementioned pivot range, and thus achieve a complete recalibration of the tilt sensor. Depending on the characteristic of the tilt sensor or the required accuracy of the calibration, however, it is naturally also possible that significantly more beam paths and resultant comparisons are required to carry out a suitable calibration.

[0106] As is apparent from FIGS. 2A-3B, micromirrors 18, 19 of both the first and the second facet mirror 18, 19 can be calibrated by a defined pair of radiation source 101 and radiation detector 102. In this case, it is advantageous if the calibration of individual micromirrors 19 of the second facet mirror 19 is carried out only with the aid of micromirrors 18 of the first facet mirror 18 that were already previously calibrated in accordance with the invention. In other words, the micromirrors of the facet mirror 18 closer to the radiation source 103 along the radiation path 103 should be calibrated first.

[0107] FIGS. 5A and 5B depict alternative embodiments of the arrangement 100 according to FIGS. 1 to 3A. In this case, the illustration of FIGS. 5A and 5B is restricted to the relevant schematic portion of the illumination optical unit 16, already known from FIGS. 2A and 3A, of a projection exposure apparatus 1 according or comparable to FIG. 1.

[0108] The arrangements 100 according to FIGS. 5A and 5B are distinguished in that, instead of using the exposure radiation source 13 as a radiation source 101, provision is made of a separate radiation source 101 for the creation of the desired beam paths 103, this separate radiation source emitting light in the visible range. The radiation sources 101 in FIGS. 5A and 5B each comprise a high power light-emitting diode.

[0109] In FIG. 5A, the radiation source 101 is arranged in the vicinity of the intermediate focus of the exposure radiation source 13 of the illumination system 10, whereby the radiation detector 102 continues to remain arranged in the vicinity of the object plane 22. In the embodiment variant according to FIG. 5B, the positions of the radiation source 101 and of the radiation detector have been interchanged in comparison with FIG. 5A.

[0110] The calibration of the individual micromirrors 18, 19 of the facet mirrors 18, 19 of the illumination system 10 can be implemented in a manner analogous to the procedure described in the context of FIGS. 1 to 3A, and so reference is made to the explanations given there.

[0111] In order to avoid any conceivable interference with the actual exposure procedure by a calibration using a separate radiation source 101, the radiation source 101 is only used temporally decoupled from the exposure radiation source 13, that is to say the radiation source 101 only emits radiation when the exposure radiation source 13 does not emit radiation. Since the exposure radiation source 13 is regularly operated to emit high frequency pulses, the radiation source 101 can also be operated to emit high frequency pulses, and so in terms of the calibration procedure there is hardly any difference with a permanently operated radiation source 101.

[0112] Naturally, the provision of a plurality of radiation sources 101 and radiation detectors 102 is possible in order to be able to calibrate a plurality of micromirrors 18, 19 in parallelalso parallel in time with an exposure-resulting in less time being required for a complete calibration of all micromirrors 18, 19 from both facet mirrors 18, 19.