WO2013156251A1

WO2013156251A1 - Optical system of a microlithographic projection exposure apparatus, and method for adjusting an optical system

Info

Publication number: WO2013156251A1
Application number: PCT/EP2013/056079
Authority: WO
Inventors: Ingo SÄNGER; Michael Patra; Christoph HENNERKES; Bastian Trauter
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2012-04-16
Filing date: 2013-03-22
Publication date: 2013-10-24
Also published as: DE102012206148A1

Abstract

The invention relates to an optical system of a microlithographic projection exposure apparatus, and to a method for adjusting an optical system. An optical system comprises a mirror arrangement (120, 200, 400, 500, 800, 900) having a plurality of mirror elements (120a, 120b, 120c,... ) which are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement, a polarization-influencing optical arrangement (110) having at least one polarization-influencing component (111, 112, 113, 310, 320, 411, 511), wherein, by displacing said polarization-influencing component, a degree of overlap between the polarization-influencing component and the mirror arrangement can be set in a variable manner, and a light coupling-out region (630, 730, 830, 930), which, for the purpose of taking account of a possible incorrect positioning of the polarization-influencing component, couples out light from the beam path of the optical system in such a way that no light passes into a pupil plane of the projection exposure apparatus from a partial region of the mirror arrangement during the operation of the optical system.

Description

Optical system of a microlithographic projection exposure apparatus,

and method for adjusting an optical system

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Application DE 10 2012 206 148.7 and US 61/624,434, both filed on April 16, 2012. The content of these applications is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an optical system of a microlithographic projection exposure apparatus, and to a method for adjusting an optical system.

Prior Art

Microlithography is used for producing microstructured components, such as, for example, integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus comprising an illumination device and a projection lens. In this case, the image of a mask (= reticle) illuminated by means of the illumination device is projected, by means of the projection lens, onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.

During the operation of a microlithographic projection exposure apparatus there is a need to set defined illumination settings, i.e. intensity distributions in a pupil plane of the illumination device, in a targeted manner. For this purpose, besides the use of diffractive optical elements (so-called DOEs), the use of mirror arrangements is also known, e.g. from WO 2005/026843 A2. Such mirror arrangements comprise a multiplicity of micromirrors that can be set independently of one another.

Furthermore, various approaches are known for setting, in the illumination device, for the purpose of optimizing the imaging contrast, specific polarization distributions in the pupil plane and/or in the reticle in a targeted manner. In particular, it is known, both in the illumination device and in the projection lens, to set a tangential polarization distribution for high-contrast imaging. "Tangential polarization" (or "TE polarization") is understood to mean a polarization distribution in which the planes of vibration of the electric field strength vectors of the individual linearly polarized light rays are oriented approximately perpendicularly to the radius directed toward the optical system axis. By contrast, "radial polarization" or ("TM polarization") is understood to mean a polarization distribution in which the planes of vibration of the electric field strength vectors of the individual linearly polarized light rays are oriented approximately radially with respect to the optical system axis.

With regard to the prior art, reference is made for example to WO 2005/069081 A2, WO 2005/031467 A2, US 6, 191 ,880 B1 , US 2007/0146676 A1 , WO 2009/034109 A2, WO 2008/019936 A2, WO 2009/100862 A1 , DE 10 2008 009 601 A1 , DE 10 2004 01 1 733 A1 and US 201 1 /0228247 A1 .

One possible approach for flexibly setting the polarization distribution in this case comprises the use of a polarization-influencing optical arrangement composed of a plurality of polarization-influencing components arranged such that they are displaceable transversely with respect to the light propagation direction in combination with a mirror arrangement comprising a multiplicity of mirror elements that are adjustable independently of one another. In this case, depending on the degree of coverage of the mirror arrangement by the polarization-influencing components in conjunction with a likewise variable setting of the mirror elements of the mirror arrangement, it is possible to realize different polarization distributions in the pupil plane of the illumination device in a flexible manner.

In the case of this approach, however, the problem can occur in practice that, in the case of inexact positioning of the polarization-influencing components, e.g. as a result of the unintentional partial or complete coverage of one or more mirror elements by one or more polarization-influencing components of the polarization- influencing arrangement, an incorrect polarization state is applied to portions of the light reflected into the pupil plane by the mirror arrangement, such that the polarization distribution obtained in the pupil plane deviates from the desired polarization distribution. As a result, this can lead to an impairment of the performance of the projection exposure apparatus on account of imaging aberrations and loss of contrast.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical system of a microlithographic projection exposure apparatus and a method for adjusting an optical system which make possible a flexible setting of different polarization distributions with higher accuracy and whilst avoiding imaging aberrations induced thereby.

This object is achieved in accordance with the features of the independent claims.

An optical system according to the invention of a microlithographic projection exposure apparatus comprises:

- a mirror arrangement having a plurality of mirror elements which are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement;

- a polarization-influencing optical arrangement having at least one polarization- influencing component, wherein, by displacing said polarization-influencing component, a degree of overlap between the polarization-influencing component and the mirror arrangement can be set in a variable manner; and

- a light coupling-out region, which, for the purpose of taking account of a possible incorrect positioning of the polarization-influencing component, couples out light from the beam path of the optical system in such a way that no light passes into a pupil plane of the projection exposure apparatus from a partial region of the mirror arrangement during the operation of the optical system. The invention is based on the concept, in particular, of providing, in the polarization- influencing optical arrangement, at least one component with a region which is a light coupling-out (as it were "non-transmissive") region in so far as light incident on this edge region does not reach the reticle plane or wafer plane. What can thereby be achieved is that portions of the light incident on the polarization-influencing optical arrangement with an incorrect orientation of the polarization direction, on account of said light coupling-out region, do not participate in the imaging and can be ignored. Given correspondingly accurate manufacture of the light coupling-out region, after the polarization-influencing optical arrangement has been incorporated into the illumination device, under certain circumstances, further adjustment steps are no longer required. Moreover, in a further aspect, as will be explained in even greater detail, an adjustment of the components of the polarization-influencing optical arrangement can be carried out by virtue of the fact that use can advantageously be made of the light coupling-out or non-transmissive region. In accordance with one embodiment, the light coupling-out region is provided on the polarization-influencing component, in particular in an edge region of the polarization- influencing component.

In accordance with one embodiment, the light coupling-out region has a reflective and/or absorbent coating provided on the polarization-influencing component, in particular a chromium (Cr) coating. In accordance with one embodiment, the light coupling-out region has a chamfer provided at the polarization-influencing component.

In accordance with one embodiment, the polarization-influencing component has a beveled edge for preventing light from entering laterally into the component.

In accordance with one embodiment, the light coupling-out region has a width which is in the range of 5% to 95% of the width of a mirror element of the mirror arrangement.

In accordance with a further aspect, the invention relates to a method for adjusting an optical system of a microlithographic projection exposure apparatus, wherein the optical system comprises a mirror arrangement having a plurality of mirror elements which are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement, and a polarization-influencing optical arrangement having at least one polarization- influencing component, wherein, by displacing said polarization-influencing component, a degree of overlap between the polarization-influencing component and the mirror arrangement can be set in a variable manner; wherein the method comprises the following steps:

- positioning a light coupling-out region in the optical system in such a way that no light passes into a pupil plane of the projection exposure apparatus from a partial region of the mirror arrangement during the operation of the optical system; - carrying out an intensity measurement for light incident in the pupil plane after reflection at mirror elements of the mirror arrangement; and

- determining a change in position of the polarization-influencing component, said change being required for generating a desired polarization distribution, on the basis of the intensity measurement carried out.

In accordance with one embodiment, the light coupling-out region is provided on the polarization-influencing component, in particular in an edge region of the polarization- influencing component.

In accordance with one embodiment, when carrying out the intensity measurement, mirror elements which are at a distance from the light coupling-out region that exceeds a predefined threshold value are disregarded. Said threshold value can correspond, for example, to the width of a mirror element of the mirror arrangement, or to an integral multiple of said width. In accordance with one embodiment, when carrying out the intensity measurement, mirror elements which have a degree of overlap with the polarization-influencing component that is 100% or zero are disregarded.

In accordance with one embodiment, light reflected at the disregarded mirror elements is deflected into a separate region of the pupil plane or toward a ray trap.

Further configurations of the invention can be gathered from the following description and from the dependent claims. The invention is explained in greater detail below on the basis of preferred exemplary embodiments and with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

Figure 1 shows a schematic illustration of the construction of a microlithographic projection exposure apparatus on which the present invention can be realized; Figures 2-3 show schematic illustrations for elucidating possible embodiments for flexibly setting different polarization states; and

Figures 4-9 show schematic illustrations for elucidating a concept according to the invention for calibrating or adjusting a polarization-influencing optical arrangement used in the exemplary embodiments from Figure 2 or Figure 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, a basic construction of a microlithographic projection exposure apparatus comprising an optical system according to the invention will firstly be explained with reference to Fig. 1 . The projection exposure apparatus comprises an illumination device 10 and a projection lens 20. The illumination device 10 serves for illuminating a structure-bearing mask (reticle) 30 with light from a light source unit 1 , which comprises, for example, an ArF excimer laser for an operating wavelength of 193 nm and a beam shaping optical unit, which generates a parallel light beam. Generally, the illumination device 10 and the projection lens 20 are preferably designed for an operating wavelength of less than 400 nm, in particular less than 250 nm, furthermore in particular less than 200 nm.

According to the invention, part of the illumination device 10 is, in particular, a mirror arrangement 120 having a multiplicity of mirror elements which can be set independently of one another. A polarization-influencing optical arrangement 1 10, which will be explained in even greater detail below with reference to Fig. 2 et seq., is arranged upstream of the mirror arrangement 120 in the light propagation direction. In accordance with Fig. 1 , driving units 1 15, 125 are furthermore provided, which are assigned to the polarization-influencing optical arrangement 1 10 and to the mirror arrangement 120, respectively, and respectively enable said arrangements to be adjusted by means of suitable actuators. Actuators for adjusting the arrangements can be configured in any desired manner, e.g. as belt drives, flexure elements, piezo- actuators, linear drives, direct-current (DC) motors with or without a gear mechanism, spindle drives, toothed belt drives, gearwheel drives or combinations of these known components. The illumination device 10 has an optical unit 1 1 , which comprises a deflection mirror 12 inter alia in the example illustrated. Downstream of the optical unit 1 1 in the light propagation direction there are situated in the beam path a light mixing device (not illustrated), which can have e.g., in a manner known per se, an arrangement of micro-optical elements suitable for achieving light mixing, and a lens element group 14, downstream of which is situated a field plane with a reticle masking system (REMA), which is imaged, by a REMA lens 15 disposed downstream in the light propagation direction, onto the structure-bearing mask (reticle) 30 arranged in a further field plane and thereby delimits the illuminated region on the reticle. The structure-bearing mask 30 is imaged by the projection lens 20 onto a substrate 40, or a wafer, provided with a light-sensitive layer. The projection lens 20 can be designed, in particular, for immersion operation. Furthermore, it can have a numerical aperture NA of greater than 0.85, in particular greater than 1 .1 .

The mirror arrangement 120 (also designated as "MMA", MMA = "micro mirror array") has, in accordance with Fig. 2, a plurality of mirror elements 120a, 120b, 120c, ... . The mirror elements 120a, 120b, 120c, ... are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement 120, the driving unit 125 serving for this purpose in accordance with Fig. 1 . Upstream of the mirror arrangement 120 in the light propagation direction, in the exemplary embodiment, there is also situated a microlens element arrangement 105, which is not shown in Fig. 1 but is indicated schematically in Fig. 2 and which has a multiplicity of microlens elements for targeted focusing onto the mirror elements of the mirror arrangement in order to avoid loss of light and generation of stray light in the regions between the individual mirrors (as a result of spillover radiation of the individual mirrors). The mirror elements 120a, 120b,

120c, ... can each be tilted individually, e.g. in an angular range of -2° to +2°, in particular -5° to +5°, furthermore in particular -10° to +10°. By means of a suitable tilting arrangement of the mirror elements 120a, 120b, 120c, ... in the mirror arrangement 120, a desired light distribution, e.g. an annular illumination setting or else a dipole setting or a quadripole setting, can be formed in the pupil plane PP by virtue of the previously homogenized and collimated laser light in each case being directed in the corresponding direction depending on the desired illumination setting by means of the mirror elements 120a, 120b, 120c, ... .

Fig. 2 initially serves for elucidating the interaction of the polarization-influencing optical arrangement 1 10, already mentioned in connection with Fig. 1 , with the mirror arrangement 120.

In the exemplary embodiment in Fig. 2, the polarization-influencing optical arrangement 1 10 has three components in the form of optical rotators 1 1 1 -1 13 composed of optically active crystalline quartz, which components are adjustable independently of one another and can be introduced into the beam path in each case perpendicularly to the light propagation direction, wherein each of said rotators, for light passing through, brings about by itself a rotation of the preferred direction of polarization by 45°. Consequently, the preferred direction of polarization is rotated by 45° upon light passing through only one rotator 1 1 1 , 1 12 or 1 13, by 90° when light passes through two of said rotators 1 1 1 -1 13, and by 135° (or -45°) when light passes through all the rotators 1 1 1 -1 13. This situation is illustrated in Fig. 2, wherein the double-headed arrows depicted for the partial beams S1 -S4 in each case denote the preferred direction of polarization as seen in the z-direction (when viewed in the x-y plane). In this case, the partial beam S1 does not pass through any of the rotators 1 1 1 -1 13, and so the preferred direction of polarization (which corresponds to the x- direction in the example) remains unchanged for this partial beam.

The microlens element arrangement 105 is likewise illustrated only schematically in Fig. 2, said arrangement, as mentioned above, focusing the individual partial beams respectively onto mirror elements 120a, 120b, 120c, 120d, ... of the mirror arrangement 120. The positioning of said microlens element arrangement 105 is merely by way of example, in which case, in further exemplary embodiments, the microlens element arrangement 105 can also be arranged after the polarization- influencing optical arrangement 1 10 or downstream thereof in the light propagation direction. Depending on the degree of coverage of the mirror arrangement 120 by the polarization-influencing components 1 1 1 , 1 12, 1 13 in conjunction with the variable setting of the mirror elements 120a, 120b, 120c, ... of the mirror arrangement 120, different polarization distributions in the pupil plane of the illumination device can be realized in a flexible manner with the construction from Fig. 2.

Fig. 3a shows the polarization-influencing optical arrangement 300 in accordance with a further embodiment of the invention in schematic illustration. In accordance with Fig. 3a, the polarization-influencing optical arrangement 300 comprises lambda/2 plates 310, 320 partly overlapping one another, which are in each case produced from a suitable birefringent material having sufficient transparency at the desired operating wavelength, for example from magnesium fluoride (MgF₂), sapphire (AI₂Os) or crystalline quartz (Si0₂). Furthermore, the lambda/2 plates 310, 320 (without the invention being restricted to this) each have a rectangular geometry in adaptation to the geometry of the mirror arrangement 200.

Fig. 3a likewise depicts, for the case of the incidence of linearly polarized light having a constant preferred direction of polarization P running in the y-direction, the preferred directions of polarization respectively arising after light passes through the polarization-influencing optical arrangement 300. In this case, the respectively arising preferred direction of polarization is designated by P' for the first non-overlap region

"Β- (i.e. the region covered only by the first lambda/2 plate 310), by P" for the second non-overlap region "B-2" (i.e. the region covered only by the second lambda/2 plate 320), and by P'" for the overlap region "A" (i.e. the region covered both by the first lambda/2 plate 310 and by the second lambda/2 plate 320). The arising of the respective preferred directions of polarization in the abovementioned regions is illustrated schematically in Fig. 3b-e, wherein the respective position of the fast axis of birefringence (which runs in the direction of high refractive index) is indicated by the dashed line "fa-1" for the first lambda/2 plate 310 and by the dashed line "fa-2" for the second lambda/2 plate 320. In the exemplary embodiment, the fast axis "fa-1 " of birefringence of the first lambda/2 plate 310 runs at an angle of 22.5°+ 2° with respect to the preferred direction of polarization P of the light beam incident on the arrangement 300 (i.e. with respect to the y-direction), and the fast axis "fa-2" of birefringence of the second lambda/2 plate 320 runs at an angle of -22.5°+ 2° with respect to the preferred direction of polarization P of the light beam incident on the arrangement 300. The preferred direction of polarization P' arising after light passes through the first lambda/2 plate 310 corresponds to a mirroring of the original (input) preferred direction of polarization P at the fast axis "fa-1" (cf. Fig. 3b), and the preferred direction of polarization P" arising after light passes through the second lambda/2 plate 320 corresponds to a mirroring of the original (input) preferred direction of polarization P at the fast axis "fa-2" (cf. Fig. 3c). The preferred directions of polarization P' and P" arising after light passes through the non-overlap regions "B-1 " and "B-2", respectively, consequently run at an angle of + 45° with respect to the preferred direction of polarization P of the light beam incident on the arrangement 300. For the light beam incident on the arrangement 300 in the overlap region "A" it holds true that the preferred direction of polarization P' of the light beam emerging from the first lambda/2 plate 310 (cf. Fig. 3d) corresponds to the input polarization distribution of the light beam incident on the second lambda/2 plate 320, such that the preferred direction of polarization - designated by P'" in Fig. 3e - of the light beam emerging from the overlap region "A" runs at an angle of 90° with respect to the preferred direction of polarization P of the light beam incident on the arrangement

300.

Hereinafter, with reference to Fig. 4, firstly a description will be given of a problem which occurs in practice in the case of the above-described approaches for flexible polarization setting and which is dealt with by the present invention. Fig. 4 firstly shows once again the positioning of a polarization-influencing component 41 1 of a polarization-influencing optical arrangement 410 upstream of a mirror arrangement 400 in the light propagation direction. Said component 41 1 can be, for example, one of the rotators 1 1 1 , 1 12, 1 13 of the polarization-influencing optical arrangement 1 10 from Fig. 2 or else one of the lambda/2 plates 310, 320 from Fig. 3.

In this case, Fig. 4 is based on a situation in which the component 41 1 is not positioned exactly with respect to the mirror arrangement 400, that is to say that there is a deviation of the actual position of the component 41 1 relative to the desired position thereof. As illustrated in Fig. 4, this deviation of the actual position from the desired position has the effect that in a region (designated by "X" and illustrated in a hatched manner in Fig. 4) "incorrect" polarization states of the light passing through the component 41 1 are set, which in turn results in an undesirable reduction of the IPS value characterizing the degree of realization of the desired polarization state.

Hereinafter, it is assumed, then, that a correction of the incorrect positioning of the relevant component of the polarization-influencing optical arrangement as shown in Fig. 4 is either not possible or not desired.

Fig. 5 serves to illustrate the principle according to the invention. While an exact positioning of the polarization-influencing component 51 1 and thus an exact polarization setting would be possible without mechanical tolerances (cf. Fig. 5a), there exist owing to the tolerances present (e.g. a rotation about the z-axis (Rz) or a displacement along the y-axis) partial regions on individual mirror elements of the mirror arrangement 500 which are undesirably covered or undesirably not covered by the polarization-influencing component 51 1 (cf. Fig. 5b), which leads to a deviation from the desired polarization distribution and thus to an IPS loss. Depending on the magnitude of the mechanical tolerances, according to the invention, then, an edge region of the polarization-influencing component is processed such that said edge region has no transmission in the optical system in the sense that light is coupled out from the beam path of the optical system in so far as no light passes into the pupil plane of the illumination device from a partial region of the mirror arrangement or light does not even reach said partial region in the first place. In this case, the size of the corresponding light coupling-out region 530 is chosen such that, taking account of the tolerances, the mirror elements or mirror element regions (to which, without the abovementioned coupling-out, an "incorrect" or undesired polarization state is applied) are covered (cf. Fig. 5c). If a measurement of the position of the polarization-influencing component and a subsequent correction are possible, an uncertainty in the positioning accuracy of the polarization-influencing component which is to be covered by the light coupling-out region arises in this case, too, that is to say that a residual misorientation that nevertheless remains is preferably covered by the extent of the polarization-influencing component.

The present invention is therefore based on the concept of "blocking" light polarized "incorrectly" owing to a possible or expected incorrect position of the component of the polarization-influencing optical arrangement in such a way that said light no longer participates in the further imaging beam path, that is to say does not reach the reticle or the wafer. In this case, the dimensioning of the region that is correspondingly to be blocked is chosen depending on the mechanical tolerances present, i.e. depending on how accurately the relevant component of the polarization- influencing optical arrangement can be positioned initially (i.e. e.g. without further adjustment).

In other words, for the case where the incorrect positioning of the component of the polarization-influencing optical arrangement can be comparatively great in the concrete design of the system, the geometrical extent of the blocking or light coupling-out region is chosen to be of a corresponding size, whereas for the case of a comparatively accurate positionability of the polarization-influencing component, the corresponding blocking or light coupling-out region can be designed to be relatively narrow. The light coupling-out region provided according to the invention is preferably provided directly on the relevant component of the polarization-influencing optical arrangement, in respect of which embodiments are described below with reference to Fig. 6 and 7.

In accordance with Fig. 6, the light is blocked in the relevant region 630 by means of a coating which at least partly absorbs and/or reflects incident light, said coating being realized as a chromium coating (having a thickness, merely by way of example, of the order of magnitude of 100 nm) in the exemplary embodiment. As can likewise be seen from Fig. 6, in addition to said chromium coating, the relevant component of the polarization-influencing optical arrangement has a beveled (at an angle β) edge, which is optional, in principle, and in the exemplary embodiment is intended to prevent light rays that emerge from the mirror arrangement obliquely from being incident on the component laterally (e.g. from the top right in Fig. 6) and generating undesirable stray light in this way.

Fig. 7 shows a further exemplary embodiment, in which the component of the polarization-influencing optical arrangement is provided with a chamfer or beveled surface. As is illustrated schematically in Fig. 7, the light incident in the direction of the arrow "P" is either reflected at the chamfer in the direction of the arrow "ΡΓ or

(according to Snell's law of refraction) refracted in the direction of the arrow "P2". In both cases (i.e. both in the case of reflection and in the case of refraction of the light), the light is directed out of the imaging beam path, such that it does not reach the reticle or wafer. Consequently, said chamfer, too, forms a light coupling-out or non- transmissive region for the light incident on the component.

In further embodiments, the light coupling-out region to be provided according to the invention on at least one component of the polarization-influencing optical arrangement can also be realized in some other way, for example in the form of a corresponding roughening of the surface of the component, wherein light incident on the roughened region is scattered in such a way that stray light generated no longer participates in the further imaging beam path. Merely by way of example, the dimensioning of the arrangements shown in Fig. 6 and 7, respectively, can be provided such that, given dimensions of the mirror elements of the mirror arrangement of 1 mm*1 mm, a width of the light coupling-out region can be e.g. in the range of 100 μηι to 800 μηι. In accordance with a further criterion, the width of the light coupling-out region (e.g. of the coating 630 in Fig. 6 or of the chamfer 730 in Fig. 7) can be in the range of 5% to 95% of the width of the mirror elements of the mirror arrangement. Here, the width - designated in each case by "b1 " in Fig. 6 and 7 - of the light coupling-out region can be chosen suitably in each case, as already mentioned, depending on the tolerances during the positioning of the components of the polarization-influencing optical arrangement.

Given correspondingly accurate manufacture of the light coupling-out region, after the polarization-influencing optical arrangement has been incorporated into the illumination device, under certain circumstances, further adjustment steps are no longer required. In this case, portions of the light incident on the polarization- influencing optical arrangement with a misorientation of the polarization direction can then be ignored in so far as they do not participate in the imaging on account of said light coupling-out region.

In a further configuration of the invention, in addition to - as described above - taking account of or eliminating mechanical tolerances, during the positioning of the polarization-influencing component, an adjustment of the components of the polarization-influencing optical arrangement can also be carried out, in which case use can now advantageously be made of the light coupling-out or non-transmissive region described above. This takes account of the circumstance that owing to a transmittance of the order of magnitude of 99.9% that is typically afforded in the case of the components of the polarization-influencing optical arrangement, a transmission measurement is not suitable straightforwardly or directly at the components of the polarization-influencing optical arrangement for adjustment purposes. However, since the light coupling-out region provided in accordance with Fig. 6 and 7 results, in an intensity measurement, in a decrease in the intensity to zero, with the aid of this region it is possible to effect a comparatively exact determination of the position of the light coupling-out region and thus also a determination of the edge of the polarization-influencing component of the polarization-influencing optical arrangement by means of a transmission or intensity measurement.

Consequently, the adjustment concept according to the invention makes use of the circumstance that the light coupling-out region embodied as above is directly discernible in a transmission measurement with the positioning of the corresponding component of the polarization-influencing optical arrangement in the beam path. Consequently, a transmission or intensity measurement can be carried out in the context of the present invention, for which purpose the light coupling-out or non- transmissive region is arranged in the beam path of the optical system.

Hereinafter, a corresponding adjustment concept according to the invention is described with reference to Fig. 7 and Fig. 8.

During this adjustment, with reference to Fig. 8a, the light coupling-out region 830, highlighted in a hatched manner, is intended to be displaced in the y-direction in the coordinate system depicted in such a way that it is positioned centrally at the boundary between two adjacent columns (columns 20 and 21 in Fig. 8a) of mirror elements of the mirror arrangement 800. Furthermore, the corresponding columns 20 and 21 situated in the region of the light coupling-out region 830 are directed into the pupil plane (illustrated in Fig. 8b) in such a way that the corresponding light spots generated in the pupil plane are present in the same arrangement as the associated mirror elements of the two columns 20 and 21 of the mirror arrangement 800. By contrast, the mirror elements (which are either not covered at all or covered completely by the component 81 1 of the polarization-influencing optical arrangement) of the columns 19, 22, etc. can be disregarded during the calibration and be directed e.g. into an outer marginal region of the pupil plane or to a ray trap arranged outside the imaging beam path. In other words, during the calibration according to the invention, firstly an individual light spot is generated in the pupil plane by means of each mirror element situated in the region of the light coupling-out region 830 of the corresponding component 81 1 to be adjusted of the polarization-influencing optical arrangement.

In accordance with Fig. 8b, in this case the light spots generated by those mirror elements of the column 20 of the mirror arrangement which are covered by the component 81 1 of the polarization-influencing optical arrangement are situated to the left of the hatched line depicted in the pupil plane, whereas the light spots generated by those mirror elements of the column 21 of the mirror arrangement which are not covered by the component 81 1 of the polarization-influencing optical arrangement are arranged at the right of the hatched line in the pupil plane.

The next step then involves, as indicated in Fig. 8b, integrating the intensities of said light spots both for the light spots generated by the mirror elements of the column 20 of the mirror arrangement 800 and for the light spots generated by the mirror elements of the column 21 of the mirror arrangement 800, which respectively produces a data point in the diagram shown in Fig. 8b. The next step then involves displacing the component 81 1 of the polarization- influencing optical arrangement in the y-direction over the mirror arrangement by a predetermined distance interval (e.g. Ay = 5 μηι). If this displacement is effected toward the left (i.e. in the positive y-direction) in Fig. 8a, then in the case of a subsequent analogous integration of the intensities obtained for the mirror elements of the column 21 of the mirror arrangement, the total intensity becomes lower if the light coupling-out region in this case becomes situated above the corresponding mirror elements of the column 21 to a greater extent, whereas the intensity value correspondingly obtained by integration for the mirror elements situated in the column 20 of the mirror arrangement 800 decreases.

Step-by-step further displacement of the component 81 1 of the polarization- influencing optical arrangement across the mirror arrangement finally leads to the obtaining of the entire diagram illustrated in Fig. 8b. The ideal edge position of the component 81 1 of the polarization-influencing optical arrangement can now be assumed for that y-position of the component 81 1 or the edge thereof at which the two curves "A" and "B" cross one another in the diagram in Fig. 8b, since then the light coupling-out region 830 is positioned exactly centrally above the columns 20, 21 of the mirror arrangement.

In addition to the above-described positioning of the component 81 1 of the polarization-influencing optical arrangement or the light coupling-out region 830 thereof in the y-direction, a further step then involves defining the Rz orientation, i.e. arranging the component 81 1 in such a way that the latter is not undesirably rotated about the z-axis (in the degree of freedom Rz). This step will now be described hereinafter with reference to Fig. 9. In this case, it is firstly assumed that with respect to the degree of freedom of the displacement in the y-direction, as described above, the optimum position of the component 81 1 of the polarization-influencing optical arrangement has been found and set.

For the purpose of measuring or optimizing the Rz orientation, in accordance with Fig. 9, firstly once again by means of each individual mirror element of the mirror arrangement 900 an individual separate illumination spot is then generated in the pupil plane for the mirror elements situated in the region of the light coupling-out region 930 of the component 91 1 and the associated intensity for the individual light spots is measured. In contrast to the procedure described with reference to Fig. 8, however, now the intensities thus determined are not integrated, rather the intensities of the individual light spots are plotted directly in a diagram (as illustrated in Fig. 9b).

A consideration of the profile in said diagram in accordance with Fig. 9a shows for the mirror elements of the column 21 of the mirror arrangement 900 a linear decrease in the intensity with increasing "projection" of the light coupling-out region 930 of the component 91 1 of the polarization-influencing optical arrangement, whereas a linear increase in the intensity correspondingly arises for the mirror elements of the column 20 of the mirror arrangement 900 that is covered (by the components 91 1 of the polarization-influencing optical arrangement).

According to the invention, the angle by which the component of the polarization- influencing optical arrangement is rotated (with respect to the degree of freedom Rz) is now calculated from the gradient of the straight lines shown in the diagram in Fig. 9c. In this case, given a known width of the individual mirror elements, that angle by which the component 91 1 of the polarization-influencing optical arrangement is rotated about the z-axis is calculated from said gradient of the straight lines. For the corresponding rotation about the z-axis, Rz=arctan(m) holds true, where m denotes said straight-line gradient.

Consequently, in accordance with Fig. 9b, already from a respective single intensity measurement for the light spots respectively generated in the pupil plane by means of the mirror elements of the columns 20, 21 of the mirror arrangement 900, the required angle of rotation is determined by which the component 91 1 of the polarization-influencing optical arrangement has to be rotated about the z-axis in order finally to position said component 91 1 exactly parallel to the transition region between the columns 20, 21 of the mirror arrangement 900.

Even though the invention has been described on the basis of specific embodiments, numerous variations and alternative embodiments are evident to the person skilled in the art, e.g. by combination and/or exchange of features of individual embodiments. Accordingly, it goes without saying for the person skilled in the art that such variations and alternative embodiments are concomitantly encompassed by the present invention, and the scope of the invention is restricted only within the meaning of the accompanying patent claims and the equivalents thereof.

Claims

1. Optical system of a microlithographic projection exposure apparatus, comprising:

• a mirror arrangement (120, 200, 400, 500, 800, 900) having a plurality of mirror elements (120a, 120b, 120c,...) which are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement (120, 200, 400, 500, 800, 900);

• a polarization-influencing optical arrangement (110) having at least one polarization-influencing component (111 , 112, 113, 310, 320, 411, 511), wherein, by displacing said polarization-influencing component, a degree of overlap between the polarization-influencing component (111, 112, 113, 310, 320, 411, 511, 611, 711, 811, 911) and the mirror arrangement (120, 200, 400, 500, 800, 900) can be set in a variable manner; and

• a light coupling-out region (630, 730, 830, 930), which, for the purpose of taking account of a possible incorrect positioning of the polarization- influencing component (111, 112, 113, 310, 320, 411, 511, 611, 711, 811, 911), couples out light from the beam path of the optical system in such a way that no light passes into a pupil plane of the projection exposure apparatus from a partial region of the mirror arrangement (120, 200, 400, 500) during the operation of the optical system.

2. Optical system according to Claim 1 , characterized in that the light coupling- out region (630, 730, 830, 930) is provided on the polarization-influencing component (111, 112, 113, 310, 320, 411, 511, 611, 711, 811, 911), in particular in an edge region of the polarization-influencing component (111, 112, 113, 310, 320, 411, 511, 611, 711 , 811 , 911 ).

3. Optical system according to Claim 1 or 2, characterized in that the light coupling-out region (630) has a reflective and/or absorbent coating provided on the polarization-influencing component (61 1 ), in particular a chromium (Cr) coating.

4. Optical system according to any of Claims 1 to 3, characterized in that the light coupling-out region (730) has a chamfer provided at the polarization- influencing component (71 1 ).

5. Optical system according to any of the preceding claims, characterized in that the polarization-influencing component (61 1 ) has a beveled edge for preventing light from entering laterally into the component (61 1 ).

6. Optical system according to any of the preceding claims, characterized in that the light coupling-out region has a width which is in the range of 5% to 95% of the width of a mirror element of the mirror arrangement.

7. Method for adjusting an optical system of a microlithographic projection exposure apparatus, wherein the optical system comprises:

• a mirror arrangement (120, 200, 400, 500, 800, 900) having a plurality of mirror elements (120a, 120b, 120c, ... ) which are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement (120, 200, 400, 500, 800, 900); and

• a polarization-influencing optical arrangement (1 10) having at least one polarization-influencing component (1 1 1 , 1 12, 1 13, 310, 320, 41 1 , 51 1 , 61 1 , 71 1 , 81 1 , 91 1 ), wherein, by displacing said polarization-influencing component, a degree of overlap between the polarization-influencing component (1 1 1 , 1 12, 1 13, 310, 320, 41 1 , 51 1 , 61 1 , 71 1 , 81 1 , 91 1 ) and the mirror arrangement (120, 200, 400, 500, 800, 900) can be set in a variable manner; wherein the method comprises the following steps: a) positioning a light coupling-out region (630, 730, 830, 930) in the optical system in such a way that no light passes into a pupil plane of the projection exposure apparatus from a partial region of the mirror arrangement (120, 200, 400, 500, 800, 900) during the operation of the optical system; b) carrying out an intensity measurement for light incident in the pupil plane after reflection at mirror elements of the mirror arrangement (120, 200, 400, 500, 800, 900); and c) determining a change in position of the polarization-influencing component (111, 112, 113, 310, 320, 411, 511, 611, 711, 811, 911), said change being required for generating a desired polarization distribution, on the basis of the intensity measurement carried out in step b).

Method according to Claim 7, characterized in that the light coupling-out region is provided on the polarization-influencing component (111, 112, 113, 310, 320, 411, 511), in particular in an edge region of the polarization- influencing component (111, 112, 113, 310, 320, 411, 511).

Method according to Claim 7 or 8, characterized in that, when carrying out the intensity measurement in step b), mirror elements which are at a distance from the light coupling-out region (630, 730, 830, 930) that exceeds a predefined threshold value are disregarded.

Method according to any of Claims 7 to 9, characterized in that, when carrying out the intensity measurement in step b), mirror elements which have a degree of overlap with the polarization-influencing component (111, 112, 113, 310, 320, 411, 511, 611, 711, 811, 911) that is 100% or zero are disregarded.

11. Method according to Claim 9 or 10, characterized in that light reflected at these disregarded mirror elements is deflected into a separate region of the pupil plane or toward a ray trap.