WO2014023619A1

WO2014023619A1 - Microlithographic exposure method, and microlithographic projection exposure apparatus

Info

Publication number: WO2014023619A1
Application number: PCT/EP2013/066041
Authority: WO
Inventors: Michael Patra
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2012-08-08
Filing date: 2013-07-30
Publication date: 2014-02-13
Also published as: DE102012214052A1

Abstract

The invention relates to a microlithographic exposure method, wherein at least one mirror arrangement (120) having a plurality of mirror elements (120a, 120b, 120c,...), which are adjustable independently of one another for varying an angular distribution of the light reflected by the mirror arrangement, and a polarization-influencing optical arrangement (110, 500, 600, 700, 800) are used in the illumination device (10), wherein the method comprises the following steps: determining, for a predefined desired distribution of the intensity and of the polarization state in a pupil plane of the illumination device, a desired distribution of the Stokes vector (S) in said pupil plane; determining, for a current setting of the mirror elements and of the polarization-influencing optical arrangement, an actual distribution of the Stokes vector in the pupil plane; and modifying the setting of the mirror elements and/or of the polarization-influencing optical arrangement on the basis of a comparison between the actual distribution and the desired distribution, wherein in the comparison between the actual distribution and desired distribution, a component of the Stokes vector that describes the intensity is weighted more heavily than the components of the Stokes vector that respectively describe a degree of polarization.

Description

Microlithographic exposure method, and microlithographic projection exposure apparatus

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Application DE 10 2012 214 052.2 and US 61/680,751 , both filed on August 8, 2012. The content of these applications is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a microlithographic exposure method, and to a microlithographic projection exposure apparatus. In particular, the invention relates to a microlithographic exposure method which makes it possible to flexibly provide a desired polarization distribution in an efficient manner that is as free from errors as possible (i.e. with as little loss of light as possible and without disturbing artifacts).

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 any 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 the need to set defined illumination settings, i.e. intensity distributions in a pupil plane of the illumination device, in a targeted manner. Alongside the use of diffractive optical elements (so-called DOEs), the use of mirror arrangements comprising a multiplicity of mirror elements that can be set independently of one another is also known for this purpose, e.g. from WO 2005/026843 A2.

Furthermore, various approaches are known for setting specific polarization distributions in the pupil plane and/or in the reticle in a targeted manner in the illumination device for the purpose of optimizing the imaging contrast, such as e.g. a so-called tangential polarization distribution, in which the oscillation planes of the electric field strength vectors of the individual linearly polarized light rays are oriented approximately perpendicularly to the radius directed to the optical system axis. With regard to the prior art, reference is made by way of 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 and DE 10 2004 01 1 733 A1 . For flexibly setting the polarization distribution, too, it is possible to use, in particular, a polarization-influencing optical arrangement in conjunction with a mirror arrangement embodied as mentioned above. In this case, for setting a desired polarized illumination setting (also designated hereinafter as "target pupil") it is necessary to determine the respectively suitable setting both of the mirror arrangement (i.e. the tilting angle of the individual mirror elements) and of the polarization-influencing optical arrangement. This determination of the settings of mirror arrangement and polarization-influencing optical arrangement in order to produce a predefined target pupil is also designated hereinafter as "matching". In this case, it is conventionally possible, in particular, in a first step, to divide the polarized illumination setting to be set into a number of subpupils, wherein e.g. each of said subpupils has a constant preferred direction of polarization corresponding to one of (a total of n) "elementary polarization states" that can be set by means of the respective polarization-influencing optical arrangement. In this case, it is possible e.g. with these polarization states (for n=4) for the preferred direction of polarization to be oriented by 45°, 90°, -45° or 0° with respect to the y-direction relative to a predefined coordinate system.

In this case, however, in practice the problem occurs, inter alia, that the decomposition of a predefined target pupil into subpupils firstly is generally not possible in an unambiguous manner and secondly, under certain circumstances, is also not possible in an exact manner, with the result that a target pupil deviating from the target pupil actually desired is possibly generated, which can in turn lead to disturbing artifacts in the polarized illumination setting actually set and to an impediment of the imaging behavior of the projection exposure apparatus.

Further problems that arise in practice result from the fact that, in the case of the abovementioned combination of mirror arrangement and polarization-influencing optical arrangement, depending on the concrete configuration of the polarization-influencing optical arrangement, the allocation of a defined polarization state to the mirror elements is possible e.g. only in groups or in clusters (e.g. in lines). This in turn has the consequence that in the mirror arrangement there are mirror elements which possibly do not match the intensity ratios corresponding to the desired illumination setting and cannot be used for an optimum realization of the respective desired distribution of the intensity and of the polarization state in a pupil plane of the illumination device. However, a "deflection" of the mirror elements that are correspondingly "not required" from the pupil plane results in a loss of light, thereby impairing the performance of the projection exposure apparatus and also reducing the throughput of the lithography process.

Furthermore, unavoidable deviations from the desired target pupil result in noise in the set polarized illumination setting, which can also increase in the case of the abovementioned composition of the target pupil comprising subpupils, since the deviations for the individual subpupils then add up.

SUMMARY OF THE INVENTION

Against the above background, it is an object of the present invention to provide a microlithographic exposure method and a microlithographic projection exposure apparatus which make it possible for a desired polarization distribution to be provided flexibly and as far as possible without any errors in an efficient manner (that is to say with as little loss of light as possible).

This object is achieved in accordance with the method in accordance with the features of independent Claim 1 and the apparatus in accordance with the features of Claim 6.

A microlithographic exposure method in which light generated by means of a light source is fed to an illumination device of a projection exposure apparatus for illuminating an object plane of a projection lens and in which the object plane is imaged into an image plane of the projection lens by means of the projection lens, wherein at least one mirror arrangement having a plurality of mirror elements, which are adjustable independently of one another for varying an angular distribution of the light reflected by the mirror arrangement, and a polarization-influencing optical arrangement are used in the illumination device, comprises the following steps: determining, for a predefined desired distribution of the intensity and of the polarization state in a pupil plane of the illumination device, a desired distribution of the Stokes vector in said pupil plane; determining, for a current setting of the mirror elements and of the polarization-influencing optical arrangement, an actual distribution of the Stokes vector in the pupil plane; and modifying the setting of the mirror elements and/or of the polarization-influencing optical arrangement on the basis of a comparison between the actual distribution and the desired distribution, wherein in the comparison between the actual distribution and desired distribution, a component (So) of the

Stokes vector that describes the intensity is weighted more heavily than the components (Si , S2) of the Stokes vector that respectively describe a degree of polarization. In this case, in accordance with customary terminology the Stokes vector consists of the four components So, Si , S2 and S3 (also designated as Stokes parameters), wherein So corresponds to the intensity I, Si and S2 describe linearly polarized light and S3 describes circularly polarized light. The invention is based on the concept, in particular, in a projection exposure apparatus comprising a mirror arrangement and a polarization-influencing optical arrangement, that the determination of the settings of these arrangements that are suitable for generating a desired target pupil (i.e. the "matching" process described above) is not carried out separately for individual subpupils, rather that in a uniform matching process for each location of the pupil plane, a matching of the Stokes vector respectively obtained there is performed instead.

This uniform matching process on the basis of the Stokes vectors obtained for the individual locations of the pupil plane leads, in comparison with carrying out separate matching processes for individual subpupils, to reduced noise in the polarized illumination setting ultimately set (as explained below on the basis of an exemplary comparative calculation), a smaller loss of light or intensity, and to a smaller extent of undesirable artifacts.

In principle, a polarization distribution, as already mentioned, can be established by four basic polarization states pi-p₄, in which the preferred direction of polarization is oriented at an angle of 90° (=pi), -45° (=P2), 0° (=p₃) or 45°(=p ) e.g. with respect to the y-direction relative to a predefined coordinate system, that is to say that the following holds true: P(x,y) = p₁ -a(x,y) + p₂ -b(x,y) + p₃ -c(x,y) + p₄ -d(x,y) (1)

The case may then be considered, by way of example, where the abovementioned matching process is intended to be carried out for an unpolarized pupil. In the event of separate matching processes being carried out in a conventional manner for individual subpupils, the following holds true in this case for the target pupil

P(x,y) = p₁ - (x,y) + p₃-c(x,y), where a(x,y) = c(x,y) (2) The following holds true for the "matched" pupil

P(x, y) = p_x - a(x, y) + p₃ - c(x, y) (3) thus resulting in (apart from non-relevant coefficient factors) a deviation of

AP(x, y)~p_x - Aa(x, y) + p₃ - Ac(x, y) (4)

In the case where the mirror arrangement is composed of N mirror elements, N/2 mirror elements are respectively used for a(x,y) and c(x,y). The deviations are therefore

Aa(x,y) = \/^N/2, Ac(x,y) = l/jN/2 (5) The relationship with the Stokes representation is

(*, y) = , y) + ^c(^x, y), s_x (x, y) = (x, y) - c(x, y) (6) The deviation of the "matched" Stokes parameters is therefore

AS₀ (x, y) = V2 / VNV2 = 1 / N = 2 / VN (7)

AS, (x,y) = V2/VNV2 = 1/ NV4 = 21 N (8)

If, by contrast, in the manner according to the invention, the matching process is carried out for the Stokes vector as such, then in the abovementioned example N mirror elements are available for the "matching" of So and Si . The expected deviations are therefore only

AS₀ (x,y) = l/ N, AS_l (x,y) = \/jN (9)

Consequently, the expected deviations for the approach according to the invention (with the matching process being carried out for the Stokes vector as such) are only half the magnitude of those in the case of the conventional approach of carrying out separate matching processes for individual subpupils.

The invention exploits the fact, in particular, that with the use of the Stokes formalism the freedom is maintained to represent a specific polarization state differently as a linear combination of elementary polarization states (in which for instance, according to the example mentioned above, the respective preferred direction of polarization runs at an angle of 45°, 90°, -45° or 0° with respect to the y-direction relative to a predefined coordinate system).

In accordance with the disclosure, in the comparison between the actual distribution and desired distribution, a component of the Stokes vector that describes the intensity is weighted more heavily than the components that respectively describe a degree of polarization. In this case, the invention is based on the insight - obtained during an assessment of the imaging properties - that the setting of the intensity distribution is accorded greater importance than that of the polarization distribution, in other words the microlithography process in the image or wafer plane thus reacts more sensitively to intensity fluctuations than to polarization fluctuations. In other words, proceeding from the Stokes vector defined above, the total intensity described by the Stokes parameter So is of greater importance than the Stokes parameters Si and S₂ for the imaging properties or the contrast obtained in the wafer plane.

In accordance with one embodiment, modifying the setting of the mirror elements and/or of the polarization-influencing optical arrangement is effected iteratively until the deviation between the respective Stokes vectors of actual distribution and desired distribution, said deviation being averaged over the pupil plane, falls below a predefined threshold value. In particular, therefore, the setting of the mirror elements and of the polarization-influencing optical arrangement can be varied with minimization of the deviation between the respective Stokes vectors of actual distribution and desired distribution, said deviation being averaged over the pupil plane.

In this case, the setting of the mirror elements and the setting of the polarization-influencing optical arrangement can be varied in particular simultaneously during this iteration. As a result, it is generally possible to achieve the smallest deviation between target pupil and polarized illumination setting actually set, a lower speed of the numerical method being accepted.

In accordance with a further embodiment, the iteration can also comprise a first iteration phase for iteratively setting the polarization-influencing optical arrangement and a temporally succeeding second iteration phase for iteratively setting the mirror elements. As a result, a higher speed of the numerical method can be achieved in comparison with the abovementioned simultaneous iteration with regard to the setting of the mirror elements and the setting of the polarization-influencing optical arrangement. In this embodiment, by way of example, in the first iteration phase it is possible to effect integration in each case over all linear combinations of elementary polarization states, wherein maximum freedom is maintained for the second iteration phase, i.e. the optimization of the setting of the mirror elements. The invention furthermore relates to a microlithographic projection exposure apparatus, comprising an illumination device and a projection lens, wherein the illumination device has a mirror arrangement having a plurality of mirror elements, which are adjustable independently of one another for varying an angular distribution of the light reflected by the mirror arrangement, and a polarization-influencing optical arrangement, and comprising a control device, which is designed to carry out a method having the features described above.

The polarization-influencing optical arrangement can be realized in any suitable manner, as will be explained in even greater detail below. By way of example, the polarization-influencing optical arrangement can have optical components, which are adjustable in terms of their relative position with respect to one another, wherein different output polarization distributions can be generated by this adjustment in conjunction with the mirror arrangement, without a polarization manipulator having to be exchanged or additional optical components being required for the change between these illumination settings.

In particular, the optical components can be adjustable relative to one another with a degree of overlap that is variable in the light propagation direction. The optical components can be, for example, lambda/2 plates or else components composed of optically active material, in particular composed of crystalline quartz having an orientation of the optical crystal axis that is parallel to the light propagation direction. In accordance with a further embodiment, the polarization-influencing optical arrangement can be a periodic arrangement of regions that bring about a rotation of the direction of polarization of impinging light, wherein this periodic arrangement is asymmetric with respect to the optical axis in a first spatial direction perpendicular to the optical axis.

The polarization-influencing optical arrangement can be arranged in particular between the mirror arrangement and a pupil plane of the illumination device at a position at which the condition 0.3 < |S| < 0.8 is fulfilled for the paraxial subaperture ratio S.

In accordance with one embodiment, the polarization-influencing optical arrangement can be exchangeable. In particular, the polarization-influencing optical arrangement can be exchangeable for at least one other polarization-influencing optical arrangement having a different (in relation to the first polarization-influencing optical arrangement) periodic arrangement of the regions that bring about a rotation of the direction of polarization of impinging light, with the result that, in this configuration of the polarization-influencing optical arrangement, too, a settability of the polarization-influencing effect thereof is provided.

In accordance with one embodiment, the polarization-influencing optical arrangement is designed in such a way that a defined polarization state can be allocated to at least one portion of the mirror elements only in groups. The invention can be used particularly advantageously in this case since then the "quantization" in the allocation of the polarization state by the polarization-influencing optical arrangement and thus generally also the number of mirror elements that are surplus per se when generating the desired distribution of the intensity and the polarization state in the pupil plane is comparatively large, such that the avoidance of a loss of intensity according to the invention is also particularly effective. Further configurations of the invention can be gathered from the description and the dependent claims. The invention is explained in greater detail below on the basis of exemplary embodiments illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

shows a schematic illustration of the exemplary construction of a microlithographic projection exposure apparatus in which a method according to the invention can be realized; Figure 2 shows a schematic illustration for elucidating the construction and function of the mirror arrangement present in the projection exposure apparatus from Figure 1 ; shows a schematic illustration for elucidating an embodiment of a polarization-influencing optical arrangement that can be used in the method according to the invention;

Figure 4 shows a flowchart for elucidating an embodiment of the method according to the invention; and

Figures 5-8 show schematic illustrations of further embodiments of a polarization-influencing optical arrangement that can be used in the context of the method according to the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Firstly, with reference to Fig. 1 , an exemplary construction of a microlithographic projection exposure apparatus comprising an optical system according to the invention is explained below. The projection exposure apparatus has 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, more particularly less than 200 nm. According to the invention, part of the illumination device 10 is, in particular, a mirror arrangement 120, as will be explained in greater detail below with reference to Fig. 2. A polarization-influencing optical arrangement 1 10, explained in even greater detail below with reference to Fig. 3 et seq., is arranged upstream of the mirror arrangement 120 in the light propagation direction. In further alternative embodiments, the polarization-influencing optical arrangement 1 10 can also be arranged downstream of the mirror arrangement 120 relative to the light propagation direction.

In accordance with Fig. 1 , provision is furthermore made of a respective driving unit 1 15 and 125 for driving an adjustment of the polarization-influencing optical arrangement 1 10 and of the mirror arrangement 120 by means of suitable actuators. Such actuators can be configured in any suitable manner, e.g. as belt drives, flexure elements, piezo-actuators, linear drives, direct-current (DC) motors with or without gearing, 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. A light mixing device (not illustrated) is situated in the beam path downstream of the optical unit 1 1 in the light propagation direction, which light mixing device can have, for example, in a manner known per se, an arrangement of micro-optical elements that is suitable for achieving light mixing, and also 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 . Fig. 2 shows, for elucidating the construction and function of the mirror arrangement 120 used in the illumination device 10, an exemplary construction of a partial region of the illumination device 10, which comprises successively in the beam path of a laser beam 210 a deflection mirror 21 1 , a refractive optical element (ROE) 212, a lens element 213 (depicted merely by way of example), a microlens element arrangement 214, the mirror arrangement 120, a diffuser 215, a lens element 216 and the pupil plane PP. The mirror arrangement 120 comprises a multiplicity of mirror elements 120a, 120b, 120c, and the microlens element arrangement 214 has a multiplicity of microlens elements for targeted focusing onto said micromirrors and for reducing or avoiding an illumination of "dead surface area". The mirror elements 120a, 120b, 120c, can in each case be tilted individually, e.g. in an angular range of -2° to +2°, in particular -5° to +5°, more particularly -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 quadrupole setting, can be formed in the pupil plane PP by virtue of the previously homogenized and collimated laser light being directed respectively in the corresponding direction by the mirror elements 120a, 120b, 120c, ... depending on the desired illumination setting.

Fig. 3 serves firstly to elucidate the interaction of the polarization-influencing optical arrangement 1 10, already mentioned in connection with Fig. 1 , with the mirror arrangement 120 in accordance with one exemplary embodiment. In this case, the polarization-influencing optical arrangement 1 10 has three mutually independently adjustable components 1 1 1 , 1 12, 1 13 in the form of optical rotators composed of optically active crystalline quartz, which components can be introduced into the beam path in each case perpendicularly to the light propagation direction, wherein each of said rotators by itself brings about a rotation of the preferred direction of polarization by 45° for light passing through. Consequently, the preferred direction of polarization is rotated by 45° upon passage of light through only one rotator 1 1 1 , 1 12 or 1 13, by 90° upon passing through two of said rotators, and by 135° (or -45°) upon passing through all of the rotators. This rotation is likewise illustrated in Fig. 3, wherein the double-headed arrows depicted for the partial beams S10-S40 respectively designate the preferred direction of polarization as seen in the z-direction (when viewed in the x-y plane). In this case, the partial beam S10 passes through none 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. Fig. 3 likewise illustrates only schematically the microlens element arrangement 105, which, as mentioned above, focuses 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, wherein, in further exemplary embodiments, the microlens element arrangement 105 can also be arranged downstream of the polarization-influencing optical arrangement

1 10 in the light propagation direction.

An exemplary embodiment of the method according to the invention for setting the polarization-influencing optical arrangement 1 10 and the mirror arrangement 120 is explained below with reference to the flowchart illustrated in Fig. 4.

In accordance with Fig. 4, a first step S410 involves determining a desired distribution of the Stokes vector for a predefined target pupil, i.e. a predefined desired distribution of the intensity and of the polarization state in a pupil plane of the illumination device. A second step S420 then involves determining an actual distribution of the Stokes vector in the pupil plane for a current setting of the mirror elements 120a, 120b, 120c, ... and of the polarization-influencing optical arrangement 1 10, which can be effected either by measurement or by way of a calculation or simulation. Finally a third step S430 involves modifying the setting of the mirror elements and of the polarization-influencing optical arrangement on the basis of a comparison between the actual distribution and the desired distribution.

Further possible embodiments of a polarization-influencing optical arrangement that can be used in combination with a mirror arrangement in the context of the present invention are explained below with reference to Fig. 5 et seq.

Fig. 5a-c serve for elucidating an embodiment of a polarization-influencing optical arrangement 500 that can be used in the context of the present invention. This arrangement, as can best be seen from Fig. 5c, is embodied as a periodic arrangement of strip-shaped regions composed of optically active material that bring about a rotation of the direction of polarization of impinging light. This periodic arrangement is asymmetrical with respect to the optical axis OA in a first spatial direction perpendicular to the optical axis OA (in accordance with Fig. 5a, b, said spatial direction is the y-direction). Furthermore, said polarization-influencing optical arrangement

500 is arranged between the mirror arrangement 120 and a pupil plane PP of the illumination device at a position at which the condition 0.3 < ISI < 0.8 is fulfilled for the paraxial subaperture ratio S. In this case, the paraxial subaperture ratio S is defined as

S = -^sgn (h) (10)

M r where r denotes the paraxial marginal ray height and h denotes the paraxial chief ray height, sng(x) denotes the so-called signum function, wherein by definition sgn(0) = 1 can be set. A definition of the paraxial marginal ray and paraxial chief ray is indicated in "Fundamental Optical Design" by Michael J. Kidger, SPIE PRESS, Bellingham, Washington, USA.

On account of the positioning in the region between field plane and pupil plane, it is possible to dispense with a further dynamically adjustable element and in this case nevertheless to realize the flexible setting of the illumination setting in the pupil plane both with regard to the intensity distribution or the pupil filling and with regard to the polarization distribution set. As can best be seen from Fig. 5c, the arrangement 500 comprises, in plan view, first strip-shaped regions 500a, which extend along the x-direction and in which the direction of polarization is rotated, wherein second strip-shaped regions 500b, in which the direction of polarization is not rotated, are arranged between said first strip-shaped regions 500a. The configuration of the arrangement 500 with the strip structure described is particularly advantageous in so far as such a component can be produced from optically active material significantly more simply in terms of production engineering than, for instance, a component having a two-dimensional grid arrangement.

The arrangement 500 is configured with utilization of the optical activity by virtue of the manipulator elements in each case being produced from optically active material, in particular from crystalline quartz having an optical axis of the crystal material that is oriented parallel to the light propagation direction or optical system axis. The optical axis of crystalline quartz is understood to mean that axis for which light propagating along said axis brings about the maximum rotation of the electric field strength vector of linearly polarized light passing through the crystal on account of the optical activity of the crystal material. In this case, the optically active material brings about a rotation of the direction of polarization which is proportional to the path length respectively covered within the optically active material, such that the thickness of the respective region composed of optically active material determines the polarization rotation.

It will now be assumed below, without restricting the generality, that the laser light impinging on the polarization-influencing optical arrangement 500 originally is linearly polarized in the y-direction, this direction of polarization being rotated by 90° in the regions 500a, whereas it remains unchanged in the regions 500b of the polarization-influencing optical element 500. Consequently, if a partial beam impinges on one of the mirrors of the mirror arrangement 120, then the polarization-influencing optical arrangement 500, depending on the tilting angle currently set for said mirror, thus either leaves the direction of polarization of said partial beam unchanged or rotates said direction of polarization by an angle of 90°. By means of suitable adjustment of the mirror elements by means of the guiding unit 155, said adjustment being coordinated with the polarization-influencing optical arrangement 500, a flexible and rapid changeover between different illumination settings can now be achieved.

This is effected, in accordance with Fig. 5a-c, using a single polarization-influencing optical arrangement of simple construction, or construction requiring only little outlay in terms of production engineering, in combination with a mirror arrangement composed of mutually independently adjustable mirror elements for different polarization distributions, wherein the polarization-influencing optical arrangement remains fixed in position in the optical system and, therefore, neither has to be adjusted in terms of its position nor has to be exchanged for another arrangement or another element. The arrangement 500 can also be configured as settable or displaceable, in particular exchangeable, in further embodiments. In particular, the arrangement can be exchangeable for at least one other arrangement having a different (in relation to the first arrangement 500) periodic arrangement of the regions that bring about the rotation of the direction of polarization of impinging light.

Fig. 6 shows, in a schematic illustration, a further embodiment of a polarization-influencing optical arrangement 600 that can be used in the context of the present invention. In the exemplary embodiment, the polarization-influencing optical arrangement 600 comprises lambda/2 plates 610, 620 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). In this case, the first lambda/2 plate 610 can have a first fast axis of birefringence and the second lambda/2 plate 620 can have a second fast axis of birefringence, wherein the first fast axis and the second fast axis are arranged at an angle of 45°±5° with respect to one another. The first lambda/2 plate 610 and the second lambda/2 plate 620 can form a 90° rotator in the region of overlap with one another and can be adjustable in terms of their relative position with respect to one another, such that they have a variable degree of overlap in the light propagation direction. In the exemplary embodiment in accordance with Fig. 6, in this case the fast axis of birefringence of the first lambda/2 plate 610 runs at an angle of 22.5°±2° with respect to the preferred direction P of polarization of the light beam impinging on the arrangement 600 (i.e. with respect to the y-direction), and the fast axis of birefringence of the second lambda/2 plate 620 runs at an angle of -22.5°±2° with respect to the preferred direction P of polarization of the light beam impinging on the arrangement 600.

Fig. 6 likewise depicts, for the case of the incidence of linearly polarized light having a constant preferred direction P of polarization running in the y-direction, the preferred directions of polarization respectively arising after light passes through the polarization-influencing optical arrangement 600. In this case, the respectively arising preferred direction of polarization is designated by P' for the first non-overlap region "B-1 " (i.e. the region covered only by the first lambda/2 plate 610), by P" for the second non-overlap region "B-2" (i.e. the region covered only by the second lambda/2 plate 620), and by P'" for the overlap region "A" (i.e. the region covered both by the first lambda/2 plate 610 and by the second lambda/2 plate 620).

The preferred directions P' and P" of polarization arising after light passes through the non-overlap regions "B-1 " and "B-2", respectively, run at an angle of ±45° with respect to the preferred direction P of polarization of the light beam incident on the polarization-influencing optical arrangement 600. For the light beam impinging on the arrangement 600 in the overlap region "A" it holds true that the preferred direction P' of polarization of the light beam emerging from the first lambda/2 plate 610 corresponds to the input polarization distribution of the light beam impinging on the second lambda/2 plate 620, such that the preferred direction of polarization - designated by P'" in Fig. 6 - of the light beam emerging from the overlap region "A" runs at an angle of 90° with respect to the preferred direction P of polarization of the light beam impinging on the arrangement 600. The positioning of the lambda/2 plates 610, 620 and the distance thereof from the mirror arrangement 120 should furthermore be chosen in each case such that the light portions impinging on the individual mirrors of the mirror arrangement 120 are well defined with regard to the polarization state in as much as one defined polarization state - rather than, for instance, two or more mutually different polarization states - is applied to the light reflected at a respective one of the mirrors of the mirror arrangement 120. Fig. 7 shows, as a further embodiment, a polarization-influencing optical arrangement 700 composed of two rotatable lambda/2 plates 710 and 720. Actuators for rotating the lambda/2 plates 710 and 720 can be configured in any desired manner e.g. as belt drives, flexure elements, piezo-actuators or combinations of these known components. In accordance with Fig. 7, the advantage is afforded that two polarization states having an arbitrary preferred direction of polarization can be set by means of the two rotatable lambda/2 plates 710 and 720. In the region of overlap of the lambda/2 plates 710 and 720, a further, third polarization state results from the combined effect of the two lambda/2 plates 710 and 720 analogously to Fig. 6.

In accordance with further embodiments, the optical system can also have more than two lambda/2 plates, wherein generally arrangements having an arbitrary number (> 2) of lambda/2 plates with arbitrary orientation of the fast axis of birefringence can be provided.

A further possible embodiment of the polarization-influencing optical arrangement will be explained with reference to Fig. 8a-b. In this embodiment, a channel-by-channel setting of the polarization is made possible by virtue of the fact that, as can be seen in Fig. 8a, a polarization-influencing optical arrangement 800 is provided in addition to a mirror arrangement 120 having a plurality of mirror elements, said polarization-influencing optical arrangement having, in accordance with Fig. 8b, a grid- or matrix-like arrangement of cells which enable a flexible and dynamic changeover of the polarization and which are designed as Kerr cells in the exemplary embodiment. In accordance with Fig. 8a, the polarization-influencing optical arrangement 800 is arranged downstream of the mirror arrangement 120 in the light propagation direction and constitutes, in particular, the next optical element in the light propagation direction with respect to the mirror arrangement 120. Each of the Kerr cells in the polarization-influencing optical arrangement 800 enables, in a manner known per se, by variation of an externally applied electric field, a controllable modulation of the polarization of the light passing through, as is clarified in the schematic illustration in Fig. 8b by polarization states set in the individual cells, said polarization states being indicated by way of example in each case. In accordance with a further embodiment, the cells can also be configured as Pockels cells which are produced from a suitable crystal material having sufficient transmission at the operating wavelength (e.g. KDP = potassium dihydrogen phosphate, KH₂P0₄) and enable a polarization manipulation on account of the linear proportionality of the birefringence present in the crystal material with respect to the externally applied electric field. The configuration of the polarization-influencing optical arrangement 800 having the plurality of Kerr cells (or Pockels cells) can furthermore be periodic or non-periodic, wherein in particular the dimensions of the individual Pockels cells within the polarization-influencing optical arrangement 800 can also vary over the optically used region. 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

Microlithographic exposure method in which light generated by means of a light source is fed to an illumination device of a projection exposure apparatus for illuminating an object plane of a projection lens and in which the object plane is imaged into an image plane of the projection lens by means of the projection lens, wherein at least one mirror arrangement (120) having a plurality of mirror elements (120a, 120b, 120c, ...), which are adjustable independently of one another for varying an angular distribution of the light reflected by the mirror arrangement (120), and a polarization-influencing optical arrangement (1 10, 500, 600, 700, 800) are used in the illumination device (10), wherein the method comprises the following steps: a) determining, for a predefined desired distribution of the intensity and of the polarization state in a pupil plane of the illumination device (10), a desired distribution of the Stokes vector (S) in said pupil plane; b) determining, for a current setting of the mirror elements (120a, 120b, 120c, ...) and of the polarization-influencing optical arrangement (1 10, 500, 600, 700, 800), an actual distribution of the Stokes vector in the pupil plane; and c) modifying the setting of the mirror elements (120a, 120b, 120c, ...) and/or of the polarization-influencing optical arrangement (1 10, 500, 600, 700, 800) on the basis of a comparison between the actual distribution and the desired distribution, wherein in the comparison between the actual distribution and desired distribution, a component (So) of the Stokes vector that describes the intensity is weighted more heavily than the components (Si , S2) of the Stokes vector that respectively describe a degree of polarization.

Method according to Claim 1 , characterized in that modifying the setting of the mirror elements (120a, 120b, 120c, ...) and/or of the polarization-influencing optical arrangement (1 10, 500, 600, 700, 800) is effected on the basis of a deviation between the respective Stokes vectors of actual distribution and desired distribution, said deviation being averaged over the pupil plane.

Method according to Claim 1 or 2, characterized in that modifying the setting of the mirror elements (120a, 120b, 120c, ...) and/or of the polarization-influencing optical arrangement (1 10, 500, 600, 700, 800) is effected iteratively until the deviation between the respective Stokes vectors of actual distribution and desired distribution, said deviation being averaged over the pupil plane, falls below a predefined threshold value.

Method according to Claim 3, characterized in that the setting of the mirror elements (120a, 120b, 120c, ...) and the setting of the polarization-influencing optical arrangement (1 10, 500, 600, 700, 800) are varied simultaneously during this iteration.

Method according to Claim 3, characterized in that this iteration comprises a first iteration phase for iteratively setting the polarization-influencing optical arrangement (1 10, 500, 600, 700, 800) and a temporally succeeding second iteration phase for iteratively setting the mirror elements (120a, 120b, 120c, ...).

Microlithographic projection exposure apparatus, comprising an illumination device (10) and a projection lens (20), wherein the illumination device (10) has a mirror arrangement (120) having a plurality of mirror elements (120a, 120b, 120c, ...), which are adjustable independently of one another for varying an angular distribution of the light reflected by the mirror arrangement (120), and a polarization-influencing optical arrangement (1 10, 500, 600, 700, 800), and comprising a control device, which is designed to carry out a method according to any of the preceding claims.

7. Microlithographic projection exposure apparatus according to Claim 6, characterized in that the polarization-influencing optical arrangement (1 10) is designed in such a way that a defined polarization state can be allocated to at least one portion of the mirror elements (120a, 120b, 120c, ...) only in groups.

8. Microlithographic projection exposure apparatus according to Claim

7, characterized in that the polarization-influencing optical arrangement (1 10) has optical components (1 1 1 , 1 12, 1 13), which are adjustable in terms of their relative position with respect to one another, wherein different output polarization distributions can be generated by this adjustment in conjunction with the mirror arrangement (120).

9. Microlithographic projection exposure apparatus according to Claim

8, characterized in that said optical components (1 1 1 , 1 12, 1 13) are adjustable relative to one another with a degree of overlap that is variable in the light propagation direction.

10. Microlithographic projection exposure apparatus according to Claim 8 or 9, characterized in that different polarization rotation angles of the preferred direction of polarization of light passing through which correspond to an integral multiple of 22.5°, in particular to an integral multiple of 45°, can be set by this adjustment.

1 1 . Microlithographic projection exposure apparatus according to any of Claims 8 to 10, characterized in that said optical components (1 1 1 ,

1 12, 1 13) are produced from optically active material, in particular from crystalline quartz having an orientation of the optical crystal axis that is parallel to the light propagation direction. Microlithographic projection exposure apparatus according to any of Claims 8 to 10, characterized in that said optical components are lambda/2 plates.

Microlithographic projection exposure apparatus according to Claim 6, characterized in that the polarization-influencing optical arrangement (500) is a periodic arrangement of regions that bring about a rotation of the direction of polarization of impinging light, wherein this periodic arrangement is asymmetric with respect to the optical axis (OA) in a first spatial direction perpendicular to the optical axis (OA).

Microlithographic projection exposure apparatus according to Claim 13, characterized in that the polarization-influencing optical arrangement (500) is arranged between the mirror arrangement (100) and a pupil plane (PP) of the illumination device at a position at which the condition 0.3 < |S| < 0.8 is fulfilled for the paraxial subaperture ratio S.

Microlithographic projection exposure apparatus according to Claim 13 or 14, characterized in that the polarization-influencing optical arrangement (500) can be exchanged for at least one polarization-influencing optical arrangement having a different periodic arrangement of the regions that bring about a rotation of the direction of polarization of impinging light.