WO2013013894A1

WO2013013894A1 - Microlithographic exposure method

Info

Publication number: WO2013013894A1
Application number: PCT/EP2012/061608
Authority: WO
Inventors: Martin Meier; Ingo SÄNGER
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2011-07-26
Filing date: 2012-06-18
Publication date: 2013-01-31
Also published as: DE102011079777A1

Abstract

The invention relates to a microlithographic exposure method, wherein at least one mirror arrangement (200) having a plurality of mirror elements that are adjustable independently of one another for altering an angular distribution of the light reflected by the mirror arrangement, and a polarization manipulator (100, 600, 700, 800) are used in an illumination device (10). A method according to the invention 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 (10), an orientation of first mirror elements of the mirror arrangement (200), which orientation is suitable for generating said desired distribution, wherein a group composed of one or a plurality of in this case surplus second mirror elements of the mirror arrangement (200) remains; determining an orientation of said second mirror elements which is suitable for at least approximately generating the desired distribution of the intensity; and modifying the determined orientation of the first mirror elements in a manner dependent on the determined orientation of the second mirror elements.

Description

Microlithographic exposure method

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Application DE 10 201 1 079 777.7 and US 61/51 1 ,612, both filed on July 26, 201 1 . The content of these appli- cations is hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the invention

The invention relates to a microlithographic exposure method. In particular, the invention relates to a microlithographic exposure method which makes it possible to flexibly provide a desired polarization distribution as far as possible without loss of light.

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 sub- strate (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. In 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, e.g. from WO 2005/026843 A2, apart from the use of diffractive optical elements (so-called DOEs) it is also known to use mirror arrangements comprising a multiplicity of mi- cromirrors that can be set independently of one another.

Furthermore, various approaches are known for setting in the illumination device for optimizing the imaging contrast in a targeted manner specific polarization distributions in the pupil plane and/or in the reticle, 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 toward 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 and DE 10 2004 01 1 733 A1 .

For flexibly setting the polarization distribution, too, a polarization manipulator can be used in connection with a mirror arrangement. In this case, however, in practice the problem occurs that, in such a combination of mirror arrangement and polarization manipulator, the light reflected at the mirror elements of the mirror arrange- ment can be allocated the polarization by means of the polarization manipulator only in a "quantized" manner in so far as the allocation - depending on the concrete configuration of the polarization manipulator - is possible e.g. only group by group or cluster by cluster (e.g. line by line), but at least only in steps of one mirror in each case. This in turn has the consequence that in the mirror arrangement there are mirror elements which are possibly not appropriate for the intensity ratios corresponding to the desired illumination setting and should not 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. In this case, "intensity ratios" are taken to mean the ratios with respect to one another of the intensities of the (n) uniform subpupils into which the target pupil can be subdivided according to the (n) polarization directions that can be set. "Diverting" the corresponding mirror elements out of the pupil plane results in a loss of light, whereby the imaging behavior of the projection exposure apparatus is adversely affected.

SUMMARY OF THE INVENTION Against the above background, a problem addressed by the present invention is that of providing a microlithographic exposure method which makes it possible to flexibly provide a desired polarization distribution as far as possible without loss of light. This problem is solved in accordance with the features of independent claim 1 .

A microlithographic exposure method, wherein 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 wherein the object plane is im- aged 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 that are adjustable independently of one another for altering an angular distribution of the light reflected by the mirror arrangement, and a polarization manipulator 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, an orientation of first mirror elements of the mirror arrangement, which orientation is suitable for generating said desired distribution, wherein a group composed of one or a plurality of in this case surplus second mirror elements of the mirror ar- rangement remains; - determining an orientation of said second mirror elements which is suitable for at least approximately generating the desired distribution of the intensity; and

- modifying the determined orientation of the first mirror elements in a manner dependent on the determined orientation of the second mirror elements.

The invention is based on the concept, in particular, that such mirror elements which, as explained in the introduction, are surplus per se for setting the respective desired distribution of the intensity and of the polarization state in a pupil plane of the illumination device or appear not to be appropriate for the intensity ratios to be set in the pupil plane are nevertheless used for the imaging process and, in this case, certain losses with regard to the polarization distribution obtained are deliberately accepted. In this case, the invention proceeds from the insight that in the assessment of the imaging properties it has been found that setting the intensity distribution is accorded greater importance than the polarization distribution, that is to say, in other words, that the contrast obtained in the microlithography process in the image or wafer plane reacts more sensitively to intensity fluctuations than to polarization fluctuations.

According to the invention, in particular, the mirrors which are "surplus" per se for setting the respective desired distribution of the intensity and of the polarization state can firstly be distributed with regard to their orientation over that region of the pupil plane which is to be illuminated and the respective intensity contributions of these "surplus" mirrors can then be subtracted from the original desired intensity distribution, such that in the latter as it were an "intensity gap" is produced or allowed for, toward which said surplus mirrors can be oriented. The polarization manipulator can be realized in any suitable manner, as will be explained in greater detail below. By way of example, the polarization manipulator can comprise at least two lambda/2 plates which are adjustable relative to one an- other by translational movement and/or rotation and which are arranged one behind another in the optical system relative to the light propagation direction, such that different initial polarization distributions can be generated in combination with the mirror arrangement by means of the variation of the degree of overlap of the lambda/2 plates and, consequently, mutually different polarized illumination settings can be set in conjunction with the mirror arrangement in a flexible manner, without the polarization manipulator having to be exchanged or additional optical components being required for the change between said illumination settings. A transmission loss associated with the use of additional optical components is also avoided as a result.

In accordance with one embodiment, when determining the orientation of the second mirror elements, the polarization state allocated to the light reflected at said mirror elements by means of the polarization manipulator is disregarded. In other words, when determining the orientation of the second mirror elements that are initially surplus per se, the procedure involves pretending as though the polarization manipulator were not present, as a result of which the method is simplified and account is furthermore taken of the circumstance mentioned in the introduction that possible polarization fluctuations or errors when setting the polarization distribution predefined by the desired distribution affect the imaging contrast ultimately obtained less seriously than intensity fluctuations.

However, the invention is not restricted thereto (i.e. to disregarding the influence of the polarization manipulator in the orientation of the second mirror elements). In a further embodiment, therefore, when determining the orientation of the second mirror elements, the polarization state allocated to the light reflected at said second mirror elements by the polarization manipulator can also be taken into account, for instance to the effect that a second mirror element that is respectively to be oriented is not oriented toward a location in the pupil plane at which the desired po- larization state is precisely orthogonal with respect to the polarization state actually allocated to this mirror element, but rather at least approximately corresponds to the actually allocated polarization state. By way of example, consideration can be given to ensuring that a second mirror element that is respectively to be oriented is directed at a location of the pupil plane at which the desired preferred polarization direction, albeit not identical to the preferred polarization direction allocated to the mirror element, nevertheless deviates by not more than ±45°, for example. In accordance with one embodiment, the polarization manipulator is designed in such a way that a defined polarization state can be allocated only group by group to at least one portion of the mirror elements. In this case, the invention can be used particularly advantageously since then the "quantization" in the allocation of the polarization state by the polarization manipulator and thus generally also the number of mirror elements that are surplus per se when generating the desired distribution of the intensity and of the polarization state in the pupil plane are comparatively large, such that the avoidance of a transmission loss according to the invention is also particularly effective. However, the invention is not restricted thereto (i.e. to a respective polarization state being possibly allocated only group by group or cluster by cluster by means of the polarization manipulator). This is because the problem addressed according to the invention of the quantization of the allocation of a polarization state by means of the polarization manipulator exists not only when allocating the polariza- tion state to a group or a "cluster" composed of a plurality of mirror elements, but also already when allocating a respective polarization state to each individual one of the mirror elements.

In accordance with one embodiment, in the modifying step, the respective intensity contributions of the second mirrors for the determined suitable orientation of said second mirrors are subtracted in a suitable manner from the desired distribution of the intensity taken as a basis in the first step. The wording "in a suitable manner" should be understood here to mean that a pure subtraction is suitable for the case where the target pupil can be subdivided into subpupils in a non-overlapping man- ner (that is to say that no pupil regions with mixed states occur). Consequently, the respective intensity contributions of the second mirrors, for the orientation of the first mirror elements that is ultimately to be chosen, are "biased" in the desired distribution of the intensity in order, as a result, to set the optimum intensity distribu- tion whilst accepting certain losses with regard to the polarization distribution, but in return whilst avoiding loss of light.

In accordance with one embodiment, in the first step, determining a suitable orien- tation of first mirror elements of the mirror arrangement is carried out for a plurality of intensity distributions in the pupil plane, wherein each of said intensity distributions corresponds to a different polarization state that can be set by means of the polarization manipulator. In other words, the definition and also the later modification of the desired distribution of the intensity in the pupil plane are effected in the form of "subpupils", which are each characterized in that the preferred polarization direction is constant for each of said subpupils.

In accordance with one embodiment, it can furthermore be taken into account that, in an illumination device having a diffractive optical element (DOE) for flexibly set- ting an illumination setting, a stray light background typically occurs, wherein the intensity of said stray light background can be, for example, of the order of magnitude of 1 % of the total intensity of the illumination light. In practice, it may be desirable, then, when simulating a specific illumination setting, also to simulate or to "emulate" said stray light background. For this purpose, the second mirror ele- ments (which are "not required" or surplus per se for generating the predefined desired distribution of the intensity and of the polarization state) of the mirror arrangement can now likewise be used, it being possible to make use of the circumstance that the intensity of the above-described stray light background and the intensity of the light reflected at the second mirror elements are of the same order of magnitude or match one another well.

In accordance with one embodiment, therefore, the orientation of the second mirror elements determined in the method according to the invention is constituted in such a way that a predefined straight line background is emulated by the light re- fleeted at the second mirror elements.

In principle, the concept according to the invention is applicable to any illumination device which makes possible a quantized setting of the polarization direction for spots, or regions to be illuminated, that are to be arranged freely in the pupil plane. In other words, the invention is not necessarily restricted to the presence of a mirror arrangement. In accordance with a further aspect, therefore, the invention also relates to a microlithographic exposure method, wherein 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 wherein the object plane is imaged into an image plane of the projection lens by means of the projection lens, wherein the illumination device enables different settings that differ from one another with regard to the distribution of the intensity and of the polarization state, which distribution is generated in a pupil plane of the illumination device, wherein the method comprises the following steps:

- determining, for a predefined desired distribution of the intensity and of the polarization state in the pupil plane of the illumination device, a first setting of the illumination device, which first setting is suitable for generating said desired distribution; and

- operating the illumination device with a second setting modified relative to the first setting, wherein the second setting is chosen in such a way that a light loss present in the first setting in the course of generating the desired distribution is reduced at the expense of a greater deviation from the de- sired distribution of the polarization state by comparison with the first setting.

The invention furthermore relates to a microlithographic projection exposure apparatus, comprising an illumination device and a projection lens, wherein the illumi- nation device has a mirror arrangement having a plurality of mirror elements that are adjustable independently of one another for altering an angular distribution of the light reflected by the mirror arrangement, and a polarization manipulator, and comprising a control device for the mirror arrangement, which is designed to carry out a method comprising the features described above.

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 figures.

BRI EF DESCRIPTION OF THE DRAWINGS

In the figures: Figure 1 shows a schematic illustration for elucidating the construction of a microlithographic projection exposure apparatus comprising a mirror arrangement and a polarization manipulator, in which apparatus 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 ;

Figures 3-4 show schematic illustrations for elucidating an embodiment of the method according to the invention;

Figure 5 shows a flowchart for elucidating an embodiment of the method according to the invention; and Figures 6-8 show schematic illustrations of different exemplary embodiments of a polarization manipulator that can be used in the method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODI MENTS

Firstly, with reference to Fig. 1 , a basic contribution 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 an 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 200, as is explained in greater detail below with reference to Fig. 2. A polarization manipulator 100, which will be explained in greater detail below with reference to Fig. 6 et seq., is arranged upstream of the mirror arrangement 200 in the light propagation direction. In further alternative embodiments, the po- larization manipulator 100 can also be arranged downstream of the mirror arrangement 200 relative to the light propagation direction.

In accordance with Fig. 1 , provision is furthermore made of a driving unit 105 for driving an adjustment of the arrangement 100 by means of suitable actuators. Ac- tuators for adjusting the arrangement 100 can be configured in any desired manner, e.g. as belt drives, solid-state articulation 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 an 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 par- ticular greater than 1.1 .

The mirror arrangement 200 has a plurality of mirror elements 200a, 200b, 200c, ... in the construction illustrated schematically in Fig. 2. The mirror elements 200a, 200b, 200c, ... are adjustable independently of one another for altering an angular distribution of the light reflected by the mirror arrangement 200, wherein, in accordance with Fig. 1 , provision can be made of a driving unit 205 for driving this adjustment (e.g. by means of suitable actuators).

Fig. 2 shows, for elucidating the construction and function of the mirror arrange- ment 200 used according to the invention in the illumination device 10, an exemplary construction of a partial region of the illumination device 10, this comprising, 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 200, a diffuser 215, a lens element 216 and the pupil plane PP. The mirror arrangement 200 comprises a multiplicity of micromirrors 200a, 200b, 200c, ... , 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 micromirrors 200a, 200b, 200c, ... an 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 micromirrors 200a, 200b, 200c, ... in the mirror arrangement 200, a desired light distribution, e.g. an annular illumination setting or else a dipole setting or a quad- rupole setting, can be formed in the pupil plane PP by virtue of the previously ho- mogenized and collimated laser light being directed respectively in the corresponding direction by the micromirrors 200a, 200b, 200c, ... depending on the desired illumination setting. The method according to the invention will now be explained in greater detail below in an exemplary embodiment with reference to the schematic illustration of Fig. 3. Fig. 3 on the left illustrates firstly an arbitrary desired polarized illumination setting, i.e. an intensity distribution to the set in the pupil plane with specific preferred polarization directions in the regions of the pupil plane that are to be illuminated. This illumination setting is merely by way of example, and the invention can be realized analogously with any arbitrary other illumination setting. In the concrete example illustrated, a freeform illumination setting is involved, in which, proceeding from a quadrupole illumination setting with four illumination poles offset by 90° with respect to one another, additional regions are illuminated with an intensity not equal to zero, to be precise both regions offset by 45° with respect to said illumination poles and a central region of the pupil plane. The polarization distribution chosen in the exemplary embodiment should likewise be understood without restriction of generality and without restriction of the invention, the example involving a quasi-tangential polarization distribution in which in the center unpolarized light is generated (by superimposition of mutually orthogonal polarization states).

In the exemplary embodiment, then, this polarization distribution is established by four polarization states p1 -p4, in which the preferred polarization direction relative to the coordinate system illustrated is oriented by 45° (=p1 ), 90° (=p2), -45° (=p3) and 0°(=p4), respectively, in relation to the y-direction.

In order, then, to generate this polarized illumination setting with the mirror arrangement 200 illustrated on the right in Fig. 3, some of the mirror elements then prove to be surplus and accordingly should actually be sorted out - for the optimum realization of the polarization distribution from Fig. 3. These mirror elements are respectively designated by an "x" on the right in Fig. 3. It goes without saying that the number and arrangement of the mirror elements are merely by way of example, wherein a mirror arrangement can also have fewer or more (typically sig- nificantly more, e.g. more than 1000) mirror elements.

In accordance with Fig. 5, then, in a first step S1 , the polarized illumination setting to be set (designated hereinafter as "desired pupil" P for the sake of simplicity) is divided into n subpupils SP1 , SPn, wherein n corresponds to the number of "elementary" polarization states which can be set by means of the respective polarization-influencing optical arrangement. In this case, each of the subpupils is characterized in that it has a constant preferred polarization direction - namely corresponding to one of the "elementary" polarization states p1 -p4.

In a second step S2, in the mirror arrangement the mirror elements that are surplus (because they are "non-required" for the optimum setting of the polarization distribution in the "desired pupil" P), i.e. in the example of Fig. 3 the mirror ele- ments identified by an "X", are identified. The extent to which mirror elements of the mirror arrangement are to be sorted out or are not required per se can be intensified, in particular, by virtue of the fact that, depending on the constitution of the polarization manipulator used in conjunction with the mirror arrangement, under certain circumstances, not all of the mirror elements independently of one an- other can be allocated a specific polarization direction, but rather only a group or a cluster of a plurality of mirror elements all at once. However, even in configurations in which all of the mirror elements independently of one another can be allocated a specific polarization direction, one or a plurality of mirror elements can remain as "not required" in the above sense, depending on the constitution of the polarized illumination setting to be set.

The next step S3 then involves a "matching" of the intensity distribution of the target pupil P with these "non-required" mirror elements, to be precise in such a way that the polarization state of the light directed onto the pupil plane by said mirror elements is disregarded. In this case, the relevant "non-required" mirror elements are oriented only to those regions of the pupil plane in which an intensity not equal to zero is also intended to be present in the desired pupil P. The relevant mirror elements can be oriented by means of algorithms such as are well known to the person skilled in the art for setting the mirror elements of a mirror arrangement and which typically involve displacing the mirror orientations into the pupil plane in a simulated manner and numerically seeking a best possible solution. One such pupil optimization algorithm is disclosed e.g. in US 2010/0265482 A1 . The intensity distribution established by means of the "non-required" mirror elements in step S3 is then subtracted in a suitable manner, in the next step S4, from each of the subpupils SP1 -SPn determined in step S1 , modified subpupils SP1 ', SPn' being obtained.

Step S5 then involves a "matching" of these modified subpupils SP1 ', SPn' with the non-identified mirror elements (i.e. those not provided with an "X" in Fig. 3), that is to say that for these non-identified mirror elements (i.e. those regarded from the outset as "required") the corresponding orientation is determined in order to generate the modified subpupils SP1 ', SPn'.

As a result, therefore, step S5 yields the orientation to be set of the mirror elements regarded as "required" from the outset. Since the orientation to be set of the mirror elements initially regarded as "not required" has already been defined in step S3, the orientations of all mirror elements are thus defined as a result of the method from Fig. 5.

Fig. 6 shows in a schematic illustration a polarization manipulator 600 in accordance with one embodiment of the invention. In the exemplary embodiment, the polarization manipulator 600 comprises lambda/2 plates 610, 620, which partly overlap one another and which are in each case produced from a suitable birefrin- gent material having sufficient transparency at the desired operating wavelength, for example from magnesium fluoride (MgF₂), sapphire (AI2O3) or crystalline quartz (Si0₂). In this case, the first lambda/2 plate 610 can have a first fast axis of bire- fringence 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 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 polarization direction P 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 polarization direction P 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 polarization direction P running in the y-direction, the preferred polarization directions respectively arising after light passage through the polarization manipulator 600. In this case, the preferred polarization direction re- spectively arising 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 polarization directions P' and P" arising after light passage through the non-overlap regions "B-1 " and "B-2", respectively, run at an angle of ±45° with respect to the preferred polarization direction P of the light beam impinging on the arrangement 600. For the light beam impinging on the arrangement 600 in the overlap region "A", it holds true that the preferred polarization direction P' 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 polarization direction - 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 polarization direction P 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 200 should furthermore be chosen in each case such that the light proportions impinging on the individual mirrors of the mirror arrangement 200 are well-defined with regard to the polarization state in the sense that the light reflected respectively at one of the mirrors of the mirror arrangement 200 is sub- jected to one defined polarization state - rather than for instance to two or more mutually different polarization states.

Fig. 7 shows, as a further embodiment, an arrangement composed of two ro- tatable 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, solid- state articulation elements, piezo-actuators or combinations of these known components. In accordance with Fig. 7, the advantage is afforded that two polarization states with any desired preferred polarization direction 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 any desired number (> 2) of lambda/2 plates having any desired orientation of the fast axis of birefringence can be provided.

A further embodiment of the present invention is explained below with reference to Fig. 8. In this embodiment, a channel-by-channel setting of the polarization is made possible by virtue of the fact that, as is evident from Fig. 8, in addition to a mirror arrangement 200 having a plurality of mirror elements, a manipulator 800 is provided, which has a raster- or matrix-like arrangement of cells enabling a flexible and dynamic changeover of the polarization, said cells being designed as Kerr cells in the exemplary embodiment. In accordance with Fig. 8, the manipulator 800 is arranged downstream of the mirror arrangement 200 in the light propagation direction and constitutes, in particular, the closest optical element following in the light propagation direction with respect to the mirror arrangement 200. Each of the Kerr cells in the manipulator 800 enables a controllable modulation of the polariza- tion of the light passing through in a manner known per se by means of the variation of an externally applied electric field. 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 manipulator 800 having the plurality of Kerr cells (or Pockels cells) can furthermore be a periodic or else a non-periodic arrangement, wherein, in particular, the dimensions of the individual Pockels cells within the manipulator 800 can also vary over the optically used region of the manipulator 800.

Even though the invention has been described on the basis of specific embodi- ments, 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 . Microlithographic exposure method, wherein light generated by means of a light source is fed to an illumination device (10) of a projection exposure apparatus for illuminating an object plane of a projection lens (20) and wherein the object plane is imaged into an image plane of the projection lens (20) by means of the projection lens (20), wherein at least one mirror arrangement (200) having a plurality of mirror elements that are adjustable independently of one another for altering an angular distribution of the light reflected by the mirror arrangement, and a polarization manipulator (100, 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), an orientation of first mirror elements of the mirror arrangement (200), which orientation is suitable for generating said desired distribution, wherein a group composed of one or a plurality of in this case surplus second mirror elements of the mirror arrangement (200) remains;

b) determining an orientation of said second mirror elements which is suitable for at least approximately generating the desired distribution of the intensity; and

c) modifying the orientation of the first mirror elements determined in step a) in a manner dependent on the orientation of the second mirror elements determined in step b).

2. Method according to Claim 1 , characterized in that, in step b), the polarization state allocated to the light reflected at the second mirror elements by means of the polarization manipulator is disregarded.

Method according to Claim 1 , characterized in that, in step b), the polarization state allocated to the light reflected at the second mirror elements by means of the polarization manipulator is taken into account.

Method according to any of Claims 1 to 3, characterized in that the polarization manipulator is designed in such a way that a defined polarization state can be allocated only group by group to at least one portion of the mirror elements.

Method according to any of the preceding claims, characterized in that, in step c), modifying is effected on the basis of a suitable subtraction of the respective intensity contributions of the second mirror elements for the suitable orientation of said second mirror elements determined in step b) from the desired distribution of the intensity taken as a basis in step a).

Method according to any of the preceding claims, characterized in that, in step a), determining a suitable orientation of first mirror elements of the mirror arrangement (200) is carried out for a plurality of intensity distributions in the pupil plane, wherein each of said intensity distributions corresponds to a different polarization state that can be set by means of the polarization manipulator.

Method according to any of the preceding claims, characterized in that the orientation of the second mirror elements determined in step b) is constituted in such a way that a predefined stray light background is emulated by the light reflected at the second mirror elements.

Microlithographic exposure method, wherein light generated by means of a light source is fed to an illumination device (10) of a projection exposure apparatus for illuminating an object plane of a projection lens (20) and wherein the object plane is imaged into an image plane of the projection lens (20) by means of the projection lens (20), wherein the illumination device (10) enables different settings that differ from one another with regard to the distribution of the intensity and of the polarization state, which distribution is generated in a pupil plane of 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 the pupil plane of the illumination device (10), a first setting of the illumination device (10), which first setting is suitable for generating said desired distribution; and

• operating the illumination device (10) with a second setting modified relative to the first setting, wherein the second setting is chosen in such a way that a light loss present in the first setting in the course of generating the desired distribution is reduced at the expense of a greater deviation from the desired distribution of the polarization state by comparison with the first setting.

9. Microlithographic projection exposure apparatus, comprising an illumination device and a projection lens, wherein the illumination device has a mirror arrangement (200) having a plurality of mirror elements that are adjustable independently of one another for altering an angular distribution of the light reflected by the mirror arrangement, and a polarization manipulator (100, 600, 700, 800), and comprising a control device for the mirror arrangement (200), which is designed to carry out a method according to any of the preceding claims.