Illumination optics and methods for measuring the dependence of the intensity of illumination light incident on an object field on at least one detection object field coordinate using such illumination optics

Abstract

An illumination optic (11) has two faceted mirrors (6, 7) for reflecting illumination light (2) from an EUV light source (2). The second faceted mirror (7) has second individual mirrors (34) that form second facets (25), which, via partial beams (3i) of the illumination light (3), image groups of individual mirrors (26) of the first faceted mirror (6), which form first facets, at least into partial fields of an object field (8). An intensity sensor device (31) serves to measure the dependence of the intensity of the illumination light (3) incident on the object field (8) on at least one detection object field coordinate (x). This sensor device has sensor individual mirrors (21s) of the first faceted mirror (6) that are assigned to several different object field positions (xi) along the detection object field coordinate (x).The individual sensor mirrors (21s) are designed to reflect the illumination light (3) towards the intensity sensors (32i) of the intensity sensor device (31). This results in an illumination optic in which a corresponding intensity-coordinate dependency measurement is enabled precisely or in parallel with the operational use of the illumination optic.

Description

The invention relates to an illumination optical system having two facet mirrors. The invention further relates to a method for measuring a dependence of an intensity of illumination light impinging on an object field on at least one detection object field coordinate using such an illumination optical unit.An illumination optical system of the type mentioned at the beginning is known from DE 10 2015 208 512 A1.It is an object of the present invention to further develop an illumination optical unit of the type mentioned at the beginning and a measurement method for this in such a way that a measurement of a dependence of an intensity of illumination light impinging on the object field on at least one detection object field coordinate is made possible precisely and / or parallel to a useful operation of the illumination optical unit.This object is achieved according to the invention by an illumination optical system having the features specified in claim 1 and by a measurement method having the features specified in claim 6.According to the invention, it has been recognized that in the case of illumination optics having two facet mirrors, in particular in the case of illumination optics in which at least one of the two facet mirrors is designed as a MEMS mirror having a very large number of individual mirrors, the great flexibility in the assignment of the individual mirrors of the two facet mirrors to guide the illumination light within the illumination optics usually means that specific individual mirrors of the first facet mirror are not used for projection exposure within the illumination optics. Illumination light which falls onto these individual mirrors of the first facet mirror can be used in the illumination optical unit according to the invention for measuring a dependence of an intensity of illumination light impinging on an object field on at least one detection object field coordinate. In this case, the realization is used that the individual mirrors of the first facet mirror that are not used for object field illumination allow, on account of their arrangement on the first facet mirror, a conclusion to be drawn as to which object field coordinate used for projection exposure, which individual mirrors are adjacent to these sensor individual mirrors, illuminate along the detection object field coordinate to be measured. This realization, which allows an assignment of the respective sensor individual mirrors to the object field coordinate to be detected and the realization that a far-field illumination intensity dependence over the first facet mirror changes regularly, viewed over the dimension of an individual mirror, only slightly, leads to the possibility, with the aid of the intensity sensor device of the illumination optics, of carrying out, on the one hand, a precise measurement of the dependence of the illumination intensity on the detection object field coordinate and, on the other hand, to the possibility of carrying out the measurement parallel to the useful operation of the illumination optics.By assigning the first facets to the second facets, in particular an illumination setting can be predefined, that is to say an illumination angle distribution of the illumination of the object field. The illumination intensity distribution over the object field coordinate to be detected can be dependent on the selected illumination setting and it can therefore be necessary to monitor this illumination intensity distribution in a setting-dependent manner and, if appropriate, to correct it.Short-term intensity changes can also be detected during the useful operation as part of ongoing monitoring with the intensity sensor device and can optionally be corrected.The illumination optics can be embodied with a field facet mirror and a pupil facet mirror, in which the second facet mirror is arranged in the region of a pupil plane of the illumination optics. Alternatively, the illumination optics can also be designed in the manner of a specular reflector, in which the second facet mirror is arranged at a distance from an illumination pupil plane.The intensity sensor device can be used in particular as a field-resolving UNICOM sensor. A corresponding device for influencing a uniformity of an illumination intensity via the field height can then be controlled via the intensity sensor device. Such an influencing device, which is also known as UNICOM, is known from EP 0 952 491 A2.The intensity sensors of the intensity sensor device can correspond to the second facets as far as their boundary shape and / or as far as their surface are concerned. A loss of light due to transmission over the second facets, i.e. if illumination light beyond the second facets is lost, is then similarly high as a loss of light due to transmission over the intensity sensors. In particular, a configuration can be achieved in which the sensor signal of the intensity sensors remains proportional to the intensity of the illumination light arriving in the object field even if a light loss of the object field illumination, for example due to drifts of the EUV light source, is variable over time.If the illumination optics is designed such that a configuration of the second facets and in particular the number and arrangement of the second individual mirrors forming the second facets in each case is variable depending on the illumination configuration, the assigned intensity sensors can likewise have a variable size or a variable boundary shape, adapted to this size variability. Such a variable size or boundary shape of the intensity sensors can be achieved by presetting intensity sensors of different sizes. Alternatively or additionally, a variability of the size or the boundary shape of the intensity sensors can be achieved by means of diaphragms in the illumination light beam path assigned in each case by the intensity sensors in front of the intensity sensors and / or by means of a pixel design of the intensity sensors, wherein, depending on the size and shape of the second facets, such pixelated intensity sensors are read out only in each case at the sensor pixels which correspond in their arrangement to the size or shape of the second facets.Numbers of intensity sensors according to claim 2 enable sufficient spatial resolution in the detection object field coordinate to be measured depending on the requirement profile. The number of intensity sensors can be in the range between 4 and 100, in the range between 5 and 50, for example in the range of 10 or in the range of 25, when measuring a detection object field coordinate. If two field dimensions are measured, if for example the far field in which the first facet mirror is arranged is to be measured with the aid of the intensity sensor device, the number of intensity sensors can also be greater than 100 and can lie in the range between 100 and 1000.An arrangement of the intensity sensors according to claim 3 uses that the illumination light is present in the region of the second individual mirrors regularly in facet-channel-wise bundled form, since there in the typical application an at least approximate imaging of the light source into an arrangement plane of the second facet mirror takes place. The arrangement of the intensity sensors adjacent to the second individual mirrors of the second facet mirror then leads to the possibility of arranging the intensity sensors compactly next to one another.A sensor row according to claim 4 is particularly compact.An arrangement of the individual sensor mirrors according to claim 5 enables a 2D far-field measurement, wherein the measurement positions of the individual sensor mirrors serve as measurement nodes, starting from which an extrapolation can then be carried out in order to determine the entire 2D far field.The advantages of a method according to claim 6 correspond to those already explained above in connection with the illumination optics.This results in an in particular precise measurement of the dependence of the intensity of the illumination light on the detection object field coordinate, which can take place in particular parallel to a useful operation of the illumination optical unit. In order to prepare the evaluation step of the measurement method, the intensity sensors can be calibrated, for example using an illumination arrangement with constant illumination intensity via the detection object field coordinate. The evaluation step can be followed by a correction step in which an individual mirror assignment or else a facet assignment is changed such that an actual value of an illumination intensity distribution approaches a setpoint value via the detection object field coordinate. The resulting correction can be effected in particular such that an illumination angle distribution of an illumination of the object field by the illumination optical unit remains unchanged on account of the correction.The advantages of the method according to claim 7 correspond to those of the illumination optics according to claim 5.The advantages of an illumination system according to claim 8, an optical system according to claim 9, a projection exposure apparatus according to claim 10, a production method according to claim 11 and a micro- or nanostructured component according to claim 12 correspond to those already explained above with reference to the illumination optics according to the invention or the measurement method according to the invention. Due to the precisely measured and optionally corrected illumination intensity distribution over the detection object field coordinate, the possibility of a particularly precise and high-resolution component production results. In the production method according to claim 11, the above-discussed measurement method can be used in particular for presetting an optimized illumination setting.In particular, a semiconductor component in the form of a microchip, in particular a memory chip, can be produced.Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. In these show: FIG. 1 shows a highly schematic meridional section of a projection exposure apparatus for EUV microlithography with a light source, an illumination optical unit and a projection optical unit, wherein a plan view of an object field of the projection exposure apparatus is illustrated in an insert; FIG. 2 shows schematically and likewise in meridional section a beam path of selected individual beams of illumination light within the illumination optics according to FIG. 1, starting from an intermediate focus up to a reticle or object arranged in the object plane of the projection optics in the region of the illumination or object field; FIG. 3 shows a plan view of a section of a first facet mirror of the illumination optical unit of the projection exposure apparatus, wherein an individual mirror group of the first facet mirror, which forms a first facet, is highlighted, said individual mirror group being imaged into the object field by means of a partial beam of the illumination light via individual mirrors of a second facet mirror of the illumination optical unit, which form a second facet; FIG. 4 shows, in a representation similar to FIG. 3, a section of a further embodiment of the first facet mirror, again with a single mirror group emphasized, which is imaged as a first facet into the object field via an associated second facet of the second facet mirror; FIG. 5 shows, in a representation similar to FIGS. 3 and 4, a plan view of the first facet mirror with an arrangement of individual mirrors corresponding to FIG. 4, wherein an occupancy of the first facet mirror with first facets, each formed from individual mirror groups, is illustrated, which are imaged in the object field in a manner overlapping one another, wherein sensor individual mirrors of an intensity sensor device for measuring a dependence of an intensity of the illumination light impinging on the object field on a detection object field coordinate are additionally emphasized between these individual mirror groups; FIG. 6 shows schematically and in perspective an embodiment of the illumination optics of the projection exposure apparatus with the first facet mirror and the second facet mirror, wherein an illumination light beam path between a light source and an intensity sensor of an intensity sensor sensor row of the intensity sensor device, guided via one of the sensor individual mirrors of the first facet mirror, is illustrated; FIG. 7 shows a diagram which shows a correlation N G( ordinate) of the field height coordinates x within a respective column of a column-by-column assignment of the individual mirror groups of a variant of the first facet mirror to field heights x of the object field of the first facet mirror (abscissa), when setting an illumination setting "y-dipole", wherein the assignment of the individual mirrors to the field heights x leads to a total of eight individual mirror columns (j=1,... 8); FIG. 8 shows an example of a distribution of the sensor individual mirrors on a variant of the first facet mirror with a very much larger individual mirror number compared to FIG. 5, again in a plan view; FIG. 9 shows a graph of a field height dependence of a setpoint illumination intensity I SOLL( dashed) over the object field and an as yet uncorrected actual illumination light intensity I IST( solid); FIG. 10 shows, in a representation similar to FIG. 9, intensity measurement values of the intensity sensors over the sensor row according to FIG. 6, wherein correction measurement values I K( dashed) for the case of the desired illumination intensity according to FIG. 9 and actual measurement values I M( solid) for the case of the still uncorrected illumination intensity distribution according to FIG. 9 ; and FIG. 11 shows a comparison of relative changes in the field height dependencies on the one hand during the illumination with the actual illumination intensity according to FIG. 9 as a relative intensity deviation I IST( dashed) and on the other hand as a relative measured value deviation I ISTM between the two measurement curves according to FIG. 10 (solid), to illustrate a measurement quality of the intensity sensor device which can be used for a subsequent correction.A projection exposure apparatus 1 for microlithography, which is illustrated in a highly schematic manner in FIG. 1 and in a meridional section, has a light source 2 for illumination light 3. This can be an LPP (laser produced plasma) light source, a DPP (discharge produced plasma) light source or a synchrotron radiation-based light source, for example a free electron laser (FEL).A transmission optics 4 is used for guiding the illumination light 3, starting from the light source 2, and this optics have a collector 5, which is illustrated in FIG. 1 only with regard to its reflecting effect, and a transmission facet mirror 6, which is described in more detail below and is also referred to as a first facet mirror or as a field facet mirror. Between the collector 5 and the transmission facet mirror 6, an intermediate focus 5 aof the illumination light 3 is arranged. A numerical aperture of the illumination light 3 in the region of the intermediate focus 5 ais, for example, NA=0.182. Arranged downstream of the transfer facet mirror 6 and thus of the transfer optics 4 is an illumination-specification facet mirror 7, which is also referred to as a second or further facet mirror and is likewise explained in more detail below. The optical components 5 to 7 are components of an illumination optical unit 11 of the projection exposure apparatus 1.The transmission facet mirror 6 is arranged in a field plane of the illumination optical unit 11 in a far field of illumination light of the light source 2.The illumination-specification facet mirror 7 of the illumination optical unit 11 is arranged at a distance from pupil planes of the illumination optical unit 11. Such an arrangement is also referred to as a specular reflector.In an alternative embodiment of the illumination optics, the second facet mirror 7 can also be arranged in a pupil plane of the illumination optics 11 and is a pupil facet mirror in this case.Arranged downstream of the illumination specification facet mirror 7 in the beam path of the illumination light 3 is an object to be illuminated in the form of a reticle 12 which is arranged in an object plane 9 of a downstream projection optical unit 10 of the projection exposure apparatus 1. The projection optical unit 10 is a projection objective. With the illumination optics 11, an object field 8 on the reticle 12 is illuminated in a defined manner in the object plane 9. The object field 8 simultaneously represents an illumination field of the illumination optical unit 11. In general, the illumination field is designed such that the object field 8 can be arranged in the illumination field.The illumination-specification facet mirror 7 is, like the transmission facet mirror 6, part of a pupil illumination unit of the illumination optical unit and serves for illuminating an entry pupil 12 ain a pupil plane 12 bof the projection optical unit 10 with the illumination light 3 having a predefined pupil intensity distribution. The entrance pupil 12 aof the projection optical unit 10 can be arranged in the illumination beam path upstream of the object field 8 or else downstream of the object field 8. FIG. 1 shows the case in which the entry pupil 12 ais arranged in the illumination beam path downstream of the object field 8. A pupil distance PA of the second facet mirror 7 from the pupil plane 12 bis obtained in this case as the sum of a z-distance PA 1 of the second facet mirror 7 from the object plane 9 and the z-distance PA 2 of the object plane 9 from the pupil plane 12 b. Thus, in the z-direction, PA=PA1+PA2 applies. The pupil distance PA can also be measured in the beam direction.To facilitate the representation of positional relationships, a Cartesian xyz-coordinate system is used below. The x-direction extends in FIG. 1 perpendicularly to the plane of the drawing into the latter. The y-direction extends to the right in FIG. 1. The z-direction runs downward in FIG. 1. Coordinate systems used in the drawing each have x-axes running parallel to one another. The course of a z-axis of these coordinate systems follows a respective main direction of the illumination light 3 within the respectively observed figure.The object field 8 has an arcuate or partially circular shape and is bounded by two circular arcs parallel to one another and two straight side edges which run 0 in the y direction with a length y and are at a distance x 0 to one another in the x direction. The aspect ratio x 0 / y 0 is 13 to 1. an insert of FIG. 1 shows a top view, not to scale, of the object field 8. In an alternative and likewise possible object field 8, its boundary shape is rectangular, likewise with aspect ratio x 0 / y 0.During a projection exposure, the reticle 12 is displaced along an object displacement direction y through the object field 8.The projection optical unit 10 is indicated only partially and strongly schematically in FIG. 1. An object field-side numerical aperture 13 and an image field-side numerical aperture 14 of the projection optical unit 10 are illustrated. Further optical components of the projection optical unit 10, not illustrated in FIG. 1, for guiding the illumination light 3 are situated between these optical components 15, 16, between indicated optical components 15, 16 of the projection optical unit 10, which optical components can be embodied, for example, as mirrors reflecting for the EUV illumination light 3.The projection optical unit 10 images the object field 8 into an image field 17 in an image plane 18 on a wafer 19 which, like the reticle 12, is carried by a holder, not shown in detail. Both the reticle holder and the wafer holder can be displaced both in the x direction and in the y direction by means of corresponding displacement drives. A structural space requirement of the wafer holder is illustrated in FIG. 1 at 20 as a rectangular box. The installation space requirement 20 is rectangular with an extent in the x-, y- and z-directions which depends on the components to be accommodated therein. The installation space requirement 20 extends, for example, from the center of the image field 17, in the x-direction and in the y-direction by 1 m. The installation space requirement 20 also extends, for example, from the image plane 18 in the z-direction by 1 m.The illumination light 3 must be guided in the illumination optical unit 11 and the projection optical unit 10 in such a way that it is guided past the installation space requirement 20, respectively.The transfer facet mirror 6 has a plurality of transfer facets, also referred to as first facets. The transfer facet mirror 6 can be embodied as a MEMS mirror. The transfer facets are individual mirrors 21 which can be switched at least between two tilting positions and are designed as micromirrors. The individual mirrors 21 can be designed as tiltable micromirrors driven about two mutually perpendicular axes of rotation.Of these individual mirrors 21, a line with a total of nine individual mirrors 21 is schematically shown in the yz section according to FIG. 2, which are indicated from left to right in FIG. 2 by 21 1 to 21 9. In fact, the transfer facet mirror 6 has a substantially larger plurality of the transfer facets 21. The transfer facets 21 are grouped into a plurality of transfer facet groups, not shown in more detail in FIG. 2. These transfer facet groups are also referred to as single mirror groups, virtual field facets or virtual facet groups.Each of the transmission facet groups guides a portion of the illumination light 3, which is also referred to as illumination light sub-bundle, via an illumination channel for partial or complete illumination of the object field 8. In principle, each of the illumination specification facets 25 can in turn be constructed from a plurality of individual mirrors. The illumination specification facets 25 are also referred to below as second facets.For further details of possible embodiments of the transfer facet mirror 6 and of the projection optical unit 10, reference is made to WO 2010 / 099 807 A.At least some of the illumination specification facets 25 illuminate only a sub-region or sub-field of the object field 8. These sub-fields are shaped very individually and also depend on the desired illumination direction distribution (pupil shape) in the object field 8, i.e. the illumination setting. The illumination specification facets 25 are therefore illuminated by virtual field facets of very different shapes, the shape of which corresponds precisely to the shape of the respective sub-field to be illuminated. Each illumination specification facet 25 also contributes to different regions of the pupil depending on the location in the object field 8.The illumination specification facet mirror 7 can be designed as a MEMS mirror in particular when each of the illumination specification facets 25 is constructed from a plurality of individual mirrors. The illumination specification facets 25 are micromirrors switchable between at least two tilt positions. The illumination specification facets 25 are designed as micromirrors which can be tilted continuously and independently driven about two mutually perpendicular tilting axes, that is to say can be set into a multiplicity of different tilting positions.An example of a predefined assignment of individual transfer facets 21 to the illumination specification facets 25 is illustrated in FIG. 2. The illumination specification facets 25 assigned to the transmission facets 21 1 to 21 9 in each case are indexed in accordance with this assignment. The illumination facets 25 are illuminated from left to right on the basis of this assignment in the sequence 25 6, 258, 253, 254, 251, 257, 255, 252 and 25 9.Indices 6, 8 and 3 of facets 21, 25 include three illumination channels VI, VIII and III, which illuminate three object field points OF 1, OF 2, OF 3, which are numbered from left to right in FIG. 2, from a first illumination direction. The indices 4, 1 and 7 of the facets 21, 25 belong to three further illumination channels IV, I, VII, which illuminate the three object field points OF 1 to OF 3 from a second illumination direction. The indices 5, 2 and 9 of the facets 21, 25 belong to three further illumination channels V, II, IX, which illuminate the three object field points OF 1 to OF 3 from a third illumination direction.The illumination directions,the illumination channels VI, VIII, III,the illumination channels IV, I, VII andthe illumination channels V, II, IXThe respective components are assigned to them, are identical. The assignment of the transmission facets 21 to the illumination specification facets 25 is therefore such that telecentric illumination of the object field 8 results in the illumination example illustrated in the figure.The illumination of the object field 8 via the transmission facet mirror 6 and the illumination-specification facet mirror 7 can take place in the manner of a specular reflector. The principle of the specular reflector is known from US 2006 / 0132747 A1.FIG. 3 schematically shows a plan view of a section of the first facet mirror 6 with square first facets 21, which are arranged in an array tilted by 45° with respect to the xy-coordinate system. The rows and columns of this array arrangement thus run at a 45° angle to the x- and y-directions, respectively.Emphasized in FIG. 3 is an individual mirror group 26 having individual mirrors 21 G1 to 21 G11, which is imaged as a first facet into the object field 8 via a respectively assigned second facet 25 of the second facet mirror 15.The individual mirrors 21 Gi of the individual mirror group 26 are located within an arc-field-shaped group boundary 27 of the individual mirror group 26. In fact, the number of individual mirrors 21 Gi belonging to a respective individual mirror group 26 is significantly larger in practice and can be, for example, in the range between 15 and 50 or even larger.Within the group boundary 27, some individual mirrors 21 of the first facet mirror 6 are situated only partially. Here, a tilting of the respective individual mirror 21 can be decided by a corresponding control of the illumination optical unit 11 whether or not these individual mirrors 21 lying partially in the group boundary 27 should belong to the individual mirror group 26. For example, those individual mirrors 21 which lie with at least 60% of their reflection surface or else, as indicated in FIG. 3, with at least 100% of their reflection surface within the group boundary 27 can be assigned to the individual mirror group 26. In the region of, in particular, a reflection surface proportion of 50% per individual mirror 21, which lies within the group boundary 27, there are some individual mirrors 21, which in this selection criterion cannot be assigned either to the individual mirror group 26 emphasized in FIG. 3 or to an adjoining individual mirror group, since the reflection surface of such individual mirrors 21, which lie on the boundary of the group boundary 27, reaches the minimum surface boundary within the respective group boundary 27 in the group assignment shown for no individual mirror groups. Some of these individual mirrors 21 are highlighted in FIG. 3 as potential sensor individual mirrors 21 in S fashion. Potential sensor individual mirrors 21 of this kind are S with respect to an imaging of adjacent individual mirrors 21 into the object field 8, assigned to different field heights x i of the individual mirror group 26, that is to say different x coordinates of the individual mirror group 26 imaged into the object field 8. These potential sensor individual mirrors 21 sthus represent an illumination intensity of the illumination light far field which regularly varies only slightly over the location coordinates x, y of the field facet mirror 6 along an individual mirror extension and in which the field facet mirror 6 is arranged, at the location of in each case an associated field height x i of a detection object field coordinate x.These potential individual sensor mirrors 21 S are each directly adjacent to the individual group mirrors 21 Gi of the individual mirror group 26.FIG. 4 shows, in a representation similar to FIG. 3, a variant of the first facet mirror 6. components and functions which correspond to those which have already been explained above with reference to FIGS. 1 to 3 and in particular with reference to FIG. 3 have the same reference numerals and are not discussed in detail again.The field facet mirror 6 according to FIG. 4 has an un-tilted array arrangement of the individual mirrors 21 relative to the xy-coordinate system.The individual group mirrors 21 Gi( i=1 to 18) are again emphasized in FIG. 4. In the arrangement according to FIG. 4 as well, some potential individual sensor mirrors 21 S and their field heights x i( i=1 to 9) are again emphasized.FIG. 5 shows a typical occupancy of an embodiment of the field facet mirror 6 with individual mirror groups 26 with respective group boundaries 27. It is illustrated in FIG. 5 that sensor individual mirrors 21 S are respectively present between two individual mirror groups 26 adjacent in one of the columns at each of the field heights x 1 to x 9 which do not belong to any of the individual mirror groups 26. A corresponding occupancy analogous to FIG. 5 results in an arrangement of the individual mirrors 21 tilted with respect to the xy-coordinate axes according to FIG. 3.FIG. 6 shows, in a perspective, schematic view, principal components of the illumination optical unit 11 on the one hand and of an intensity sensor device 31 for measuring a dependence of an intensity of the illumination light 3 impinging on the object field 8 on the detection object field coordinate x on the other hand. The intensity sensor device 31 includes selected individual sensor mirrors 21 Si from potential individual sensor mirrors 21s, which result from individual mirrors 21 of the field facet mirror 6 that cannot be used for the individual mirror groups 26, as already explained above with reference to FIGS. 3 to 5. Furthermore, the intensity sensor device 31 includes a plurality of intensity sensors 32 1 to 32 9, which are arranged in the form of a sensor line 33 spatially adjacent to the individual mirrors 34 of the second facet mirror 7. Compared to individual mirrors 34 of the second facet mirror 34, the intensity sensors 32 i are illustrated in exaggerated size in FIG. 6. The intensity sensors 32 i correspond in terms of shape and area to the second facets 25. This achieves the effect that the light loss by overradiation of the second facets 25 is similarly high as that by overradiation of the intensity sensors 32 i and thus the sensor signal remains proportional to the intensity in the object field 8, even if the light loss is variable over time, for example by a drifting source plasma.If the second facets 25 are not physical facets of fixed size, but rather virtual facets in the form of groups of second individual mirrors 34, the second facets 25 will have different shapes and sizes depending on the application. In this case, the intensity sensors 32 i may also have a variable size. This can be achieved by a larger number of sensors of different sizes, additional diaphragms in front of the sensors or by pixelated sensors, which are only partially read out.FIG. 6 illustrates a light path of the illumination light 3 which is guided from the light source 2 or the intermediate focus 5 avia one of the individual sensor mirrors 21 s, namely a sensor mirror of the type 21 S1 toward the associated intensity sensor 32 1.A corresponding guidance of an illumination light partial beam 3 1 from the light source 2 or the intermediate focus 5 avia the individual mirror group 26 1 and the second facet 25 1 toward the object field 8 is also schematically indicated.Highlighted by corresponding hatchings in FIG. 6 are two individual mirror groups 26 1 and 26 2 in the manner of the individual mirror groups 26 according to FIGS. 4 and 5, which are imaged in the object field 8 in a manner overlapping one another via associated second facets 25 1, 252. In the embodiment shown, the second facets 25 i each consist of a 2x2 array of the individual mirrors 34 of the second facet mirror 7. in practice, a second facet 25 i can also consist of exactly one individual mirror 34 or else be constructed from a different number of the individual mirrors 34, for example as a 3x3, as a 4x4, as a 5x5 array, as a 6x6 array or else as a 7x7 array.As in the case of the single mirror group 26 according to FIGS. 4 and 5, in the case of the illumination optical unit 11 according to FIG. 6, the single mirror groups 26 there, which are imaged in the object field 8 in a manner overlapping one another, are exactly nine single mirrors 21 wide in the x direction. These nine individual mirrors 21 are assigned to the field heights x 1 to x 9. Each of the individual mirror groups 26 thus comprises individual mirrors 21 from nine individual mirror columns 1 to 9 lying next to one another. Corresponding to this nine-column subdivision of the individual mirror groups 26 and the following field height assignment, the result is a typing of the individual sensor mirrors 21 S1 to 21 S9. selected for acting on the intensity sensors 32 1 to 32 9.The sensor individual mirrors of the type 21 S1 are individual mirrors 21 which are arranged in the same column as the individual mirrors 21 are arranged in the first, left column of the respective individual mirror group 26. The sensor individual mirrors of the type 21 S1 therefore belong to the field height x 1.Accordingly, the further types of sensor individual mirrors 21 belong in S2, 21S3,... to individual mirrors 21 of the field facet mirror 6, which are arranged in the same columns as the individual mirrors 21 in the second, third,... These further individual sensor mirrors of types 21 S2, 21S3,... thus belong to the field heights X 2, X 3,...This nine-column subdivision of the individual mirror groups 26 and of the individual sensor mirrors 21 Si enables spatial resolution of a measurement of the dependence of the intensity of the illumination light 3 impinging on the object field 8 into nine field height sections x 1 to x 9 between a left edge x l and a right edge x r of the object field 8. Due to the imaging, an image reversal results in the overlapping imaging of the individual mirror groups 26 into the object field 8, so that the object field 8 in FIG. 6 appears curved in the opposite direction compared to the individual mirror groups 26.The intensity sensors 32 i are arranged within the sensor row 33 in the order of their assignment to the types 21 Si of the individual sensor mirrors. This row sequence of the intensity sensors 32 i is not obligatory, but rather it is merely necessary to know the assignment of the intensity sensors 32 i to the types of the individual sensor mirrors 21 Si that is to say to the field height sections x 1 to x 9 which can be measured in each case by means of them.By means of the sensor individual mirrors of the type 21 S1 and the associated intensity sensor 32 1 it is thus possible to determine a measure for the intensity of the field height section x 1 of the detection object field coordinate x arranged on the left. The same applies to the individual sensor mirrors of types 21 S2 to 21 S9 and the intensity sensors 32 2 to 32 9. then assigned to the field height sections x 2 to x 9. With the aid of the entire sensor row 33, the intensity sensors 32 of which i receive the illumination light 3 of the respective types 21 Si the detection object field coordinate x can thus be measured over the entire object field 8 with respect to the illumination light intensity impinging there in each case.FIG. 7 shows an association correlation of the individual mirror groups 26 i to individual mirror columns on the field facet mirror 6; FIG. 7 shows the case, which differs from the schematic arrangement according to FIGS. 5 and 6, in that a total of 8 columns of individual mirror groups 26 ij( j=1 to 8) are arranged on the facet mirror 6. The illustration shows the dependence of a number N G of the individual mirror groups 26 ij on a location coordinate x of the field facet mirror 6.FIG. 8 shows, for the case of a field facet mirror 6 having a very much larger number of individual mirrors 21, which differs from the schematic illustration according to FIGS. 3 to 6, a distribution of potential sensor individual mirrors 21 sover an entire mirror surface of the first facet mirror 6. A selection of potential sensor individual mirrors 21 S for specific x-field positions is illustrated, namely for a total of five exemplary x-field positions (left field edge (x=x 1), field center (x=0), right field edge (x=x r) and still two x positions between the left field edge and the center (x=x 1 / 2) and between the center and the right field edge (x=x r / 2)).With regard to the large number of individual mirror groups 26 ij a distribution of the potential individual sensor mirrors 21 S according to FIG. 8 results in a good statistical distribution of individual sensor mirrors 21 Si. usable for the intensity device 31. For each of these individual sensor mirrors 21 s, the assignment of the adjacent individual mirrors 21 of the field facet mirror 6 to the respective individual mirror groups 26 results in ij, for which x-coordinate the respective individual sensor mirror 21 S is representative during the illumination of the object field 8 by the individual mirror groups 26 ij adjacent to these individual sensor mirrors 21 Si. Accordingly, the respective single sensor mirror 21 S can be assigned to one of the single sensor mirror types 21 Si, for example the types 21 S1 to 21 S9 explained above in connection with FIG. 6.Depending on the achievable spatial resolution via the potential individual sensor mirrors 21 S the number of intensity sensors 32 i of the intensity sensor device 31 can also be smaller or larger. This number i may be in the range between 3 and 100.FIGS. 9 to 11 illustrate a measurement precision of the intensity sensor device 31 in the case of an illumination light intensity strongly dependent on the detection object field coordinate x.FIG. 9 shows, by way of example, in dashed lines, a desired setpoint intensity distribution I SOLL, which is constant over the complete x-coordinate of the object field. An exemplary actual intensity distribution l IST is shown in full in FIG. 9, which has a cosine distribution by way of example over the x-coordinate of the object field 8 and is likewise greater (more intensive) by approximately 10% than the intensity I SOLL by way of example in the region of the maxima and is smaller (less intensive) by approximately 10% than the intensity I SOLL. in the region of the cosine minimum.FIG. 10 shows dashed correction measurement results I K in which intensity sensors 32 i( i=1 to 9) assigned to the respective x-coordinate of the object field 8, that is to say intensity sensors 32 assigned to the respective field height, for the constant illumination intensity distribution I SOLL according to FIG. 9 ; the x-positions which the respective intensity sensors 32 i measure on the basis of the assignment to corresponding individual sensor mirrors 21 Si are indicated in FIG. 10 on the x-axis with the numerals "1" to "9". The dashed, measured correction intensity profile I K of the intensity sensors 32 i over the x coordinate is not constant, unlike the constant illumination intensity I SOLL over this object field coordinate x. This corresponds to practice that a cumulative intensity application or a number of the different types 21 Si, to 21 S9 does not have to be constant. In the case of a realistic case illustrated in FIG. 10, for example, relatively few individual sensor mirrors of types 21 S1, 21S7 and 21 S9 are present, so that the intensity values measured there are comparatively small compared to the other measured values. These dashed correction measurement values I K in FIG. 10 serve as a calibration curve of the intensity sensor device 31 This calibration curve can be determined, for example, by measuring a projection exposure apparatus in which it is ensured in another way that the object field 8 is illuminated with a homogeneous illumination intensity distribution in accordance with the distribution I SOLL.FIG. 10 shows full lines of the measured value I M of the intensity sensors 32 1 to 32 9 for the illumination intensity profile I IST according to FIG. 9. A comparison of the dashed curve with the solid curve in FIG. 10 reveals, even without calculation of the relative changes, that the actual intensity distribution I IST is less illumination-intensive in the region of the central x coordinates than the desired distribution I SOLL and more intensive in the region of the left and right x coordinate edges.FIG. 11 shows a ratio formation of the measured values I M and I K drawn in full and dashed lines in FIG. 10 as a solid ratio measurement result I ISTM that is to say the measured values I M shown in full and normalized to the dashed correction values I K in FIG. 10 ; in comparison thereto, the actual illumination intensity distribution I IST over the detection object field coordinate x is again shown in dashed lines in FIG. 11, that is to say in principle the same curve which was shown in full line in FIG. 9. In contrast to FIG. 9, the illumination intensity distribution I IST is reproduced in FIG. 11 as a ratio value to the setpoint intensity distribution I SOLL.The vertical axis in FIG. 11 thus represents the ratio I M / I K or I IST / I SOLL respectively.FIG. 11 shows the good correspondence between the measured actual value I ISTM and the actual value I IST of the illumination intensity distribution over the detection object field coordinate x of the object field 8.A deviation between these two curves I IST and I ISTM can be at most in the range of 3%, in the range of 2.5%, in the range of 2%, or even smaller.In addition, as illustrated in FIG. 8, the sensor individual mirrors 21 scan be selected such that they cover the useful range of the illumination light far field in the two far field dimensions x and y over the entire field facet mirror 6.Due to this covering of the useful range of the illumination light far field in the two far field dimensions x and y by the arrangement of the usable sensor individual mirrors 21 s, the far field of the light source in the arrangement plane of the field facet mirror 6 can be completely measured in two dimensions x and y by means of a corresponding embodiment of the intensity sensor device 31. Such an embodiment of the intensity sensor device 31 then has a larger number of intensity sensors 32 ji, which cover the two-dimensionality of the far-field measurement. Such an intensity sensor device can have intensity sensors 32 ij for example, which are arranged in an array with j rows and i columns. Since, as already explained above in connection with the sensor row 33, only the assignment of the positions of the respective individual sensor mirrors 21 S to the respective intensity sensors 32 ij has to be known, an array arrangement of the intensity sensors 32 ij does not have to correspond to the arrangement of the individual sensor mirrors 21 S used for measurement.When measuring the dependence of the intensity of the illumination light 3 impinging on the object field 8 on the detection object field coordinate x, the individual mirrors 21 of the first facet mirror 6 of the illumination optical unit 11 are firstly assigned to the individual mirror groups 26 i of the first facet mirror 6 to the second facets 25 i of the second facet mirror 7, which second facets image these individual mirror groups 26 i at least in partial fields of the object field 8.Individual mirrors 21 of the first facet mirror 6 are then selected, which are not used in this assignment. These selected unused individual mirrors 21 are selected as the sensor individual mirror 21 S of the intensity sensor device 31.Subsequently, a coordinate assignment of the selected individual sensor mirrors 21s to the respective detection object field coordinate x i, is carried out, in which individual mirrors 21 of the first facet mirror 6 directly adjacent to the individual sensor mirrors 21s to be assigned are mapped into the object field 8. This corresponds to an assignment of the respective sensor individual mirror 21 sto a sensor individual mirror type 21 Si, as explained above.An assignment is now carried out, depending on the coordinate assignment carried out, of in each case one of the intensity sensors 32 i to the individual sensor mirror 32 Si. assigned to the respective detection object field coordinate x i.Now, a part of the illumination light 3 is guided as detection illumination light via the individual sensor mirror 21 assigned to the respective detection object field coordinate or the field height section x i Si to the assigned intensity sensor 32 i. This can be done parallel to the projection exposure. Sensor data of the intensity sensors 32 i acted upon by the detection illumination light are now evaluated in order to determine the dependence of the intensity I ist of the illumination light 3 impinging on the object field 8 on the at least one detection object field coordinate x.This sensor data evaluation can be followed by a correction of the intensity dependence of the illumination intensity on the detection object field coordinate x, for example by modifying an assignment of an assignment of the individual mirrors 21 of the first facet mirror 6 to the respective individual mirror groups 26 i or by modifying an assignment of the individual mirror groups 26 i to the second facets 25 i.The projection exposure can be carried out parallel to the measurement or else after a corresponding correction.The selection and assignment of the individual sensor mirrors 21 sand an evaluation of the sensor data can be carried out in such a way that a 2D far-field measurement results from the evaluated sensor data. The respective data of the selected and assigned individual sensor mirrors 21 scan form interpolation points of a far-range measurement field, between which points a conclusion is then drawn by extrapolation to the entire far-range measurement field.In order to produce a microstructured component, in particular a highly integrated semiconductor component, for example a memory chip, with the aid of the projection exposure apparatus 1, the reticle 12 and the wafer 19 are first provided. A structure on the reticle 12 is then illuminated with the illumination light 3 by the illumination optical unit 11 and projected onto a light-sensitive layer on the wafer 19 by the projection optical unit of the projection exposure apparatus 1. By developing the light-sensitive layer, a microstructure is then produced on the wafer 19 and the micro- or nanostructured component is produced therefrom.The component produced can be a microchip, in particular a memory chip.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2015 208 512 A1

[0002] EP 0 952 491 A2

[0009] WO 2010 / 099 807

[0038] US 2006 / 0132747 A1

[0044]

Claims

Illumination optical unit (11) - having a first facet mirror (6) with first individual mirrors (21) for the reflective guidance of illumination light (3) of an EUV light source (2) and for arrangement in a useful region of an illumination light far field, - having a second facet mirror (7) for the reflective guidance of the illumination light (3) reflected by the first facet mirror (6) towards an object field (8) in which an object (12) to be illuminated can be arranged, wherein the second facet mirror (7) has second individual mirrors (34) which form second facets (25) which, via partial beams (3 i) of the illumination light (3), image individual mirror groups (26) of the first facet mirror (6) which form first facets, at least in partial fields of the object field (8), an intensity sensor device (31) for measuring a dependence of an intensity (I IST) of the illumination light (3) impinging on the object field (8) on at least one detection object field coordinate (x), wherein the intensity sensor device (31) has: - a plurality of the first individual mirrors which represent sensor individual mirrors (21s) of the first facet mirror (6), wherein the sensor individual mirrors (21s) are assigned to a plurality of different object field positions (x i) along the detection object field coordinate (x), - a plurality of intensity sensors (32 i), wherein the sensor individual mirrors (21s) are designed for the reflective guidance of the illumination light (3) towards the intensity sensors (32 i).Illumination optical unit according to Claim 1, characterized in that the number of intensity sensors (32 i) is in the range between 3 and 100.Illumination optical unit according to Claim 1 or 2, characterized in that the intensity sensors (32 are arranged in i) spatially adjacent to the second individual mirrors (34) of the second facet mirror (7).Illumination optical unit according to one of Claims 1 to 3, characterized in that the intensity sensors (32 are arranged in i) as a sensor row (33).Illumination optical system according to one of Claims 1 to 4, characterized in that the individual sensor mirrors (21s) are arranged on the first facet mirror (6) in such a way that they cover the useful range of the illumination light far field in two far field dimensions (x, y).Method for measuring a dependence of an intensity (I IST) of the illumination light (3) impinging on the object field (8) on at least one detection object field coordinate (x) using an illumination optical unit (11) according to one of Claims 1 to 5, having the following steps: - assigning the individual mirrors (21) of the first facet mirror (6) of the illumination optical unit (11) to the individual mirror groups (26 i) of the first facet mirror (6) which form the first facets, to the second facets (25 i) of the second facet mirror (7) which image these individual mirror groups (26 i) at least in partial fields of the object field (8), selecting individual mirrors (21) of the first facet mirror (6) which are not used in the assignment as sensor individual mirrors (21s) of the intensity sensor device (31), - assigning the selected sensor individual mirrors (21s) to detection object field coordinates (x i), in which individual mirrors (21) of the first facet mirror (6) which are directly adjacent to the sensor individual mirrors (21s) are mapped into the object field (8), - assigning the sensor, depending on the assignment of the coordinates, each of the intensity sensors (32 i) to the individual sensor mirror (21s) assigned to the respective detection object field coordinate (x), and guiding detection illumination light (3) via the individual sensor mirror (21s) assigned to the respective detection object field coordinate (x i) to the assigned intensity sensor (32 i), - evaluating sensor data of the intensity sensors (32 i) acted upon by the detection illumination light (3) for determining the dependence of the intensity (I IST) of the illumination light (3) impinging on the object field (8) on the at least one detection object field coordinate (x).Method according to Claim 6, characterized byselecting and associating the individual sensor mirrors (21s) and evaluating the sensor data in such a way that the evaluated sensor data result in a 2D far-field measurement of the illumination light far field.Illumination system having an illumination optical unit (11) according to one of Claims 1 to 5 and having an EUV light source (2).Optical system having an illumination optical unit (11) according to one of Claims 1 to 5 and having a projection optical unit (10) for imaging the object field (8) into an image field (17).Projection exposure apparatus having an optical system according to Claim 9 and having an EUV light source (2).Method for producing a micro / or nanostructured component, having the following method steps: - provision of a reticle (12), - provision of a wafer (19) with a coating sensitive to the illumination light (3), - projection of at least one section of the reticle (12) onto the wafer (19) with the aid of the illumination exposure apparatus (1) according to Claim 10, - development of the light-sensitive layer exposed to the illumination light (3) on the wafer (19).Component produced by a method according to Claim 11.

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