METHOD AND ADJUSTING SYSTEM FOR ADJUSTING THE POSITION OF A FACET MIRROR OF A LITHOGRAPHING PLANT

Abstract

Method for adjusting the position of a first faceted mirror (20, 22) of a lithography system (1) along a predetermined direction, comprising: Measuring (S1) in the reticulum plane (6) of field positions corresponding to a selection of facets (21, 23) of a second facet mirror (20, 22) with visible light, wherein the visible light is directed onto the first facet mirror (20, 22), from it onto the second facet mirror (20, 22) and from it into the reticulum plane (6) and produces an image there based on the selection of the facets (21, 23) of the second facet mirror (20, 22), and wherein the field positions are measured based on the image; Calculating (S2) a position of the first facet mirror (20, 22) along the predetermined direction based on the measured field positions; Determine (S3) an adjustment value to adjust the position of the first faceted mirror (20, 22) along the predetermined direction based on the calculated position; and Adjusting (S4) the position of the first faceted mirror (20, 22) by the adjustment value.

Description

[0001] The present invention relates to a method for adjusting a position of a facet mirror of a lithography system and a system for adjusting the position of the facet mirror.

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system equipped with an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example, a silicon wafer, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] Driven by the pursuit of ever smaller structures in the production of integrated circuits, EUV lithography systems are currently being developed that use light with a wavelength in the range of 0.1 nm to 30 nm, particularly 13.5 nm. Since most materials absorb light at this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the refractive optics, i.e., lenses, as was previously the case.

[0004] Facet mirrors (e.g., field facet mirrors) can be used as mirrors, which comprise a large number of individual facets. To ensure consistent quality standards, EUV lithography system modules, especially facet mirrors, are calibrated for their positions before use (exposure process).

[0005] The calibration (also called adjustment) of EUV illumination systems consists of several steps, as explained below using the following examples. In a first step, the modules themselves are adjusted, which in the case of facet mirrors primarily concerns the adjustment of the facets to each other and to a support of the respective facet mirror. The fully adjusted modules are then integrated into the lithography system. The system adjustment is carried out geometrically, initially using coordinate measuring machines (CMMs) for rough adjustment (as described in WO 2019 / 002082 A1), then with visible light for fine adjustment, before the measurement of energetic quantities is carried out in a final step (acceptance step).

[0006] However, during the calibration of a facet mirror or module in particular using a coordinate measuring machine, uncertainties can sometimes arise. This is because, on the one hand, the support rings used to carry the facets have certain tolerances, and on the other hand, the actual optical surface is determined by the surface of the facets and not by the surface of the support on which the reference surface for the measurement is located. This primarily affects the position of the optical surface along the optical axis. The modules are then adjusted so that the field position and the angle of incidence of the illumination system are correctly adjusted, but the illumination system is sensitive to changes during use by the customer. For example, changes in uniformity or targeted improvements in homogeneity can result in field-dependent telecentricity errors. It is desirable to make the optical system more robust against such changes.

[0007] First, one can directly probe the facets to determine their (Z) position along the optical axis. However, since gaps between facets are typically in the low millimeter range, probing the side surfaces of the facets is usually difficult or even impossible.

[0008] There's also a risk of misaligning the bevel due to the force of the probe on the side surface. Furthermore, a tactile approach directly on the optical surface is rather disadvantageous because it could damage the optical surface.

[0009] The problem arises, among other things, from the fact that there are multiple mechanical interfaces between the optical surface on the facet and the reference surface on the mirror module. Due to the complexity of the design, the accumulation of tolerances along these interfaces ("mechanical tolerance chain") is comparatively long and therefore difficult to optimize. Tightening all specifications to these interface tolerances can prevent the system from becoming out of tolerance. However, the specifications required for this are difficult or inconsistent to achieve with currently known processes, so the yield of usable parts is unacceptable.

[0010] DE 10 2019 210 092 A1 and DE 10 2017 219 179 B3 each disclose methods for restoring an illumination system for an EUV system, in the course of which the positions of facet mirrors within the illumination system are adjusted.

[0011] Against this background, it is an object of the present invention to provide an improved adjustment of a position of a facet mirror of a lithography system.

[0012] According to a first aspect, a method for adjusting a position of a first facet mirror of a lithography system along a predetermined direction is provided. The method comprises: Measuring, in the reticle plane, field positions associated with a selection of facets of a second facet mirror with visible light; Calculating a position of the first facet mirror along the predetermined direction based on the measured field positions; Determining an adjustment value for adjusting the position of the first facet mirror along the predetermined direction based on the calculated position; and

[0013] Adjust the position of the first facet mirror by the adjustment value.

[0014] The inventors have surprisingly discovered that measuring all field positions is not necessary; simply measuring those field positions associated with a selection of facets of the second facet mirror is sufficient. This advantageously accelerates the adjustment of the position of the field facet mirror.

[0015] The first and second mirrors are arranged one behind the other in the beam path; the reticle follows them. The order of the first and second mirrors in the beam path is interchangeable (first first, then second mirror, or vice versa). The first and second facet mirrors can in particular be components of an illumination system of a lithography system. For example, one of the first and second facet mirrors is a field facet mirror and the other is a pupil facet mirror. In particular, the first facet mirror can be a pupil facet mirror and the second facet mirror a field facet mirror, or conversely, the first facet mirror can be a field facet mirror and the second facet mirror a pupil facet mirror. The projection exposure system can be an EUV lithography system.EUV stands for "Extreme Ultraviolet" and refers to a wavelength of working light between 0.1 nm and 30 nm. The projection exposure system can also be a DUV lithography system. DUV stands for "Deep Ultraviolet" and refers to a wavelength of working light between 30 nm and 250 nm.

[0016] "Field positions assigned to a selection of facets of a second facet mirror" here means that the field positions are mapped to the field plane or object plane using the selection of facets. The selection can refer to facets in the field plane, i.e., facets of a field facet mirror, or in the pupil plane, i.e., facets of a pupil facet mirror.

[0017] The facets can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partially circular edge contour. The facets can be designed as flat facets or, alternatively, as convex or concave curved facets. The first or second facet mirror comprises, in particular, more than 100, preferably more than 1000 facets.

[0018] The field positions are measured, for example, using optical wavelengths that do not necessarily correspond to the useful wavelength of the lithography system, for example with visible light. The field position can also be referred to as the field position. In general, the terms “position” and “position” are used synonymously. The field position refers in particular to a position of the illumination field (in particular the light distribution with which the first and / or second facet mirror is illuminated) in the exit plane (in particular the field plane or object plane). When measuring the field positions, in particular the lateral position (X and Y position) of the respective selected facets with respect to the imaging optics (reference) is measured, particularly because the position in the direction of the optical axis (Z position) is usually not clearly defined or difficult to measure.

[0019] The field positions of the facet selection (facet selection) can be used to determine the position of the entire facet mirror. In particular, the overall position of the facet mirror is determined from the mean field position of all measured facet selection field positions or from the difference between the mean field positions of several facet selection zones, which are explained in more detail below. The position of the facet mirror specifically refers to the mean position of all facets of the facet mirror and thus also of the facet mirror itself.

[0020] Based on the calculated position of the facet mirror, the adjustment value can be determined, which indicates in which direction along the predetermined direction and how far the facet mirror should be moved. For this purpose, for example, a known relationship between the position of the facet mirror and an acceptance size to be optimized (this is a specification from the customer, i.e., the purchaser of the lithography system, which is a prerequisite for proper acceptance) of the optical system is used. The acceptance size can be a size that is changed when the homogeneity is changed by the user of the lithography system. By optimizing the acceptance size, a change in the acceptance size when the homogeneity is changed by the user of the lithography system is reduced.

[0021] When adjusting the position of the facet mirror, the facet mirror is moved by the amount specified in the adjustment value and in the direction specified by the adjustment value. For adjustment, for example, a spacer can be inserted or removed to change the position of the facet mirror support and thus the entire facet mirror.

[0022] The described adjustment strategy can be used to support mechanical position determination via coordinate measuring machines, improve accuracy, and potentially even replace coordinate measuring machine measurements, provided that the mechanical interfaces allow direct access to the optical measuring range. This can also eliminate the need for larger coordinate measuring machines in larger system geometries. Furthermore, the accuracy of system qualification is increased while simultaneously maintaining the accuracy of the adjustment runtime, or if other measurement steps are eliminated, it can even be shortened.

[0023] According to one embodiment, the adjustment value is further determined based on the sensitivity of a physical property of the lithography system to changes in the position of the first facet mirror. The position of the facet mirror is further adjusted in such a way that the sensitivity and / or the physical property is optimized.

[0024] The physical property (particularly the attenuation size) can, for example, be crosstalk or an influence on the telecentricity of the illumination system. This crosstalk occurs particularly when there is an error in the Z-position of the facet mirror. Crosstalk specifically describes a change in the telecentricity of the illumination system depending on the setting of insert diaphragms, which are arranged after the reticle and can be pushed into the illumination field on one side for light correction. This crosstalk describes a parasitic change in the illumination pupil when attempting to correct the illumination field for homogeneity.

[0025] Sensitivity refers to the sensitivity of the channel position to a decentration and / or tilt of the facet mirror. Decentering refers specifically to a translational movement, and tilting refers specifically to a rotation. The sensitivities exhibit a systematic progression (e.g., described by a polynomial) across the pupil facet mirror. Because the insert diaphragms for intensity correction are only inserted into the light field on one side, this creates an energetic asymmetry in the pupil and thus a telecentricity error.

[0026] The adjustment is advantageously carried out in such a way that this telecentricity error is reduced. For this purpose, a previously known relationship between the sensitivity and the position of the facet mirror along the predetermined direction is used to determine the adjustment value accordingly. The adjustment value is determined in such a way that the reduction magnitude is reduced. This means, for example, that the telecentricity error is reduced in the event of decentering and / or tilting of the facet mirror.

[0027] According to a further embodiment, the physical property is a telecentricity error.

[0028] According to a further embodiment, the field positions of the selection of facets are measured using an illumination setting which is stored on a data storage device of the lithography system.

[0029] The existing illumination setting is, in particular, a setting that can actually be used for illumination during operation of the lithography system. This is advantageous in that an existing function of the illumination system can be used for adjustment, and no additional function is required.

[0030] In particular, an existing illumination setting is selected that particularly involves the channels with high sensitivity. This allows the measurement of the field positions of the facet selection based on the existing illumination setting to reflect a measurement of the field positions of all facets.

[0031] According to a further embodiment, the selection of facets takes place in a first and a second zone of the second facet mirror, wherein the first and second zones are arranged axially symmetrically to one another.

[0032] The first and second zones can each have an elongated, for example, elliptical shape. The zones are specifically chosen to reflect the positions of all facets.

[0033] According to a further embodiment, one of the first and second facet mirrors is a pupil facet mirror, wherein the first and second zones are provided at opposite poles of the pupil facet mirror.

[0034] According to a further embodiment, calculating the position of the first facet mirror comprises calculating a difference between the respective positions of the field positions assigned to the first zone and the respective positions of the field positions assigned to the second zone.

[0035] If the mean field position is calculated across all channels, the errors of the channels in the first zone cancel each other out when the first facet mirror is moved along the predetermined direction. However, if the mean field position of the channels in the first zone and the channels in the second zone are determined separately, and the difference between the separately determined mean values ​​is calculated, the Z-position of the facet mirror can be determined.

[0036] According to a further embodiment, the selection of facets comprises less than a quarter, in particular less than a sixth, of all facets of the second facet mirror.

[0037] This significantly accelerates the measurement of field positions and thus the adjustment of the facet mirror position. However, the selection of facets should also include at least one-twentieth or one-tenth of all facets to provide a representative image of all facets and / or to obtain sufficient light for the field position measurement.

[0038] According to a further embodiment, the predetermined direction runs along the optical axis of the first facet mirror.

[0039] According to a second aspect, an adjustment system is provided for adjusting a position of a first facet mirror of a lithography system, in particular by carrying out the above method, wherein the adjustment system comprises: a measuring device for measuring field positions in the reticle plane, wherein the field positions are assigned to a selection of facets of a second facet mirror, with visible light; a computing device for calculating a position of the field facet mirror along the predetermined direction based on the measured field positions, and for determining an adjustment value for adjusting the position of the field facet mirror along the predetermined direction based on the calculated position; and an adjustment device for adjusting the position of the field facet mirror by the adjustment value.

[0040] The embodiments and features described for the method apply accordingly to the proposed adjustment system and vice versa.

[0041] The adjustment described above refers to the specific adjustment of a (first) facet mirror. However, an analogous adjustment of other optical elements of a lithography system or another optical system is also conceivable. Thus, instead of the facet mirror, the adjustment of a general mirror module can also be performed. In particular, the method of the first aspect and the adjustment system of the second aspect can be used generally to adjust the position of an actuator with high sensitivity to a desired size. For example, the described method and adjustment system can be used to adjust a system with ten mirrors arranged one behind the other.

[0042] A generalization of the previously described procedure can be described as follows: Measuring a measured quantity with high sensitivity to the reference quantity to be adjusted; Determination of the deviation of the actual state from a target state of the acceptance variable to be adjusted based on the measured variable (particularly taking into account the sensitivity of the measured variable to the acceptance variable); and Adjustment of the actuator based on the determined deviation.

[0043] "One" in this case is not necessarily limited to a single element. Rather, multiple elements, such as two, three, or more, may also be included. Any other counting term used here should not be understood as implying a limitation to the exact number of elements stated. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

[0044] Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0045] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the accompanying figures. Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography; Fig. 2 shows an example of a facet with an adjustment pin; Fig. 3 shows an example of the sensitivity of the channel layers to a decentration of a facet mirror along a Z-direction; Fig. 4 shows a method for adjusting a position of a facet mirror; Fig. 5 shows an example of a field position measurement of all facets; Fig. 6 shows another example of a field position measurement of all facets; Fig. 7 shows an example of a field position measurement with an existing lighting setting; Fig. Figure 8 shows a relationship between telecentricity and distance between the mean field positions of both zones; Fig. 9 shows an adjustment system for adjusting a position of a facet mirror; Fig. 10 shows an example of a process for adjusting the position of the facet mirror; and Fig. Figure 11 shows an example of a generalization of the adjustment strategy for difficult-to-access sample sizes.

[0046] In the figures, identical or functionally equivalent elements are provided with the same reference numerals unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0047] Fig. 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optics 4 for illuminating an object field 5 in an object plane 6 (here also referred to as the "reticle plane"). In an alternative embodiment, the light source 3 can also be provided as a separate module from the remaining illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0048] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced via a reticle displacement drive 9, in particular in a scanning direction.

[0049] In the Fig. For illustrative purposes, Figure 1 shows a Cartesian coordinate system with an x-direction x, a y-direction y, and a z-direction z. The x-direction x runs perpendicular to the plane of the drawing. The y-direction y runs horizontally, and the z-direction z runs vertically. The scanning direction runs in the Fig. 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0050] The projection exposure system 1 comprises a projection optics 10. The projection optics 10 serves to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0051] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the image plane 12 in the region of the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular along the y-direction y, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0052] The light source 3 is an EUV radiation source. The light source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation 16 has, in particular, a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. The light source 3 can be a free-electron laser (FEL).

[0053] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 at grazing incidence (GI), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector 17 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0054] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics 4.

[0055] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6 as the field plane, it is also referred to as a facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as facets. Of these first facets 21, Fig. 1 only some examples are shown.

[0056] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partially circular edge contour. The first facets 21 can be designed as flat facets or, alternatively, as convexly or concavely curved facets.

[0057] As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 themselves can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can, in particular, be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

[0058] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0059] In the beam path of the illumination optics 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978 B1.

[0060] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets. In the example described below (see in particular Fig. 4) The facet mirror 22 is adjusted as the "first facet mirror." Alternatively, however, the facet mirror 20 can also be adjusted as the "first facet mirror."

[0061] The second facets 23 can also be macroscopic facets, which can, for example, be round, rectangular, or hexagonal, or alternatively facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0062] The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces.

[0063] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a fly's-eye integrator.

[0064] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

[0065] With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0066] In a further embodiment of the illumination optics 4 (not shown), a transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which transmission optics contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GI mirrors, grazing incidence mirrors).

[0067] The illumination optics 4 has in the version shown in the Fig. 1, after the collector 17 there are exactly three mirrors, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

[0068] In a further embodiment of the illumination optics 4, the deflection mirror 19 can also be omitted, so that the illumination optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

[0069] The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optics into the object plane 6 is usually only an approximate imaging.

[0070] The projection optics 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0071] In the Fig. In the example shown in Figure 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 are also possible. The projection optics 10 is a doubly obscured optic. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0072] Reflection surfaces of the mirrors Mi can be designed as freeform surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one rotational symmetry axis of the reflection surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0073] The projection optics 10 has a large object-image offset in the y-direction y between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction y can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0074] The projection optics 10 can, in particular, be anamorphic. It has, in particular, different magnifications βx, βy in the x and y directions x, y. The two magnifications Bx, By of the projection optics 10 are preferably (Bx, By) = (+ / -0.25, + / -0.125). A positive magnification β means imaging without image inversion. A negative sign for the magnification B means imaging with image inversion.

[0075] The projection optics 10 thus leads to a reduction in the ratio 4:1 in the x-direction x, i.e. in the direction perpendicular to the scanning direction.

[0076] The projection optics 10 leads to a reduction of 8:1 in the y-direction y, i.e. in the scanning direction.

[0077] Other magnifications are also possible. Magnifications with the same sign and absolutely identical in the x and y directions (x, y), for example, with absolute values ​​of 0.125 or 0.25, are also possible.

[0078] The number of intermediate image planes in the x- and y-directions x, y in the beam path between the object field 5 and the image field 11 can be the same or can be different, depending on the design of the projection optics 10. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions x, y are known from US 2018 / 0074303 A1.

[0079] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form a respective illumination channel for illuminating the object field 5. This can, in particular, result in illumination according to the Köhler principle. The far field is divided into a plurality of object fields 5 using the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to them.

[0080] The first facets 21 are each imaged onto the reticle 7 by an associated second facet 23, superimposed on one another, to illuminate the object field 5. The illumination of the object field 5 is, in particular, as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0081] By arranging the second facets 23, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. By selecting the illumination channels, in particular the subset of the second facets 23 that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil fill.

[0082] A likewise preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

[0083] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics 10 are described below.

[0084] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0085] The entrance pupil of the projection optics 10 cannot usually be precisely illuminated with the second facet mirror 22. When imaging the projection optics 10, which images the center of the second facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found in which the pairwise determined distance of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

[0086] The projection optics 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. This optical element can be used to account for the different positions of the tangential entrance pupil and the sagittal entrance pupil.

[0087] In the Fig. In the arrangement of the components of the illumination optics 4 shown in Figure 1, the second facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The first facet mirror 20 is arranged tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the second facet mirror 22.

[0088] The Fig. 2 shows an example of a facet system 100 with a facet 102. The facet 102 can correspond to the previously described first or second facet 21, 23 (here in the example a pupil facet 23). The facet 102 has an optical surface 104 onto which light is incident and reflected during operation of the lithography system 1. The facet 102 is elongated and is fastened via a first nut 106 to an adjustment pin 108, which extends along the elongated extension direction of the facet 102 and projects into it. The adjustment pin 108 serves to adjust a position of the facet 102, in particular along a Z-direction, which runs along an optical axis of the facet 102 and perpendicular to the optical surface 104. The Z-direction is the predetermined direction. The Fig. The directions X, Y and Z described in 2 to 12 do not correspond to the directions x, y and z from the Fig. 1.

[0089] At one end of the alignment pin 108 that does not extend into the facet 102, the alignment pin 108 is connected to an optional cooling unit 114 via a second nut 110. The cooling unit 104 has a surface 112 that serves to cool the facet 102. Furthermore, the cooling unit 104 forms a reference surface for the relative positioning of the optical surface 104.

[0090] In order to solve the problem described in the introduction and, for example, to make the facet mirror 22 more robust against changes in homogeneity (although the method described here is equally applicable to the positioning of the facet mirror 20), it is important to know the precise position of the facet mirror 20, 22. Since there are several mechanical interfaces between the optical surface 104 on the facet 102 and the reference surface 114 on the mirror module, an accumulation of tolerances occurs along these interfaces ("mechanical tolerance chain"). Due to the complexity of the structure, this tolerance chain is comparatively long and therefore difficult to optimize. Tightening all specifications to these interface tolerances can prevent the system from going out of tolerance. However, the specifications required for this cannot be stably achieved with currently known processes.

[0091] Therefore, adjusting the tolerances is not sufficient to determine the position of the facet mirror 22 and the position of the facet mirror 22 must be determined empirically.

[0092] Such an empirical determination of the position of the facet mirror 22 is carried out using the Fig. 3 to 11.

[0093] An error in the Z position of the facet mirror 22 (i.e., the error in the position of the mirror 22 along the Z direction) creates, among other things, crosstalk on the telecentricity of the illumination system 2. This crosstalk describes a change in the telecentricity of the system 2 depending on the setting of insert diaphragms arranged after the reticle 7 and which can be pushed into the illumination field on one side for light correction. This crosstalk describes a parasitic change in the illumination pupil when attempting to correct the illumination field for homogeneity. To minimize these side effects, the position of each individual illumination channel, particularly along a y-axis, in the reticle plane 6 is optimized during system design. This optimization leads, among other things, to the individual channels of the illumination system 2 no longer superimposing perfectly, as this would in turn be detrimental to the crosstalk.Sensitivities arise from this imperfect superposition.

[0094] The Fig. Figure 3 shows an example of a systematic sensitivity of channel positions to a decentration of the facet mirror 22 along the Z-direction. In other words, the Fig. 3 an effect of a displacement of the facet mirror 22 by 1 mm along the Z direction on the Y position of the individual images of the facets 23 in the reticle plane 6.

[0095] The facets 23 corresponding to the channels are arranged in the facet mirror 22 at positions which are in the Fig. 3 are indicated by the horizontal and vertical axes, wherein the horizontal axis indicates a position of the facets 23 along an X-direction and the vertical axis indicates a position of the facets 23 along the Y-direction. The center of the facet mirror 22 corresponds in Fig. 3 of the position X = 0 mm and Y = 0 mm. The X and Y directions are lateral directions perpendicular to the optical axis Z.

[0096] In the Fig. 3, the channels corresponding to the individual facets 23 are represented by "+", "o", and "-". The symbols "+", "o", and "-" indicate a sensitivity of the respective channel positions to a displacement of the facet mirror 20, 22 along the Z direction. The symbol "+" indicates that a displacement of the facet mirror 22 by 1 in an arbitrary unit length along the positive Z direction displaces the corresponding facet 23 by 0.5 [arbitrary unit length] in the positive Y direction. The symbol "o" indicates that a displacement of the facet mirror 22 by 1 [arbitrary unit length] along the positive Z direction displaces the corresponding facet 23 by 0 [arbitrary unit length] in the Y direction.The symbol “-” indicates that a displacement of the facet mirror 22 by 1 [arbitrary unit of length] along the positive Z direction displaces the corresponding facet 23 by 0.5 [arbitrary unit of length] in the positive Y direction (corresponding to 0.5 [arbitrary unit of length] in the negative Y direction).

[0097] The Fig. Figure 3 shows a pronounced shift in the sensitivity of the channel positions when the facet mirror 22 is decentered in the Z direction. This means that when the facet mirror 22 is misaligned along the positive Z direction (+Z), the channels located in the upper part of the pupil of the facet mirror 22 are mostly shifted along the positive y direction (+Y) relative to their individual target positions, while the channels in the lower half of the pupil are mostly shifted along the negative y direction (-Y) relative to their individual target positions. Because the insert diaphragms are only pushed into the light field on one side for intensity correction, this creates an energetic asymmetry in the pupil and thus a telecentricity error.

[0098] At the Fig. 3 are systematic sensitivities and not actual field positions of the individual facets 23. If the actual field position of the individual channels is measured in relation to the target position, images such as in Fig. 5 and Fig. 6. In the Fig. 5 and Fig. 6 corresponds to the representation of facets 23 of the Fig. 3. Furthermore, the provisions of the Fig. 5 and Fig. 6 used characters “+”, “o” and “-” which are from the Fig. 3.

[0099] In the Fig. 5 shows that the deviation of the actual position from the specified position does not exhibit any systematic dependence on the position of the facet 23 in the illumination pupil, because it is a well-adjusted system. This can be recognized by a uniform distribution of the signs "+", "o" and "-" in the Fig. 5. In contrast, Fig. 6 Acceptance data of a system 2, which shows significantly increased values ​​regarding crosstalk, which violate the specification. However, this system 2 can be adjusted back to the specification if one uses the Fig. 3, a correction of the Z-position of the facet mirror 20, 22 (adjustment value) is calculated. Fig. In the example shown in Figure 6, the required correction would be ΔZ = -0.200 [any length unit] (adjustment value).

[0100] To perform the described correction, the position errors of the individual channels in the reticle plane with respect to their position in the pupil are required. This measurement is time-consuming. However, there is a way to significantly accelerate the measurement. This option is described with reference to the Fig. 4 described.

[0101] The Fig. Figure 4 shows a method for adjusting the position of the (pupil) facet mirror 22 (in other embodiments, however, it could also be the (field) facet mirror 20). The adjusted facet mirror 22 (or 20) is the first facet mirror. In a step S1, field positions associated with a selection of facets 21 of the facet mirror 20 are measured using visible light.

[0102] Since the sensitivity to the position of the facet mirror 22 in the Z-direction is relatively large and at the same time has a simple describable course ( Fig. 3), it is not necessary to evaluate all channels individually. Instead, it is sufficient to collect the data in groups. This corresponds to the measurement of field positions, which is assigned to the selection of facets 21.

[0103] To measure the field positions of the facet selection, it is advisable to choose an existing illumination setting (for example, one stored on a data storage device of the lithography system) in which the channels with high sensitivity are particularly involved. In the present example (see sensitivities of the Fig. 3 and field location of the Fig. 6) these are the channels that are “above” and “below” in the pupil (above and below refer to the representations of the Fig. 2, Fig. 5, Fig. 6 and Fig. 7).

[0104] The existing lighting setting that comes closest to these requirements is in the Fig. 7. In the lighting setting of the Fig. 7, only approximately one-eighth of all facets 21 are illuminated. This facet selection is formed by facets 21 of a first zone 116 ("top"), which has an elliptical shape adjacent to a first pole 118. The facet selection is further formed by facets 21 of a second zone 120 ("bottom"), which has an elliptical shape adjacent to a second pole 122. The two zones 116, 120 are arranged mirror-symmetrically with respect to an axis of symmetry 124. The axis of symmetry 124 is a cross-section of the facet mirror 20, 22, which runs along the position Y = 0 [arbitrary unit of length]. The zones 116, 120 can also be referred to as a monopole.

[0105] In a step S2 of the Fig. 4, a position of the facet mirror 22 along the Z-direction is calculated. This calculation is carried out taking into account the measured field positions of the facet selection, which are shown in the Fig. 7 is shown.

[0106] If you look at the mean field position over all the Fig. 7 illuminated channels, then when the facet mirror 22 is moved along the Z-axis, the errors of the channels of the first zone 116 cancel each other out with the errors of the channels of the second zone 120. However, if the mean field position of the channels of the first zone 116 and that of the channels of the second zone 120 are determined separately, the Z-position of the facet mirror 22 can be determined from this.

[0107] In a step S3 of the Fig. 4, an adjustment value for adjusting the position of the facet mirror 22 along the Z-direction is determined. For this purpose, the position of the facet mirror 22 calculated in step S2 and the systematic sensitivity from the Fig. 3. In the example of Fig. 7 results in an adjustment value, i.e. a required correction of the position of the facet mirror 22 along the Z direction at ΔZ = -0.200 [arbitrary unit of length].

[0108] In a step S4 of the Fig. 4, the position of the facet mirror 20 is adjusted along the Z direction according to the adjustment value. For this purpose, the support of the facet mirror 20 is adjusted by removing a corresponding spacer element with a height of 0.200 [any unit of length] along the Z direction.

[0109] The Fig. Figure 8 shows the crosstalk to the telecentricity (vertical axis) as a function of the distance between the center field positions of the two zones 116, 120 (horizontal axis). The first curve 126 refers to the first zone 116, and the second curve 128 refers to the second zone 120.

[0110] The system is in the Fig. 8 is clearly visible, and both curves 126 and 128 have a linear progression. This confirms that there is indeed a proportionality between the field position and the target variable (crosstalk).

[0111] The Fig. 9 shows an adjustment system 200 for adjusting a position of the facet mirror 22 (here in the example). The adjustment system 200 is suitable for the method of Fig. 4. For this purpose, the adjustment system 200 comprises a measuring device 202, a computing device 204 and an adjustment device 206, which are each connected to one another via a communication channel 208 and can exchange data.

[0112] The measuring device 202 is suitable for measuring the field positions associated with the selection of facets 21 (here in the example) with visible light (step S1 of the Fig. 4). The computing device 204 is adapted to calculate a position of the facet mirror 22 along the predetermined direction based on the measured field positions of the selection of facets 21 (step S2 of Fig. 4), and to determine the adjustment value for adjusting the position of the facet mirror 22 along the predetermined direction based on the calculated position of the facet mirror 22 (step S3 of Fig. 4). The adjustment device 206 is configured to adjust the position of the facet mirror 22 by the adjustment value.

[0113] The Fig. 10 shows another example of a process for adjusting the position of the facet mirror 22.

[0114] In step S5, the field position of zones 116, 120 (monopoles) is measured. Step S5 corresponds to step S1 from the Fig. 4. In a step S6, the Fig. 7 is obtained. In a step S7, the crosstalk is determined based on the relationship from step S6 and the measurement from step S5. Step S7 may replace steps S2 and S3 of the Fig. 4 in whole or in part.

[0115] In a step S8, the position of the facet mirror 22 is determined. This can be done as before in step S2 of the Fig. 4. In a step S9, the sensitivity of the position of the facet mirror 22 to crosstalk, as it is determined from the Fig. 3 is known. Based on the crosstalk determined in step S7, the position of the facet mirror 22 determined in step S8 and the sensitivity from step S9, the position of the facet mirror 22 is adjusted in a step S10 (corresponding to step S4 of the Fig. 4). Step S11 describes an optional iterative adjustment and a repetition of steps S5 - S7.

[0116] The Fig. Figure 11 shows an example of a generalization of the adjustment strategy for difficult-to-access sample sizes. Fig. The adjustment described in Figures 3 to 10 refers to the specific adjustment of a facet mirror 22. However, an analogous adjustment of other optical elements of the lithography system or of another optical system is also conceivable. Thus, instead of the facet mirror 20, 22, the adjustment of a general mirror module can also be carried out. In particular, the method of Fig. 4 generally used to adjust the position of an actuator with high sensitivity to a desired value to be adjusted.

[0117] Such a generalization of the procedure of Fig. 4 and Fig. 10 is in the Fig. 11 and can be described as follows. In a step S12, a measurement variable with high sensitivity to the acceptance variable to be adjusted is measured. This can be done, for example, optically, as in steps S1 and S5. In a step S13 of the Fig. 11, an indication of the sensitivity of the measured variable to the decrease variable, i.e. a relationship between the measured variable and the decrease variable, is obtained. In a step S14 of the Fig. 11, based on the relationship between step S13 and the measurement of step S12, a deviation between the actual state (as measured in step S12) and the target state of the reduction size is determined.

[0118] In a step S15 of the Fig. 11, the position of the actuator for adjusting the position of the optical system to be calibrated is determined. In a step S16 of the Fig. 11, the sensitivity of the actuator to the reduction size is obtained. Based on the deviation determined in step S14, the position of the actuator determined in step S15, and the sensitivity from step S16, the position of the actuator is adjusted in step S17 to adjust a corresponding optical surface. Step S18 of the Fig. 11 describes an optional iterative adjustment and a repetition of steps S12 - S17.

[0119] Although the present invention has been described using exemplary embodiments, it is amenable to numerous modifications. The optical system can, for example, also be used in a DUV lithography system. In particular, the above statements apply to pupil facet mirrors or, in general, to any faceted mirror.

[0120] The Fig. Figure 3 only shows the sensitivities of the channel positions to the Z-decentration, but similar systematic sensitivities also arise for X- and Y-decentrations and X-, Y- and Z-rotations. For these systematic sensitivity curves, an adjustment of the position of the facet mirror can also be carried out using the method of Fig. 4, which serves to reduce crosstalk. LIST OF REFERENCE SYMBOLS 1 projection exposure system 2 Lighting system 3 Light source 4 Lighting optics 5 Object field 6 Object plane or reticle plane 7 reticles 8 reticle holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer holders 15 Wafer relocation drive 16 Illumination radiation 17 Collector 18 Intermediate focal plane 19 Deflecting mirrors 20 first facet mirror 21 first facet 22 second facet mirror 23 second facet 100 facet system 102 facets 104 optical surface 106 first mother 108 Adjustment pin 110 second mother 112 Surface 114 Cooling unit 116 first zone 118 first pole 120 second zone 122 second pole 124 axis of symmetry 126 first curve 128 second curve 200 adjustment system 202 Measuring device 204 Computing device 206 Adjustment device 208 Communication channel M1 mirror M2 mirror M3 mirror M4 mirror M5 mirror M6 mirror S1 - S18 Process steps

Claims

[1] Method for adjusting a position of a first facet mirror (20, 22) of a lithography system (1) along a predetermined direction, comprising: Measuring (S1), in the reticle plane (6), field positions associated with a selection of facets (21, 23) of a second facet mirror (20, 22) with visible light, wherein the visible light is radiated onto the first facet mirror (20, 22), from there onto the second facet mirror (20, 22) and from there into the reticle plane (6) and there generates an image based on the selection of the facets (21, 23) of the second facet mirror (20, 22), and wherein the field positions are measured based on the image; Calculating (S2) a position of the first facet mirror (20, 22) along the predetermined direction based on the measured field positions; Determining (S3) an adjustment value for adjusting the position of the first facet mirror (20, 22) along the predetermined direction based on the calculated position; and Adjusting (S4) the position of the first facet mirror (20, 22) by the adjustment value. [2] The method according to claim 1, wherein the adjustment value is further determined based on a sensitivity of a physical property of the lithography system to changes in the position of the first facet mirror (20, 22). [3] The method of claim 2, wherein the physical property is a telecentricity error. [4] Method according to one of claims 1 to 3, wherein the measurement of the field positions of the selection of facets (21, 23) is carried out on the basis of an illumination setting which is stored on a data memory of the lithography system. [5] Method according to one of claims 1 to 4, wherein the selection of facets (21, 23) takes place in a first and a second zone (116, 120) of the second facet mirror (20, 22), wherein the first and second zones (116, 120) are arranged axially symmetrically to one another. [6] The method of claim 5, wherein one of the first and second facet mirrors is a pupil facet mirror, the first and second zones (116, 120) being provided at opposite poles (118, 122) of the pupil facet mirror (20, 22). [7] The method according to claim 5 or 6, wherein calculating the position of the first facet mirror (20, 22) comprises calculating a difference between the respective positions of the field positions (21, 23) associated with the first zone (116) and the respective positions of the field positions associated with the second zone (120). [8] Method according to one of claims 1 to 7, wherein the selection of facets (21, 23) forms less than a quarter, in particular less than a sixth, of all facets (21, 23) of the second facet mirror (20, 22). [9] Method according to one of claims 1 to 8, wherein the predetermined direction runs along the optical axis of the first facet mirror (20, 22). [10] Adjustment system (200) for adjusting a position of a first facet mirror (20, 22) of a lithography system (1), in particular by carrying out the method according to one of claims 1 to 9, wherein the adjustment system comprises: a measuring device (202) for measuring field positions in the reticle plane (6), wherein the field positions are assigned to a selection of facets (21, 23) of a second facet mirror (20, 22), with visible light, wherein the visible light is radiated onto the first facet mirror (20, 22), from there onto the second facet mirror (20, 22) and from there into the reticle plane (6) and there generates an image based on the selection of the facets (21, 23) of the second facet mirror (20, 22), and wherein the field positions are measured based on the image; a computing device (204) for calculating a position of the field facet mirror (20, 22) along the predetermined direction based on the measured field positions, and for determining an adjustment value for adjusting the position of the field facet mirror (20, 22) along the predetermined direction based on the calculated position; and an adjustment device (206) for adjusting the position of the field facet mirror (20, 22) by the adjustment value.

Images