Individual mirror of pupil facet mirror and pupil facet mirror for illumination optical unit of projection exposure apparatus

Abstract

An individual mirror (11) of a pupil facet mirror (10) of an illumination optical unit (25) of a projection exposure apparatus (1) is mounted so as to be pivotable about two pivot axes (31, 32), with the ratio of pivotability of the individual mirror (11) about the two pivot axes (31, 32) being at least 2: 1.

Description

[0001] The content of German patent application DE 10 2022 209 214.7 is incorporated herein by reference. Technical Field

[0002] The invention relates to individual mirrors of a pupil facet mirror and to a pupil facet mirror for an illumination optical unit of a projection exposure apparatus. The invention also relates to an illumination optical unit, an illumination system, an optical system and a projection exposure apparatus having such a pupil facet mirror. The invention also relates to a method for producing a microstructured or nanostructured device and to a device produced according to the method. Finally, the invention relates to a method for calibrating the pivoting of individual mirrors. Background Art

[0003] Illumination optical units for projection exposure apparatuses are known, for example, from DE 10 2018 214 223 A1, US Pat. No. 6,658,084 B2 and US Pat. No. 9,063,336 B2.

[0004] For various reasons, it may be desirable to make individual mirrors of a pupil facet mirror (also referred to as pupil facets) displaceable, in particular pivotable. However, the practical implementation of switchable pupil facets is a technically very challenging task. Therefore, there is a continuing need to improve pupil facets, in particular with regard to their switchability. Summary of the invention

[0005] This object is achieved by the subject matter of the present invention.

[0006] The essence of the invention is that the individual mirrors of the pupil facet mirror are pivotable, wherein the ratio of the pivotability about two transversely, in particular vertically extending pivot axes is at least 2:1, in particular at least 3:1, in particular at least 5:1, in particular at least 10:1, in particular at least 20:1, in particular at least 30:1, in particular at least 50: 1. The ratio of the pivotability of the individual mirrors about the two pivot axes can in particular correspond approximately to the aspect ratio of the object field of the projection exposure apparatus and / or to the aspect ratio of the individual field facets.

[0007] The pivotability of the individual mirrors can in particular be anisotropic. In particular, the pivotability in a first direction can be greater than the pivotability in a second direction, which is different from the first direction, in particular perpendicular to the first direction.

[0008] By reducing the pivotability of the individual mirrors relative to at least one of the two pivot axes, the effort required for a stable and precise positioning of the individual mirrors can be reduced. Furthermore, different aspects of the bearing of the individual mirrors can be improved.

[0009] Without limiting the generality, the reflective surface of the individual reflectors may be polygonal, in particular quadrilateral, in particular rectangular, non-square or square, hexagonal or circular, in particular circular.

[0010] In particular, the reflective surface may have a 2nd and / or 3rd order rotational symmetry.

[0011] The order of the rotational symmetry of the reflective surface may in particular differ from the order of the rotational symmetry of the pivotability of the individual reflectors. In particular, it may differ from the order of the rotational symmetry of the configuration of the pivot axis of the individual reflectors.

[0012] The individual reflectors can have the same size but different pivotability regions, in particular in a direction perpendicular to the pivot axis. It has been shown that this can improve, in particular simplify, the positioning of the individual reflectors.

[0013] The use of individual mirrors for pupil facet mirrors should not be understood restrictively. Corresponding individual mirrors can also be used in field facet mirrors or in another facet mirror. They can generally be used in multi-mirror modules, in particular MEMS modules. The following description applies accordingly to such uses.

[0014] The diameter of the reflective surface, without limiting its generality, in particular the inner diameter, may be in the range of 1 mm to 20 mm. In particular, the diameter may be at most 10 mm. In particular, the diameter may be at least 2 mm, in particular at least 3 mm. For example, the diameter may be about 6 mm.

[0015] According to one aspect, the larger of the two pivotable areas is at most + / - 50 mrad, in particular at most + / - 30 mrad, in particular at most + / - 15 mrad, in particular at most + / - 5 mrad, in particular at most + / - 3 mrad. In particular, it can also have at least corresponding values.

[0016] According to one aspect, the smaller of the two pivotable areas is at most + / - 25 mrad, in particular at most + / - 15 mrad, in particular at most + / - 10 mrad, in particular at most + / - 5 mrad, in particular at most + / - 5 mrad, in particular at most + / - 3 mrad, in particular at most + / - 2 mrad, in particular at most + / - 1 mrad, in particular at most + / - 0.5 mrad, in particular at most + / - 0.2 mrad and in particular at most + / - 0.1 mrad.

[0017] It is therefore approximately one order of magnitude smaller than the pivotable area of ​​known active pupil facets.

[0018] It can be seen that the advantages resulting from the displaceability of the pupil facets, in particular the increase in the average illuminator efficiency, can also be achieved in large components with a reduced pivotable area.

[0019] In a conventional compound eye concentrator with static pupil facets, each pupil facet is assigned to exactly one field facet as part of the channel assignment. The surface (normal and radius of curvature) of the pupil facet is therefore chosen and configured such that it images the field facet assigned to it into the object field. A plurality of pupil facets can form a group, with the pupil facets of one of the groups being assigned to the same field facet (see US 6,658,084 B2). Since the pupil facets are static, this assignment cannot be changed after manufacture and assembly.

[0020] In this case, the field facets can be active, i.e. displaceable. They can be switched from one pupil facet to another. However, at a fixed time, the field facets illuminate only a single pupil facet. Therefore, only pupil facets from different groups can illuminate simultaneously, i.e. contribute to the illumination of the object field. Pupil facets from the same group cannot illuminate simultaneously. Therefore, the desired illumination settings (settings for short) must already be known during the design of the illuminator (illumination optical unit). The grouping of pupil facets is then optimized for these settings, thereby achieving the highest possible illuminator efficiency for these settings. Other settings are generally no longer able to operate at full illuminator efficiency.

[0021] The illuminator efficiency of a setting is calculated as the ratio of the number of emitted pupil facets to the number of existing field facets. If each pupil facet group is queried at least once in the setting, this corresponds to an illuminator efficiency of 100%. If a specific group is not queried in the setting, the illuminator efficiency is reduced accordingly.

[0022] In addition, there are two types of pupil filling degrees among the characteristics of the illumination optical unit.

[0023] The set pupil filling degree is provided by the ratio of the set queried number of pupil facets to the total number of available pupil facets.

[0024] System pupil filling is the ratio of the total number of field facets present to the total number of pupil facets present.

[0025] The illuminator efficiency is usually a function of the set pupil filling degree of the illumination system. When using static pupil facets, an average illuminator efficiency of about 67% can be achieved at a system pupil filling degree of 20% and a set pupil filling degree of 20%. This is because at the 20% setting, in typical cases, many pupil facet groups are queried multiple times, while other groups are not queried at all. This mutual blocking of pupil facets is also called setting conflict. By switchable, i.e. pivotable, embodiments of the pupil facets, such setting conflicts can be reduced, in particular completely avoided. In the case of switchable pupil facets, individual pupil facets can only guide the light of individual field facets to the mask master at any fixed time, but can be pivoted in such a way that it guides the illumination radiation from a specific field facet to the mask master at one time and guides the illumination radiation from another field facet to the mask master at another time. Setting conflicts can be particularly resolved by switching the query pupil facet that is switched to the used field facet to the unused field facet. If the switchable pupil facets can cover the entire field facet module, all conceivable settings can also be supported.

[0026] Surprisingly, it could be shown that the average illuminator efficiency can be significantly increased if the pupil facets do not cover the entire field facet module, but instead only a few field facets, in particular two, three, four or five field facets, can be controlled.

[0027] In particular, it can be shown that the advantages resulting from the switchability of the pupil facets can also be achieved to a large extent by reducing the switching range (displaceable area). In this way, the design effort can be reduced. In addition, different aspects of the bearing can be improved, in particular its thermal conductivity.

[0028] It has also been found that the effort required for a stable and precise displacement of the pupil facets can be further reduced if the field facets and / or the object field in fact generally have an elongated shape, in particular with an aspect ratio of at least 5:1, in particular at least 10:1, for example 13:1.

[0029] According to a further aspect, the smaller of the two pivotable areas can be at most + / - 2 mrad, in particular at most + / - 1 mrad, in particular at most + / - 0.5 mrad.

[0030] In this case, the larger of the two pivotable areas may represent the pivotability within the plane of the pupil facet module about an axis perpendicular to the scanning direction.

[0031] The smaller of the two pivotable areas can exhibit pivotability within the plane of the pupil facet module about a second axis perpendicular to the first axis, ie parallel to the scanning direction.

[0032] Reference here to the scanning direction is to be understood as meaning that the individual mirrors in the illumination optical unit are in each case arranged such that a pivoting thereof about an axis oriented perpendicular to the scanning direction results in a displacement of the illumination radiation in the object field parallel to the scanning direction, or a pivoting thereof about an axis oriented parallel to the scanning direction results in a displacement of the illumination radiation in the object field perpendicular to the scanning direction.

[0033] Since the required switching range of the pupil facets in the scanning direction is very small, the switching range is almost one-dimensional. It has been found that this can be used to simplify the bearings of the pupil facets and / or the actuation of their displaceability and / or the sensor arrangement for detecting their displacement position, in particular without which there would be a significant loss of quality.

[0034] Different aspects that result from this and that can bring benefits individually or in combination are described below.

[0035] According to an aspect, the bearing of the pupil facet may comprise a flexure, in particular a universal joint.

[0036] According to another aspect, the bearings for the individual mirrors for each pivoting degree of freedom comprise one or more leaf springs, wherein the leaf springs for one pivoting degree of freedom are thicker and / or stiffer than the leaf springs for another pivoting degree of freedom.

[0037] It has been found that reducing the pivotable area by a factor x at a known actuation force results in a corresponding increase in the stiffness of the leaf spring or generally the universal joint in this direction.

[0038] As a result, the natural frequency of the tilt mode increases by a factor of √x. This is beneficial for the stability of the pivot in this direction against mechanical vibrations.

[0039] Furthermore, the possibility of using thicker leaf springs leads to a lower thermal resistance from the reflector to the reflector carrier, in particular to a lower x -1 / 3 This is advantageous for dissipating the heat power introduced into the individual mirrors by the illumination radiation, in particular by EUV radiation.

[0040] The natural frequency of the individual mirrors can be at least 300 Hz, in particular at least 500 Hz, in particular in one direction. In a direction perpendicular thereto, the natural frequency of the tilt mode of the individual mirrors can be in particular at least 1000 Hz, in particular at least 1500 Hz.

[0041] According to a further aspect, the bearings for the individual mirrors for one or two pivoting degrees of freedom have end stops for delimiting the pivotable area.

[0042] This can increase the precision of the pivotability.The end stops can be used to define particularly precise pivot positions.

[0043] Such end stops can also be used to calibrate the displacement position.

[0044] According to another aspect, at most one, in particular exactly one, of the pivoting movements about the two pivot axes is detected by the sensor device. In other words, the individual reflector can in particular have only a single sensor device for detecting a pivoting of the individual reflector only about one of the two pivot axes. The pivoting about the other of the two pivot axes can be performed without a sensor. In particular, the number of pivoting degrees of freedom detected by the sensor can be smaller than the number of pivoting degrees of freedom controllable by the actuator.

[0045] In this case, the pivoting movement about the pivot axis with the larger pivotable area is preferably detected by means of a sensor.

[0046] In particular, at most one, in particular exactly one, of the two pivoting movements can be controlled with a closed-loop control. The other pivoting movement, in particular the pivoting movement about the axis with a smaller pivotable area, can be controlled in particular without feedback. In particular for this pivoting movement, i.e. for the pivoting movement about the axis with a smaller pivotable area, an end stop can be provided for delimiting the pivotable area.

[0047] In principle, it is even possible to control both pivoting movements solely by open-loop control, ie without feedback.

[0048] This greatly simplifies the positioning and design of the individual reflectors.

[0049] According to a further aspect, a sensor arrangement having one or more eddy current sensors can be used to detect the pivot position of individual mirrors.

[0050] This allows for a particularly simple and stable sensor concept.

[0051] According to another aspect, the pivot axis and the flexure can be located in the same plane. In particular, the leaf spring for implementing the pivot axis can also be located in this plane.

[0052] This allows a particularly flat design. The flat design significantly simplifies the production of the flexure, in particular compared to flexure elements whose effective axis of rotation lies within the reflecting surface and whose leaf springs must therefore be configured as extending out of the plane.

[0053] According to a further aspect, the pivot axis can be spaced apart from the reflective surface. In particular, the pivot axis can be arranged behind or below the reflective surface of the pupil facet.

[0054] The fact that the tilt axis is located below the reflective mirror means that the reflective surface moves sideways during tilting. However, it has been shown that this is not a problem in the case of the small tilt angles mentioned above.

[0055] The pivot axis may be spaced apart from the reflecting surface, in particular by at least 1 mm, in particular by at least 2 mm, in particular by at least 3 mm in the direction of the mirror normal.

[0056] The distance of the pivot axis from the reflective surface in the direction of the surface normal of the reflective surface can in particular be at least one fifth of the reflector diameter, in particular at least one third of the reflector diameter, in particular at least half of the reflector diameter.

[0057] According to a further aspect, a reference position sensor may be provided for determining one or more reference signals for the pivot position of one or both pivot axes.

[0058] Incremental sensors such as encoders are often integrated as reference index sensors. The reference index sensor always points to the same increment, which is why the absolute position can also be reproduced very accurately with incremental encoders.

[0059] The reference position sensor does not need to be accurate over the entire measuring range, but only needs to be able to reproduce the reference position repeatably, which can be an advantage if this is easier to achieve under known boundary conditions.

[0060] The invention also relates to a pupil facet mirror for an illumination optics unit of a projection exposure apparatus, having a plurality of individual mirrors according to the preceding description.

[0061] The distance between adjacent individual reflectors may be at most 1 mm, in particular at most 500 μm, in particular at most 400 μm, in particular at most 300 μm. The distance here refers in particular to the gap width between adjacent individual reflectors, in particular to the minimum gap width between adjacent individual reflectors.

[0062] The invention also relates to an illumination optics unit for a projection exposure apparatus, comprising a field facet mirror with a plurality of field facets and a pupil facet mirror according to the preceding description, by means of which the field facets can be imaged onto an object field.

[0063] The advantages of the illumination optical unit according to the invention derive from what has been described above.

[0064] According to a further aspect, at least a subset of the pupil facets is displaceable, so that in each case the corresponding pupil facet can be assigned to exactly one or at least two, three, four or five different field facets.

[0065] This means that they can be positioned by means of the way in which they image the corresponding facets into the object field.

[0066] This subset may comprise at least 50% of the pupil facets, in particular at least 70% of the pupil facets, in particular at least 90% of the pupil facets, in particular all pupil facets of the pupil facet mirror.

[0067] In principle, different pupil facets with different pivotable areas can be formed. This can further increase the illuminator efficiency. At the same time, the advantages resulting from the lower displacement of the pupil facets can be at least partially achieved.

[0068] Individual mirrors of the pupil facet mirror may in particular be configured such that their pivotable area in the scanning direction is larger than their pivotable area in the cross-scanning direction.

[0069] One of the two pivot axes, in particular the pivot axis having the larger displacement area, can in particular be aligned perpendicularly to the scanning direction.

[0070] One of the two pivot axes, in particular the pivot axis having the smaller displacement area, can in particular be aligned perpendicularly to the cross-scanning direction.

[0071] The invention furthermore relates to an illumination system which, in addition to the above-described illumination optical unit, has a radiation source, in particular an EUV radiation source, for generating illumination radiation.

[0072] In addition to the above-described illumination optical unit, an optical system for a projection exposure apparatus also has a projection optical unit for imaging a reticle arranged in an object field into an image field.

[0073] The projection exposure apparatus according to the invention has an illumination optical unit according to the description above, a radiation source for generating illumination radiation, in particular in the EUV range, and a projection optical unit for imaging a reticle arranged in the object field into an image field.

[0074] The invention also relates to a configuration of individual mirrors according to the above in an illumination optical unit for a projection exposure device such that the pivot axis with the larger displacement area is aligned perpendicular to the scanning direction and the pivot axis with the smaller displacement area is aligned perpendicular to the cross scanning direction.

[0075] The invention also relates to a method for producing a microstructured or nanostructured device and a device produced according to the method. For this purpose, a projection exposure apparatus according to the above is provided and a structure on a reticle arranged in the object field is imaged onto a radiation-sensitive coating of a wafer arranged in the image field.

[0076] The invention also relates to a method for calibrating the pivoting of an individual reflector according to the above. For this purpose, the individual reflector is pivoted, in particular at a constant pivoting speed. Here, the back electromotive force distribution is determined. Here, the jump position in the back electromotive force distribution is determined. The calibration support point can then be determined based on the current value of the jump position.

[0077] In general, the current-angle characteristic can be determined.

[0078] According to one aspect, two calibration support points are determined for each pivoting degree of freedom, which can be used to determine the offset and / or gain correction.

[0079] A reference position sensor can also be used to determine the reference signal. In particular, this sensor can be arranged in the central area of ​​the pivoting area. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Further advantages and details of the present invention will become apparent from the description of exemplary embodiments with reference to the accompanying drawings, in which:

[0081] Figure 1 Schematically shows a meridional section of a microlithography projection exposure apparatus with respect to an illumination optical unit;

[0082] Figure 2 Show according to Figure 1 A plan view of a facet arrangement of a field facet reflector of an illumination optical unit of a projection exposure apparatus;

[0083] Figure 3 Show according to Figure 1 A plan view of a facet arrangement of a pupil facet mirror of an illumination optics unit of a projection exposure apparatus;

[0084] Figure 4 Shows similar Figure 2 A diagram of a facet configuration of another embodiment of a field facet reflector;

[0085] Figures 5 to 7 An exemplary illustration of an embodiment of a pupil facet mirror with a plurality of pupil facets (individual mirrors) is shown, wherein a perspective view with a stepped cross section ( Figure 5 )、Floor plan( Figure 6 ) and cross-section diagram ( Figure 7 );as well as

[0086] Figure 8 An exemplary diagram showing the tilting of pupil facets necessary for controlling three adjacent field facets. DETAILED DESCRIPTION

[0087] The microlithography projection exposure device 1 is used for manufacturing microstructured or nanostructured electronic semiconductor devices. The light source 2 emits EUV radiation for illumination, the wavelength of which is, for example, in the range of 5 nm to 30 nm. The light source 2 can be a GDPP (gas discharge produced plasma) source or an LPP (laser produced plasma) source. A synchrotron-based radiation source can also be used for the light source 2. A person skilled in the art will find information about such a light source, for example, in US 6,859,515 B2. EUV illumination light or illumination radiation 3 is used for illumination and imaging in the projection exposure device 1. The EUV illumination light 3 downstream of the light source 2 first passes through a concentrator 4, which can be, for example, a nested concentrator with a multi-shell structure known in the prior art, or alternatively an elliptical concentrator. A corresponding concentrator is known from EP 1 225 481 A2. Downstream of the concentrator 4, the EUV illumination light 3 first passes through an intermediate focal plane 5, which can be used to separate the EUV illumination light 3 from unwanted radiation or particle parts. After passing through the intermediate focal plane 5, the EUV illumination light 3 is first incident on the field facet mirror 6. The total beam of the illumination light 3 has a numerical aperture α in the intermediate focal plane 5.

[0088] In order to facilitate the description of the positional relationship, the Cartesian global xyz coordinate system is depicted in the accompanying drawings. Figure 1 In the diagram, the x-axis extends perpendicular to and out of the drawing. The y-axis Figure 1 The z-axis extends to the right. Figure 1 Extending upward.

[0089] In order to facilitate the description of the positional relationship of the various optical components of the projection exposure apparatus 1, a Cartesian local xyz or xy coordinate system is also used in the following figures. Unless otherwise described, the corresponding local xy coordinates span the corresponding main configuration plane of the optical component, such as a reflection plane. The x axes of the global xyz coordinate system and the local xyz or xy coordinate system are parallel to each other. The corresponding y axis of the local xyz coordinate system or xy coordinate system is at a certain angle relative to the y axis of the global xyz coordinate system, which angle corresponds to the tilt angle of the corresponding optical component around the x axis.

[0090] Figure 2 The facet configuration of the field facets 7 of the field facet mirror 6 is shown in an exemplary manner. The field facets 7 are rectangular and have the same x / y aspect ratio in each case. The x / y aspect ratio can be, for example, 12 / 5, can be 25 / 4 or can be 104 / 8.

[0091] The field facets 7 define the reflecting surface of the field facet reflector 6 and are grouped into four columns, each with six to eight field facet groups 8a, 8b. The field facet groups 8a each have seven field facets 7. Two additional peripheral field facet groups 8b of the two central field facet columns each have four field facets 7. The facet configuration of the field facet reflector 6 has gaps 9 between the two central facet columns and between the third and fourth facet rows, wherein the fixed spokes of the concentrator 4 shield the field facet reflector 6.

[0092] In a variant not shown here, the field facet mirror 6 is designed as a MEMS mirror array with a plurality of tiltable individual mirrors, from which each field facet 7 is formed. Such a configuration of a field facet mirror 6 is known from US 2011 / 0001947 A1.

[0093] By moving the individual mirrors perpendicularly to the mirror array configuration plane and tilting the individual mirrors accordingly, the radii of curvature of the group of individual mirrors of the field facets of the MEMS mirror array and the radii of curvature of the group of individual mirrors of the pupil facets of the MEMS mirror array can be adapted, as likewise described in US 2011 / 0001947 A1. It is also possible to adjust the radii of curvature by tilting the individual mirrors without a corresponding displacement perpendicularly to the mirror array configuration plane, effectively then producing, for example, a Fresnel mirror.

[0094] After being reflected by the field facet mirror 6 , the EUV illumination light 3 is divided into light beams or partial light beams assigned to the respective field facets 7 and incident on the pupil facet mirror 10 .

[0095] The field facets 7 of the field facet reflector 6 can be tilted between a plurality of illumination tilt positions, as a result of which the direction of the beam path of the illumination light 3 reflected by the respective field facet 7 is changed and thus the point of incidence of the reflected illumination light 3 on the pupil facet reflector 10 can be changed. Corresponding field facets displaceable between various illumination tilt positions are known from US 6,658,084 B2 and US 7,196,841 B2. This facilitates the specification of the illumination settings, i.e. the distribution of the illumination angles for illuminating the object field. Examples of illumination settings are known, in particular, from DE 10 2008 021 833 A1.

[0096] Figure 3An exemplary facet configuration of a circular pupil facet 11 of a pupil facet mirror 10 is shown. The pupil facets 11 are arranged around the center of a facet ring, which is located inside another facet ring. Other shapes and / or configurations of the pupil facets 11 are also possible. At least one pupil facet 11 is assigned to each partial beam of EUV illumination light 3 reflected by one of the field facets 7 in such a way that a respective impingement facet pairs an object field illumination channel which comprises one of the field facets 7 and one of the pupil facets 11 and predefines the relevant partial beam for EUV illumination light 3. The channel-by-channel assignment of the pupil facets 11 to the field facets 7 is performed based on the desired illumination of the projection exposure apparatus 1.

[0097] At least a subset of the pupil facets 11 can be switched between at least two illumination tilt positions by means of an associated actuator 12 . Figure 3 The actuator 12 is shown only schematically. The pupil facet 11 can be switched between two tilt positions, between three tilt positions, between four tilt positions, or even between a greater number of tilt positions. The pupil facet mirror 10 can have different types of pupil facets 11, which can be switched into a different number of illumination tilt positions.

[0098] The pupil facet mirror 10 may also have fixed pupil facets 11 which are designed to be fixed relative to a pupil facet carrier 13 of the pupil facet mirror 10 , ie not switchable between tilted positions.

[0099] A set of pupil facets 11 of a pupil facet reflector 10 is assigned to the field facet 7 via the corresponding illumination tilt position of the field facet 7. Each pupil facet 11 of one of these sets is irradiated by the illumination light 3 via exactly one of the different tilt positions of the relevant field facet 7, so that a specific illumination channel is formed between the field facet 7 and one of the pupil facets 11 of the pupil facet set according to the tilt position of the field facet 7. The illumination channels that can be used according to exactly one tilt position of the field facet 7 constitute an illumination channel group, that is, the pupil facets 11 in the set of pupil facets 11 assigned to the field facet 7 can be irradiated by the partial beams of illumination light via the field facet 7. The field facet 7 can have more tilt positions than those that lead to the formation of illumination channels, and these tilt positions can be set by actuators connected thereto. In the following, only the tilt positions that lead to the formation of illumination channels will be referred to as tilt positions.

[0100] Between the pupil facets 11 which may be present in the respective illumination channel and the subsequent illumination beam path of the partial beam of illumination light guided via this illumination channel, the direction of this beam path can be influenced by the respective illumination tilt position of the pupil facets 11. For example, in this way it is possible in each case to assign one and the same pupil facet 11 to different field facets 7 via one illumination channel, so that the pupil facets 11 can be assigned to different field facets 7 depending on their tilt position. On the other hand, the pupil facets 11 are fixed. F Assigned to at most one field plane 7, usually to exactly one field plane.

[0101] The field facet mirror 6 has several hundred field facets 7, for example 300 field facets 7. The number of pupil facets 11 of the pupil facet mirror 10 can be at least equal to the sum of the tilt positions of all field facets 7 of the field facet mirror 6. In this case, some pupil facets 11 will not be used for the assignment of the pupil facets used to the field facets. It may be particularly advantageous if the sum of the tilt positions of all field facets 7 of the field facet mirror 6 is equal to the number of pupil facets 11.

[0102] However, a number of pupil facets 11 guided by the sum of the tilt positions of all field facets 7 is not mandatory. Due to the switchability of the pupil facets 11, a number of pupil facets 11 can be configured for the pupil facet mirror 10, and the number of pupil facets 11 is less than the sum of the tilt positions of all field facets 7. For example, if each of the field facets 7 has two different tilt positions, the number of pupil facets 11 can also be as large as the number of field facets 7, which can be greater than 10%, greater than 20%, greater than 30%, greater than 40%, or greater than 50%. In this case, the number of pupil facets 11 may be less than 200% of the number of field facets 7, less than 190%, less than 180%, or less than 170%.

[0103] In a variant not shown, the pupil facet mirror 10 is constructed as a MEMS mirror array with a plurality of tiltable individual mirrors, in particular micromirrors, wherein each pupil facet 11 is formed by a plurality of such individual mirrors. Such a structure of a pupil facet mirror 10 is known from US 2011 / 0001947 A1.

[0104] By pupil facet mirror 10 (see Figure 1) and optionally a subsequent transfer optical unit 17 (constituted by three EUV mirrors 14, 15, 16) images the field facets 7 into an object plane 18 of the projection exposure apparatus 1. The EUV mirror 16 is embodied as a mirror for grazing incidence (grazing incidence mirror). Arranged in the object plane 18 is an object in the form of a reticle 19, wherein an illumination area in the form of an illumination field is illuminated with EUV illumination light 3, which coincides with an object field 20 of a downstream projection optical unit 21 of the projection exposure apparatus 1. The object field illumination channels are superimposed in the object field 20. The EUV illumination light 3 is reflected by the reticle 19.

[0105] The overall beam of illumination light 3 at the object field 20 has an object-side numerical aperture NA which may lie, for example, in the range between 0.04 and 0.15.

[0106] The projection optical unit 21 images the object field 20 in the object plane 18 into an image field 22 in an image plane 23. Arranged in the above-mentioned image plane 23 is a wafer 24 with a photosensitive layer, which is exposed during projection exposure using the projection exposure apparatus 1. During projection exposure, the reticle 19 and the wafer 24 are scanned in a synchronized manner in the y direction. The projection exposure apparatus 1 is embodied as a scanner. The scanning direction y is also referred to below as the object displacement direction.

[0107] The projection optical unit 21 has an imaging ratio β. For example, if the projection optical unit 21 reduces the object field 20 by 4 times and images it into the image field 22, the imaging ratio β is 1 / 4. For example, the imaging ratio range of the projection optical unit 21 can be between 1 / 2 and 1 / 16, such as 1 / 5, 1 / 6, 1 / 7 or 1 / 8.

[0108] In accordance with Figure 1 In mutually perpendicular planes xz, yz, the projection optical unit 21 can be designed in a deformable manner with different imaging ratios βx, βy. Examples of such deformable projection optical units are known from US Pat. No. 9,366,968 and US Pat. No. 9,983,484.

[0109] βx ranges from 1 / 3 to 1 / 5, especially in the region of 1 / 4; βy can range from 1 / 4 to 1 / 10, especially in the region of 1 / 8.

[0110] The field facet mirror 6, the pupil facet mirror 10 and optionally the mirrors 14 to 16 of the transmission optical unit 17 are components of an illumination optical unit 25 of the projection exposure apparatus 1. The transmission optical unit 17 can also be deformable. Figure 1In variants of the illumination optical unit 25 not shown in the figure, the transmission optical unit 17 can also be partially or completely omitted, so that no additional EUV mirror, exactly one additional EUV mirror, or exactly two additional EUV mirrors can be arranged between the pupil facet mirror 10 and the object field 20. The pupil facet mirror 10 can be arranged in the plane of the entrance pupil of the projection optical unit 21.

[0111] The illumination optical unit 25 together with the projection optical unit 21 forms an optical system of the projection exposure apparatus 1 .

[0112] The field facet mirror 6 represents a first facet mirror of the illumination optical unit 25 . The field facet 7 represents a first facet of the illumination optical unit 25 .

[0113] Pupil facet mirror 10 represents a second facet mirror of illumination optical unit 25 Pupil facet 11 represents a second facet of illumination optical unit 25 .

[0114] Figure 4 A further embodiment of the field facet reflector 6 is shown. Figure 2 Components corresponding to those explained in the field facet reflector 6 have the same reference numerals and only references which differ according to Figure 2 The scope of the components of the field facet mirror 6 is explained. Figure 4 The field facet reflector 6 has a field facet arrangement with arcuate field facets 7. These field facets 7 are arranged in a total of five columns, which in each case have a plurality of field facet groups 8. The field facet arrangement is inscribed in a circular boundary of a carrier plate 26 of the field facet reflector 6.

[0115] All field facets 7 are accommodated on a corresponding carrier plate 26 of the field facet mirror 6 within an area having the dimensions FFx, FFy. Figure 2 These dimensions FFx, FFy of the field facet reflector 6 used there are also highlighted in FIG. Figure 3 In FIG. 1 , the dimensions PFx, PFy of the surface, in which all pupil facets 11 are accommodated, are highlighted accordingly.

[0116] according to Figure 4 The field facets 7 in the embodiments have the same area and the same ratio of width in the x-direction to height in the y-direction, which corresponds to Figure 2 The x / y aspect ratio of the field facet 7 of an embodiment.

[0117] In the following content, refer to Figures 5 to 7 Further details of the pupil facet mirror 10 are described.

[0118] The pupil facet mirror 10 may have a densely packed array of pupil facets 11, such as Figures 5 to 7In the following description of the pupil facet mirror 10, the pupil facets 11 are also referred to as individual mirrors.

[0119] The pupil facets 11 are actuatable. They can be pivoted in particular about a first pivot axis 31 and a second pivot axis 32. The two pivot axes 31, 32 can in particular be perpendicular to each other. Each pupil facet 11 is mounted by means of a flexure 33. The flexure 33 is in particular a universal joint.

[0120] The two pivot axes 31 , 32 lie in particular in the plane of the flexure 33 .

[0121] The pivot axes 31, 32 are implemented as leaf springs. The leaf springs with which the pivot axes 31, 32 are realized are located in particular on the plane of the flexure 33. This enables a particularly flat design. In addition, this simplifies the manufacture of the flexure 33, in particular a flexure element that is located on the reflective surface with respect to the effective rotation axis.

[0122] The pivot axes 31, 32 are spaced apart from the reflective surface 34 of the individual reflectors. The pivot axes 31, 32 are located in particular below or behind the reflective surface 34.

[0123] Pupil facets 11 may have different pivotable areas, in particular for the two pivot axes 31, 32. In particular, their pivotable range in the direction perpendicular to the scanning direction (y direction) may be at most ±15 mrad, in particular ±5 mrad, in particular ±3 mrad.

[0124] In a direction perpendicular thereto, ie for a pivoting movement in the scanning direction, the pivotable area may be approximately one order of magnitude smaller. The pivotable area of ​​an individual mirror for a pivoting movement in the scanning direction may particularly be at most ±2 mrad, particularly ±1 mrad, particularly at most ±0.5 mrad.

[0125] The pivotable area can be determined particularly roughly by the pitch of the field facets 7 or the group of field facets 8 in the scanning direction or transversely, in particular perpendicularly, to the scanning direction. In particular, it can be a result of the ratio of the pitch to the distance between the field facet mirror 10 and the pupil facet mirror 10, in particular to the distance of the field facets 7 and the pupil facets 11 assigned to one another. In particular, the pitch here can denote the distance between corresponding points (e.g. a midpoint or two peripheral points) on adjacent field facets 7 or groups of field facets 8.

[0126] Different pivotable areas in the x and y directions can be achieved by suitable bearings of the individual mirrors. For example, the design of the flexure can be different for the two pivot axes 31, 32. In particular, leaf springs for differently mounted individual mirrors can be formed, in particular with different stiffnesses.

[0127] A stiffer spring can be thicker. A thicker design can reduce thermal resistance.

[0128] In particular, the bearings of the individual mirrors can be configured in such a way that the thermal resistance of the mechanical parts displaceable in one direction is at most half of the thermal resistance of the mechanical parts displaceable in the other direction. This can significantly reduce the overall thermal resistance of the bearing.

[0129] The reflective surface 34 can be approximately circular, in particular circular, or substantially hexagonal with rounded corners. Other shapes are also possible. The reflective surface can also be in particular square or rectangular with an aspect ratio of at least 1.1:1, in particular at least 1.2:1, in particular at least 1.5:1, in particular at least 2:1.

[0130] In each case the reflective surface 34 has an inner circle with a diameter d of 6 mm. Other dimensions are also possible.

[0131] It is also possible to form different pupil facets 11 having reflecting surfaces 34 of different shapes and / or sizes.

[0132] The individual mirrors of the pupil facet mirror 10 are in each case spaced apart. In the neutral position of the individual mirrors, a gap 35 remains between two adjacent individual mirrors. The nominal width of the gap 35 may be 400 μm.

[0133] In the exemplary embodiment shown by way of example, the distance between the pivot axes 31 , 32 and the reflective surface 34 is 3 mm.

[0134] The pivoting movement of the individual mirrors is 5 mrad, resulting in a lateral deflection of the mirror profile of approximately 15 µm.

[0135] Some details of the actuatability of the pupil facets 11 are described below.

[0136] An actuating device is provided for the displacement of the individual reflectors. The actuating device comprises an actuating pin 36. The actuating pin is connected to a reflector body 37 of the individual reflector in a power-transmitting manner.

[0137] The actuating device further comprises an annular back iron 48 .

[0138] The annular back iron 48 forms a bridge made of a ferromagnetic material suitable for guiding magnetic flux.

[0139] The actuating device further comprises end stops 38 , 39 for one or both pivoting directions.

[0140] The end stop 38 is designed as a displaceable inner ring.

[0141] The end stop 39 is designed to fix the outer ring. The inner ring can in particular be arranged inside the outer ring.

[0142] The actuating device may have a pair of pole shoes 40 , 41 for each pivoting direction.

[0143] Furthermore, the actuating device has a drive magnet in the form of a permanent magnet 42 .

[0144] Furthermore, the actuating device comprises a pair of coils 43 , 44 for each pivot axis 31 , 32 .

[0145] A soft iron core 45 may be disposed inside each coil 43 , 44 .

[0146] Furthermore, the actuating device comprises a yoke element 46. The yoke element 46 is arranged on the respective side of the coils 43, 44 relative to the reflector and is connected to the coils 43, 44.

[0147] The actuating means in particular comprise a pulling magnet.The yoke may comprise or consist of four soft iron cores and a cylindrical base plate surrounded by a coil.

[0148] The coils 43, 44 and the electronic components of the actuating device are arranged in a housing 47. The housing 47 can in particular be vacuum-tight. It can in particular form a boundary between a vacuum area and an area with a normal atmosphere.

[0149] The mirrors are arranged on the pupil facet carrier 13. The pupil facet carrier 13 can be connected to the housing 47 particularly firmly.

[0150] The two pairs of coils 43 , 44 are arranged relative to each other, in particular such that the connecting lines of their central axes intersect, in particular are orthogonal to each other.

[0151] A magnetic flux which is proportional to the controlled current in each case can be generated by means of the coil pairs 43, 44 via their pole shoes 40, 41. The magnetic flux generates a Lorentz force in combination with the permanent magnet 42 attached to the actuating pin 36. This force is used to apply a torque to the individual mirrors and thus to the flexure 33 via the actuating pin 36. The resulting tilt of the individual mirrors is proportional to the torque and thus to the coil current. This tilt is inversely proportional to the tilt stiffness of the flexure 33.

[0152] exist Figures 5 to 7 In the exemplary embodiment shown by way of example in FIG. 1 , no sensors are provided. The pupil facet 11 , in particular the pupil facet mirror 10 , is designed to be sensorless. This represents a considerable simplification compared to an arrangement in which a sensor for capturing the deflection of the magnet 42 must be inserted between the actuator and the magnet 42 .

[0153] As an alternative to a sensorless configuration, a configuration can also be provided in which measurement of the tilt of an individual mirror relative to only one of the two pivot axes 31, 32 is envisaged. Preferably, the pivoting movement of an individual mirror with a larger pivotable area about a pivot axis is detected by a sensor.

[0154] In principle, an embodiment is also possible with a sensor for one of the pivot axes 31 , 32 .

[0155] In a sensorless embodiment, the mirror orientation can preferably be set via the coil currents, which interact directly with the magnetic flux and thus with the generated forces and thus with the deflection of the permanent magnets 42, ie with the tilt of the individual mirrors.

[0156] The housing 47 can in particular be made of an electrically conductive metal, for example copper or a copper compound. This means that the tilting modes of the individual mirrors are subject to eddy current damping via the permanent magnets 42. This can suppress unwanted vibrations caused by mechanical vibrations.

[0157] For pupil facets 11 , in particular integral pupil facet mirrors 10 , a sensorless embodiment is particularly advantageous, also taking into account that otherwise required electrical feedthroughs and a purely metal housing 47 can be omitted.

[0158] The results show that, at least when the thermal load on the individual mirrors is sufficiently well defined, systematic and reproducible thermal variations in the controlled tilt angle of the individual mirrors can be counter-compensated with the aid of the compensation model, with typical correction voltage factors ranging between 3 and 10.

[0159] Long-term drifts of the zero position can be accounted for by an external calibration system which detects the angular deviations of the light rays reflected by the pupil facets 11 and determines therefrom the correction of the actuation signal.

[0160] Alternatively, the tilt angle may also be referenced relative to the end stops 38, 39. Figure 5 As shown, the outer end stop ring 39 can be designed so that in the two actuation directions unique pivotability boundaries occur, ie pivotability boundaries that are independent of the respective other actuation directions.

[0161] In order to controllably detect the end stop position, a current ramp can be applied to the coil pair 43 or 44 responsible for the corresponding pivot direction. As a result, the permanent magnet 42 with the associated end stop ring can be deflected at a constant speed in a quasi-static manner, especially below the resonance frequency. In the event of a collision between the contact surface of the fixed end stop ring 39 and the contact surface of the mobile end stop ring 38, the speed of the permanent magnet 42 changes suddenly. In the event of an elastic collision, the direction of the speed of the permanent magnet 42 is reversed. This can be determined as a jump in the back electromotive force. This jump can be associated with the current value at this station and therefore represents a calibration support point. Therefore, from the two end stop positions of each of the two pivot axes 31, 32, two calibration support points for the corresponding current angle characteristics of the corresponding pivot axes 31 and 32 can be obtained. This is sufficient for offset and / or gain correction. This is sufficient for small pivot angles, as shown in the figure, especially because the main errors are gain (especially due to temperature increase of the magnet 42 and the flexure 33) and offset (especially due to flexure creep).

[0162] Alternatively, a reference position sensor can be provided. By means of the reference position sensor, a reference signal, preferably in the central area of ​​the pivoting area, can be provided for each of the two pivot axes 31, 32 for correcting position offset drift. This concept is based on the discovery that the gain, i.e. the relationship between the change in current and the change in the inclination angle, varies significantly systematically, reversibly and reproducibly. Therefore, if necessary, small errors can be corrected to a sufficient extent relatively easily using a model. Position offsets usually undergo irreversible changes. However, calibration points of the pivot axis 31 or 32 are sufficient to correct the position offset.

[0163] According to another alternative, pupil facets 11 may be equipped with a simple sensor concept. For example, at least a subset of pupil facets 11, in particular all pupil facets 11, may be equipped with eddy current sensors for one or both of the pivot axes 31, 32.

[0164] Figure 8 By way of example the necessary tilting of the pupil facets 11 required to control three adjacent field facets 7 is shown. The middle point 50 corresponds to the neutral position of the actuator.

[0165] The upper point cloud 51 and the lower point cloud 52 correspond to the respective tilts required to reach two adjacent field facets 7. They show that the tilted surface normal is in a neutral position relative to the surface normal. It is qualitatively clear that the required pivoting movement about the x-axis (i.e. about the axis perpendicular to the scanning direction) is much larger, in particular, about an order of magnitude higher than the required pivoting movement about the vertical axis (y-axis).

[0166] In order to produce a nanostructured or microstructured device, such as a semiconductor memory chip, firstly a reticle 19 and a wafer 24 having a coating which is photosensitive to the illumination light 3 are provided.

[0167] Depending on the structural configuration on the reticle 19 or depending on the required resolution, the corresponding illumination setting is selected by a corresponding selection of the pupil facets 11 to be illuminated. This is achieved by the tiltable field facets 7 and the switching of the pupil facets 11. S The schematic diagram shown in Figure 1 The central control device 37a controls this tilting.

[0168] Different boundary conditions can be used to specify switching pupil facets 11 S The total number N of pupil facets 11 in the pupil facet mirror 10 ges The percentage A in the pupil surface. A desired pupil filling degree p of the illumination optical unit 25 can be specified. The pupil filling degree p is defined as the ratio of the pupil surface to which the illumination light is applied in the illumination optical unit 25 relative to the entire pupil surface.

[0169] For more details, please refer to DE 10 2018 214 223 A1.

[0170] After the illumination settings have been selected, a portion of the reticle 19 is first projected onto the wafer 24 by means of the projection exposure apparatus 1. The photosensitive layer on the wafer 24 that has been exposed by the illumination light 3 is then developed.

Claims

1. An individual mirror (11) of a pupil facet mirror (10) of an illumination optical unit (25) of a projection exposure apparatus (1), 1.1 having a reflective surface (34), wherein the reflective surface has a surface normal; 1.2 having bearings which enable the individual reflector (11) to perform a pivoting movement about two pivot axes (31, 32) extending transversely to the surface normal; as well as 1.3 having actuator means for pivoting the individual reflectors (11); 1.4 The ratio of the pivotability of the individual reflectors (11) around the two pivot axes (31, 32) is at least 2:

1.

2. The individual reflector (11) according to claim 1, characterized in that The smaller of the two pivotable areas is at most + / - 25 mrad.

3. An individual reflector (11) according to claim 1 or 2, characterized in that The bearing has one or more leaf springs for each pivoting degree of freedom, wherein the leaf spring for one pivoting degree of freedom is thicker and / or stiffer than the leaf spring for another pivoting degree of freedom.

4. An individual reflector (11) as claimed in any one of the preceding claims, characterized in that At most one pivoting movement about the two pivot axes (31, 32) is detected by the sensor device.

5. An individual reflector (11) according to any one of the preceding claims, characterized in that A sensor arrangement with one or more eddy current sensors is used to detect the pivot axis position.

6. An individual reflector (11) according to any one of the preceding claims, characterized in that The pivot shaft (31, 32) is arranged to be spaced apart from the reflective surface (34).

7. An individual reflector (11) according to any one of the preceding claims, characterized in that A reference position sensor is provided for determining one or more reference signals of the pivot position of one or both of the two pivot axes (31, 32).

8. An individual reflector (11) according to any one of the preceding claims, characterized in that The ratio of the pivotability about the two pivot axes (31, 32) is different from the ratio of the extent of the reflective surface of the individual reflector (11) in the various directions.

9. An individual reflector (11) as claimed in any one of the preceding claims, characterized in that The reflecting surfaces of the individual reflectors have the same size in a direction perpendicular to the two pivot axes (31, 32).

10. A pupil facet mirror (10) for an illumination optics unit (25) of a projection exposure apparatus (1), comprising a plurality of individual mirrors (11) as claimed in any one of the preceding claims.

11. An illumination optical unit (25) for a projection exposure apparatus (1), comprising: 11.1 A field facet reflector (6) having a plurality of field facets (7); as well as 11.2 The pupil facet mirror (10) as claimed in claim 10, by means of which the field facets (7) can be imaged into the object field (20).

12. The illumination optical unit (25) according to claim 11, characterized in that At least a subset of the pupil facets (11) are displaceable, enabling the pupil facets to be assigned exactly to two, three, four or five different field facets (7).

13. The illumination optical unit (25) according to claim 11 or 12, characterized in that The individual mirrors (11) of the pupil facet mirror (10) are aligned so that they have less pivotability in the cross-scan direction than in the scan direction.

14. A microlithography projection exposure apparatus (1), comprising: 14.1 The illumination optical unit (25) according to any one of claims 11 to 13; 14.2 A radiation source (2) for generating illuminating radiation (3); and 14.3 A projection optical unit (21) for imaging the mask master plate (19) arranged in the object field (20) into the image field (22).

15. A method for manufacturing a microstructure or nanostructure device, The following steps are involved:

15. 1 Providing a projection exposure apparatus (1) as claimed in claim 14; 15.2 Arranging a mask master (19) having a structure to be imaged in the object field (20) of the illumination optical unit (25); and 15.3 Imaging the structure on the reticle (19) onto a radiation-sensitive coating of a wafer (24) arranged in the image field (22) by means of the projection optical unit (21).

16. A method for calibrating the pivoting movement of an individual reflector (11) as claimed in any one of claims 1 to 9, comprising the following steps: 16.1 pivoting the individual reflector (11) at a constant pivoting speed; 16.2 Determine the back EMF distribution; 16.3 determining the jump location in the back EMF distribution; and 16.4 The calibration support point is determined by the current value at the jump position.

17. The method according to claim 16, characterized in that For each pivoting degree of freedom two calibration support points are determined which are used to determine the offset and / or gain correction.

18. The method according to claim 16 or 17, characterized in that A reference position sensor is used to determine a reference signal.

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