The present patent application claims the priority of the German patent application DE 10 2022 209 869.2, the content of which is incorporated herein by reference.

The invention relates to a holding device for an optical component having an optical surface with a polygonal border and having a cylindrical substrate body. The invention also relates to an optical assembly comprising such a holding device, to a method for determining the position of an optical component in such a holding device, to an illumination optical unit comprising such an optical assembly, to an optical system comprising such an illumination optical unit, to an illumination system comprising such an optical system, and to a projection exposure apparatus comprising such an illumination system.

A holding device for an optical component in the form of a rod of an illumination device is known from DE 10 2007 050 456 Al.

DE 102 55 735 Al discloses a device for mounting a reflector rod. DE 103 11 809 Al discloses a polarization-optimized illumination system. CN 209 132 491 U discloses a holding structure for an optical integrator.

It is an object of the present invention to provide a holding device which makes it possible to securely hold optical components having an optical surface with a polygonal border and having a cylindrical substrate body and enables positionally accurate mounting. This object is achieved according to the invention by a holding device having the features specified in Claim 1.

According to the invention, it was recognized that the mount can be subdivided into functional groups, specifically for the one part a bearing body for defining a bearing point for the lateral wall of the substrate body, and at least one pressing body which presses a substrate body of the optical component against the bearing body. This enables defined and in particular positionally accurate mounting of the optical component. The at least two bearing bodies and/or the at least one pressing body may be in contact with the cylinder lateral wall of the substrate body by way of a respective contact point. The optical component may be an optical rod, which can be used in particular for light mixing in a projection exposure apparatus for microlithography. The polygon for defining the optical surface with a polygonal border of the optical component is an n-gon with n comers, with n being greater than 4, for example a pentagon, a hexagon or an octagon, n is usually less than 100. A position of the holding frame of the holding device may be defined by a position of a holding mount of the holding device.

The holding device makes it possible to enable open-loop or closed-loop control of the definition of the position of the optical component. To that end, the holding device may have at least one displacement actuator for at least one of the bearing bodies and optionally also a position sensor.

An embodiment of the holding device according to Claim 2 having at least two pressing bodies has proven successful in practice. The at least two pressing bodies can press on the lateral wall of the substrate body by way of assigned bearing portions of the lateral wall of the substrate body in one and the same cross-sectional plane. The substrate body is held in defined fashion at an axial position between its two optical surfaces as a result. The holding device may have exactly three pressing bodies, which define a holding plane via their assigned bearing portions, by way of which they press on the lateral wall of the substrate body. This holding plane may be perpendicular to a cylindrical axis of the substrate body, that is to say parallel to the cross-sectional plane of the cylinder lateral wall.

This applies in particular to pressing bodies with bearing pressures corresponding to those of Claims 3 and 4.

An embodiment of the holding device according to Claim 5 enables openloop or optionally closed-loop control of the definition of the position for the optical component. In the event of manipulation, the bearing body can then be adjusted towards and/or away from the bearing portion. Such an adjustment may be performed by a motor. The bearing body may in that case have an adjustment actuator.

An embodiment with three bearing bodies according to Claim 6 enables a defined positional geometry.

This applies especially to a contact geometry according to Claim 7.

The advantages of an optical assembly according to Claim 8 correspond to those that have already been explained above with reference to the holding device.

In the case of an embodiment of the pressing body according to Claim 9, the bearing bodies can be used to positionally define the optical component relative to the holding device. A further object of the invention is to specify a method for determining the position of the optical component when the holding device is in use.

This object is achieved according to the invention by a position determining method comprising the steps specified in Claim 10.

Determination of an angle and at least two relative positions of bearing body contact points makes it possible to determine a relative position of the cross section of the cylinder lateral wall of the optical component in the holding device.

The advantages of an illumination optical unit according to Claim 11, an optical system according to Claim 12, an illumination system according to Claim 13 and a projection exposure apparatus according to Claim 14 correspond to those that have already been explained above with reference to the holding device, the optical assembly and the position determining method.

The illumination system can have a DUV (deep ultraviolet) light source.

In particular, a microstructured or nanostructured component, especially a semiconductor chip, for example a memory chip, can be produced using the projection exposure apparatus.

Exemplary embodiments of the invention are explained in greater detail below with reference to the drawing, in which: Figure 1 shows a schematic overview of a projection exposure apparatus for microlithography in a meridional section, having an optical rod for mixing illumination light;

Figure 2 shows a cross section through an embodiment of the optical rod in a holding device, which is not illustrated in Figure 1;

Figure 3 shows a further embodiment of the optical rod in a further embodiment of the holding device in an illustration similar to Figure 2;

Figure 4 schematically shows parameters which play a role in determining the position of the rod in the holding device and in Figure 3.

In order to elucidate positional relationships, a Cartesian xyz-coordinate system is specified in the drawing. In Figure 1, the x axis extends perpendicularly to and beyond the plane of the drawing. The y axis extends upwards in Figure 1. The z axis extends to the left in Figure 1.

A projection exposure apparatus 1 for microlithography has an illumination system comprising an illumination optical unit 2 for illuminating a defined illumination and object field 3 at the location of an object and a reticle 4, which represents a template to be projected for the production of microstructured or microelectronic semiconductor components. The reticle 4 is held by a reticle holder, which is not illustrated here. A laser in the deep ultraviolet (DUV) is used as a light source 5 for the illumination light of the illumination system. This could be an ArF excimer laser. Other DUV sources are also possible.

A beam expander 6, for example a mirror arrangement known from DE-A 41 24 311, is used to reduce coherence and generate an expanded, collimated, rectangular cross section of a beam of the illumination light 7.

A first diffractive optical raster element (DOE) 8 is disposed in an object plane of a condenser 9. This DOE 8 is also referred to hereinafter as intensity specification element. The condenser 9 comprises an axicon pair 10 and a lens element 11 with a positive focal length. The spacing between the axicon elements of the axicon pair 10 and the position of the lens element 11 are adjustable along an optical axis 12 of the illumination optical unit 2, as indicated by double-headed arrows 13, 14 in Figure 1. Therefore, the condenser 9 represents a zoom optical unit.

A further diffractive and/or refractive optical raster element (ROE) 16 is disposed in an exit pupil plane 15 of the condenser 9. Where the raster element 16 is diffractive, it may be in the form of a computer-generated hologram (CGH), for example. As an alternative or in addition to the embodiment as a diffractive optical element, the ROE 16 may be refractive, for example in the form of a refractive optical raster element, in particular a microlens array. Although a diffractive embodiment is possible, the raster element 16 is denoted ROE below.

Using the first DOE 8, a defined intensity distribution in the pupil plane 15 is set at the location of the ROE 16. This generates a specified so-called illumination setting, i.e., a defined distribution of illumination angles over the object field 3. Therefore, the first DOE 8 represents an illumination angle specification element for specifying an illumination angle distribution over the object field 3.

An input coupling optical unit 17 downstream of the ROE 16 transmits the illumination light to an end-side entry surface 18 of a transparent optical rod in the form of a glass rod 19. Variants for the optical rod 19 and variants of holding devices for the optical rod 19 are also described below.

The optical rod 19 has a cross section which differs from a square or rectangular cross section. This rod cross section is generally polygonal and may for example be hexagonal. Other cross section examples are also described below on the basis of Figures 2 and 3.

The rod 19 mixes and homogenizes the illumination light by multiple internal reflection at the lateral walls of the rod 19. An intermediate field plane in which a reticle masking system (REMA) 21, an adjustable field stop, is disposed is located directly on an end-side exit surface 20 of the rod 19 which is situated opposite the entry surface 18.

The ROE 16 is used, inter alia, to adapt the cross-sectional shape of the illumination beam 7 to the rectangular shape of the entry surface 18 of the rod 19.

The ROE 16 is also referred to hereinafter as optical rod illumination specification element. The ROE 16 serves to specify an illumination of the entry surface 18 of the rod 19 by way of the illumination light 7. The illumination of the entry surface 18 is specified in such a way that it specifies the distribution of the illumination intensity and, at the same time, the illumination angle distribution over the entry surface 18. The specified illumination intensity distribution over the entry surface 18 deviates from a homogeneous distribution, as is yet to be explained in more detail below.

The DOE 8, i.e., the intensity specification element, is used to specify an illumination intensity distribution on the ROE 16, i.e., on the optical rod illumination specification element.

A condenser 22 is downstream of the REMA 21. A stop interchange holder 24 with a plurality of stops or filters can be disposed in an exit pupil plane 23 of the condenser 22, of which two stops 25, 26 are illustrated in Figure 1. The stop interchange holder 24 carries the various stops in the maimer of a stop carousel. For the purpose of changing the stop, the carousel is driven around a drive shaft 27 of a drive motor 28, which is signal-connected to a central open-loop control device 28a of the projection exposure apparatus 1. The stops of the stop interchange holder 24 are subdivided into an even number of separate stop portions. The stop portions may be stops that completely block the illumination light, neutral density filters that attenuate the illumination light by a defined percentage, or polarization filters that linearly polarize the illumination light.

A further condenser with lens-element groups 29, 30 is downstream of the pupil plane 23 that is downstream of the rod 19. A 90° deflection mirror 31 for the illumination light is disposed between the two lens-element groups 29, 30. The condenser 22 and the further condenser with the two lens-element groups 29, 30 form a lens 31a, which images the intermediate field plane of the REMA 21 onto the reticle 4. The pupil plane 23 represents an internal pupil plane of this lens 31a. A projection lens 32 images the object field 3, which lies in an object plane 33, into an image field 34 in an image plane 35. The image field 34 is part of the surface of a wafer 36 that is to be exposed, the wafer being provided with a coating which is sensitive to the illumination light. The wafer 36 is held by a wafer holder, which is not shown here. During the projection exposure, the reticle 4 and the wafer 36 are scanned synchronously with one another. An intermittent displacement of the holder of the reticle 4 and of the wafer 36, a so-called stepper operation, is also possible.

With the exception of the deflection mirror 31, the various beam-guiding or beam-shaping components of the projection exposure apparatus 1 are indicated as refractive components. However, they could equally be catadioptric or reflective components.

Figure 2 shows a cross section through a variant of an optical rod 37 which can be used in the projection exposure apparatus 1 instead of the optical rod 19. The optical rod 37 is an optical component having an optical surface with a polygonal border, that is to say an entry surface 18 with a polygonal border and an exit surface 20 (cf. also Figure 1). The optical rod 37 has a cylindrical substrate body or main body 38 comprising a cylinder lateral wall 39 with a polygonal cross section which corresponds to the border of the optical surfaces 18, 20.

Overall, the optical surfaces 18, 20 of the rod 37 have an octagonal polygonal border, with corresponding comers 40 of this cross-sectional polygon being numbered consecutively, starting from the upper left comer in Figure 2 and going clockwise, and being indexed with 401 to 40s Seven of the eight comers 40i are convex comers of the substrate body 38. Only one of the eight comers, the comer 404, is a concave comer of the substrate body 38. A polygon internal angle of the substrate body 38 is thus greater than 180° in the region of the comer 404. All other polygon internal angles are smaller than 180°.

There are planar portions of the lateral wall 39 between the comers 40i that extend perpendicularly to the plane of the drawing in Figure 2 and parallel to one another between the entry surface 18 and the exit surface 20 of the rod 37.

The optical rod 37 is held by a holding device 41 and positioned in defined fashion in its spatial position. The holding device 41 has a holding frame 42 with two mount bodies 43, 44. The mount bodies 43, 44 are pressing bodies for pressing the holding frame 41 into contact with the lateral wall 39 of the substrate body 38 by way of portions 45, 46 to be pressed of the lateral wall 39. The portion 45 to be pressed is between the comers 40i and 402. The portion 46 to be pressed is between the comers 40s and 40e. The portions 45, 46 to be pressed are wall portions of the lateral wall 39 that extend parallel to one another.

The pressing bodies 43, 44 exert bearing pressures FDI, FD2 on the portions 45, 46 to be pressed. These bearing pressures FDI, FD2 are illustrated by arrows in Figure 2.

The bearing pressures FDI, FD2 act in opposite directions. The bearing pressures FDI, FD2 act perpendicularly to the portions 45 and 46 to be pressed.

The holding device 41 has a further pressing body 47, which is in the form of a pressure piece. The pressing body 47 bears against a portion 48 to be pressed of the lateral wall 39 between the comers 40? and 40s (contact point A47). This bearing contact is effected via a crowned pressing body end portion 49. The bearing of the pressing body end portion 49 against the portion 48 to be pressed of the lateral wall 39 may approximate punctiform contact or else, depending on the embodiment of the pressing body end portion 49, linear contact, with a line of this linear contact extending perpendicularly to the plane of the drawing of Figure 2, that is to say parallel to the comer lines of the comers 40i. The pressing body end portion 49 may be designed in the maimer of a convex, crowned cylinder portion.

A bearing pressure exerted by the pressing body 47 along its longitudinal axis on the portion 48 to be pressed is depicted in Figure 2 by an arrow FD3.

The bearing pressures FDI, FD2 and FD3 all act in the plane of the drawing of Figure 2, that is to say parallel to the xy plane. The bearing pressure FD3 extends at an acute angle in relation to the xz plane. The pressure FDI acts in the negative x direction. The pressure FD2 acts in the positive y direction.

The three pressing bodies 43, 44, 47 of the holding device 41 serve to exert a bearing pressure, which presses the substrate body 38 of the rod 37 against a bearing of the holding device 41, the bearing being formed by two bearing bodies 50, 51 of the holding device 41.

The bearing bodies 50, 51 are in the form of manipulators or positioning elements. Bearing body end portions 52, 53 of the bearing bodies 50, 51 exert a bearing contact pressure on the lateral wall 39 of the substrate body 38 by way of bearing portions 54, 55 of the lateral wall 39. The bearing body end portions 52, 53 may be designed like the pressing body end portion 49 of the pressing body 47. The bearing portion 54 is between the comers 402 and 40s of the lateral wall 39. The bearing portion 55 is between the comers 40s and 404 of the lateral wall 39.

The bearing bodies 50, 51 are in the form of manipulators. The bearing bodies 50, 51 may be in the form of adjusting screws. The bearing bodies 50, 51 may, as indicated by double-headed arrows 56, 57 in Figure 2, be adjusted with a defined position towards and away from the bearing portions 54, 55. The adjustment direction extends along respective longitudinal axes L50, L51 of the bearing bodies 50, 51. This adjustment is effected by adjustment actuators 58, 59, which are indicated schematically in Figure 2.

The adjustment direction 56 of the bearing body 50 extends at approximately 45° in relation to the xz and the yz plane. The adjustment direction 57 extends at approximately 60° in relation to the xz plane and 30° in relation to the yz plane. Other angles of the adjustment directions 56, 57 in relation to these planes, xz and yz, in the range between 10° and 80° are also possible.

Together with the optical rod 37, the holding device 41 forms an optical assembly of the projection exposure apparatus 1.

To determine the position of the optical component 37, that is to say of the rod, in the coordinates of the holding frame 42 the following procedure is carried out: An angle a between two polygon faces of the cylinder lateral wall 39 is determined, for example the angle between the bearing portions 54 and 55.

Relative positions between contact points A50, A51, via which the bearing bodies 50, 51 are in contact with the lateral wall 39, with respect to one another and to two frame points A, B of the holding frame 42 are determined.

It is then possible to determine the relative position of the polygonal cross section of the cylinder lateral wall 39 with respect to the holding device 41 from these data a, A50, A51, A and B. In addition, it is also possible to use knowledge of the position of a further point of the cylinder lateral wall 39, for example the position of a contact point A47 of the pressing body 47 with the portion 48 to be pressed of the lateral wall 39 or the position of a further point, for example in the region of the bearing portions 54 or 55 of the cylinder lateral wall 39, to determine the relative position of the polygonal cross section of the cylinder lateral wall 39 with respect to the holding device 41. Contact points by way of which the pressing bodies 43, 44 of the holding device 47 bear against the portions 45, 46 to be pressed of the cylinder lateral wall may also be such an additional relative position which, when known, makes it possible to determine the relative position of the polygonal cross section of the cylinder lateral wall 39 with respect to the holding device 41.

On the basis of Figure 3, another embodiment of a holding device 61 for mounting, with a defined position, another embodiment of an optical component that has an optical surface with a polygonal border and is in the form of an optical rod 62 will be described below. Components and functions corresponding to those which have already been explained above with reference to Figures 1 and 2 have the same reference numerals and will not be discussed in detail again.

The holding device 61 has a pressing body 63, which is a mount body of a mount of a holding frame 64 of the holding device 61.

The optical rod 62 is in turn designed with a substrate body 38 having a polygonal cross section, which in the case of the optical rod 62 has a convex pentagonal (comers 401 to 40s) configuration.

The pressing body 63 exerts a pressure FD on a portion 65 to be pressed of the lateral wall 39 of the rod 62. This causes the rod 62 to be pressed into a bearing formed by three bearing bodies 66, 67, 68, which specify a concave contact geometry. A convex cross-sectional region of the optical rod 62, formed by bearing portions 69, 70, 71, between the comers 40s, 404, the comers 404 and 40s and the comers 40s and 40i is pressed into this concave contact geometry of the bearing bodies 66 to 68. The bearing bodies 66 to 68 are in turn formed by bearing body end portions in the maimer of the bearing body end portions 52, 53 of the embodiment according to Figure 2 and can ensure punctiform contact or linear contact with the bearing portions 69 to 71 of the lateral wall 39.

On the basis of Figure 4, the way in which the position of the optical rod 62 is determined when the holding device 61 is in use will be described below.

First of all, in turn an angle a between two polygon faces of the cylinder lateral wall 39 is determined, in this case between the bearing portions 69 and 71. Then, a relative position of contact points Aee, Ae?, Aes, by way of which the bearing bodies 66 to 68 bear against the bearing portions 69 to 71 of the lateral wall 39, with respect to two frame points A and B of the pressing body 63 of the holding frame 61 is determined. The relative position of the cross section of the cylinder lateral wall 39 and thus the relative position of the rod 62 with respect to the holding device 61 is then determined from these parameters a, Aee to Aes, A and B.

To determine the position of the optical component 37, 62 in the respective holding device 41, 61, it is alternatively or additionally possible also to use at least one position sensor, in particular a distance sensor. Such a position sensor can determine the respective position, in particular of one of the bearing bodies 50, 51 (Figure 2) or 66 to 68 (Figure 3). The pressing body 47 of the embodiment according to Figure 2 can also have such a position sensor.

A corresponding position sensor can be used for closed-loop control of the positioning of the bearing bodies 50, 51. To that end, the actuators 58, 59 and the at least one position sensor are signal-connected to the open-loop control device 28a, which is then also in the form of a closed-loop control device, of the projection exposure apparatus 1.

The mount of the holding device 41 or 61 may have a cylindrical overall form, this not being illustrated in the drawing.

In the case of the microlithographic production of a microstructured or nanostructured component, the wafer 36 is initially coated, at least in certain portions, with a light-sensitive layer. Then, a structure on the reticle 4 is projected onto the wafer 36 using the projection exposure apparatus 1. After that, the exposed wafer 36 is processed to form a microstructured component.