Support structure for an illumination optical unit of a projection exposure apparatus

Abstract

A support structure (46) open on one side for an illumination optical unit (15) of a microlithographic projection exposure apparatus (1) has a frame (46) extending in a longitudinal direction (37), with one or more means for increasing the stiffness of the frame (46), wherein ribs (48) and / or planar stiffening elements (47, 42, 43) serve as stiffening means.

Description

[0001] Support structure for an illumination optical unit of a projection exposure apparatus

[0002] The content of the German Patent Application DE 10 2023 208 965.3 is incorporated by reference herein.

[0003] The invention relates to a support structure for an illumination optical unit of a projection exposure apparatus. The invention additionally relates to an illumination optical unit, an illumination system, an optical system and a projection exposure apparatus comprising a corresponding support structure. Finally, the invention relates to a method for producing a microstructured or nano structured component and also to a component produced according to the method.

[0004] In illumination systems with a small chief ray angle at object (CRAO), the last optical element in the light path upstream of the reticle is arranged near the separating plane between the illumination system and the projection optical unit. A support structure is usually provided for arranging the optical components. On account of the small distance relative to the separating plane, the installation space available for the support structure is limited at least in one direction.

[0005] One object of the invention consists in improving a support structure for an illumination optical unit of a projection exposure apparatus.

[0006] This object is achieved in particular by a support structure having the claimed features. In accordance with one aspect of the invention, the support structure has one or more means for increasing the stiffness of a frame. In particular, a selection from ribs, struts and planar stiffening elements can serve as stiffening means. In particular, partition walls, in particular bulkheads, can also serve as stiffening elements. It has been found that, in particular, a frame open on one side can be stiffened in a targeted maimer by use of surface stiffnesses and / or arrangement of ribs and / or struts. This makes it possible to ensure that the support structure satisfies the ever increasing requirements, in particular with regard to their mechanical and dynamic properties. The support structure, in particular the frame, can be configured in particular in such a way that at least the first natural frequency is greater than 100 Hz, in particular greater than 200 Hz, in particular at least greater than 400 Hz.

[0007] It is assumed hereinafter that the projection optical unit and the illumination optical unit of a projection exposure apparatus are substantially arranged in disjoint half-spaces separated from one another by a separating plane. In this case, the separating plane can be oriented in particular perpendicular to the object plane in which the reticle is arranged. The separating plane can be oriented in particular parallel to the cross-scan direction.

[0008] Longitudinal direction is understood hereinafter to be a direction parallel to the chief ray incident on the reticle or a direction perpendicular to the object field. The longitudinal direction deviates from a normal to the object plane generally by at most 30°, in particular 20°, in particular at most 10°.

[0009] The support structure serves in particular for arranging optical components. It serves in particular for spatially fixing optical components in particular within the illumination optical unit. The support structure can be adjustable in particular relative to a reference system of the projection exposure apparatus.

[0010] Within the illumination optical unit, the support structure itself can form a reference system.

[0011] In accordance with one aspect, the frame is open at least sectionally. In particular, the frame can be open at least sectionally on one side. It can be open in particular on a side facing the separating plane, in particular in a transverse direction, i.e. transversely, in particular perpendicularly, with respect to the longitudinal direction.

[0012] The frame can have an overall extent in the longitudinal direction which is at least equal to the magnitude, in particular at least one and a half times the magnitude, in particular at least double the magnitude, of its maximum extent in the transverse direction. This has proved to be useful for the arrangement of various components of the illumination optical unit on the frame.

[0013] The ribs and / or the stiffening elements can be configured in a profiled fashion. They can have a T-profile, an H-profile, a C-profile, a V-profile or an X-profile in cross-section, in particular. As a result, the stiffness can be increased further in specific directions.

[0014] In accordance with one aspect, the frame is open over at least 50%, in particular at least 60%, in particular at least 70%, in particular at least 80%, in particular at least 90%, of its extent in the longitudinal direction, in particular completely, towards a side in a transverse direction with respect to the longitudinal direction. It can be open in particular in a direction perpendicular to the longitudinal direction.

[0015] The open side can face in particular the separating plane between the illumination optical unit and the projection optical unit.

[0016] In a further aspect, the support structure has an outwardly plane boundary wall on the side towards which the frame is open. This makes it possible to arrange the support structure as near as possible to the separating plane between the illumination optical unit and the projection optical unit. The separating plane can lie in particular in the region of the free area of the boundary wall.

[0017] In accordance with a further aspect, the frame can have a triangular crosssection or a trapezium-shaped cross-section or a pentagonal cross-section at least sectionally in a transverse, in particular perpendicular, direction with respect to the longitudinal direction. Generally, the cross-section of the frame in a transverse, in particular perpendicular, direction with respect to the longitudinal direction can be configured in a polygonal fashion at least sectionally.

[0018] The support structure can be configured in particular in such a way that the frame has a triangular cross-section at a first position in the longitudinal direction and a trapezium-shaped cross-section at a second position in the longitudinal direction.

[0019] Particularly high stiffnesses can be achieved by way of a triangular and / or a trapezium-shaped and / or a pentagonal cross-section. In this case, a trapezium is understood to be in particular a non-rectangular and non-parallelogram-shaped trapezium. The trapezium has in particular parallel base sides having different lengths. As a result, shear tolerances can be reduced, in particular avoided.

[0020] In accordance with a further aspect, the frame can be bounded by three or more triangular or trapezium-shaped stiffening plates in the longitudinal direction. The frame can be bounded by three triangular stiffening plates in the longitudinal direction, in particular.

[0021] The frame can have a smallest convex envelope which is bounded exclusively by triangular and quadrilateral, in particular trapezium-shaped, surfaces.

[0022] The frame can have in particular a pyramidal smallest convex envelope. In this case, the base surface of the envelope can be configured in a trapezium-shaped, non-rectangular or rectangular fashion. The base surface faces the separating plane, in particular. It can be oriented parallel to the separating plane, in particular.

[0023] The vertex of the pyramid can be situated perpendicularly above a boundary edge of the base surface.

[0024] The planar stiffening elements, in particular the stiffening plates, can be mounted in particular tangentially on a frame.

[0025] The frame can be configured with at least sectionally a C-shaped cross-section. In accordance with a further aspect, the frame can have receptacles for receiving optical components at opposite ends in the longitudinal direction. The optical components can be in particular facet mirrors of the illumination optical unit.

[0026] Generally, the frame can have connection points for attachments. The attachments can be in particular optical, mechanical or electrical components, in particular modules, of the projection exposure apparatus, in particular of the illumination optical unit. The attachments can have their own attachment housing, in particular.

[0027] Receiving optical components and / or attachments, in particular modules, in corresponding receptacles of the frame enables the stiffness of the frame to be further improved. It is possible, in particular, to use the stiffness of the optical components and / or of the attachments, in particular the housings thereof, for stiffening the support structure.

[0028] The corresponding optical components and / or attachments can be fixedly or releasably connected to the frame. They can be screwed, clamped or welded to the frame, in particular. All kinds of interlocking or force-locking connection techniques are preferred. However, integral bonding is not ruled out here.

[0029] In accordance with a further aspect, one or more stiffening elements can be arranged in the interior of the frame. These can be oriented parallel to the longitudinal direction, perpendicular to the longitudinal direction or obliquely with respect to the longitudinal direction. In particular, struts or plates can serve as stiffening elements. The plates can have cutouts. The cutouts can be configured in particular in a maimer shaped as conic sections, in particular in parabolic or elliptic fashion, in particular in circular fashion.

[0030] Stiffening elements oriented transversely with respect to the longitudinal direction are also referred to as transverse stiffenings or transverse stiffening elements.

[0031] Stiffening elements oriented substantially parallel to the longitudinal direction can serve as separating plates between rectilinear sections in a folded beam path, in particular a narrowly folded beam path, of the illumination optical unit.

[0032] One, two, three or more intermediate bases can be arranged within the support structure, in particular in the frame. These can serve as transverse stiffenings.

[0033] The support structure can be configured in particular in such a way that it defines an interior configured in such a way that it enables an obstruction- free radiation path with individual rectilinear subsections having a length of in each case at least 1 m, in particular at least 1.5 m, in particular at least 2 m.

[0034] The subsections can be configured in particular in such a way that they form radiation-conical regions or radiation-frustoconical regions between on one side an intermediate focus and on the other side a first optical element, in particular a (the) first facet mirror, and / or between the first optical element, in particular a (the) first facet mirror, and a second optical element, in particular a (the) second facet mirror, and / or between the second optical element, in particular a (the) second facet mirror, a third optical element and / or a fourth optical element and / or the object field.

[0035] The chief ray angle and / or the folding angles in the beam path of the illumination optical unit can be in particular at most 10°, in particular at most 7°, in particular at most 6°.

[0036] It has been found that the support structure according to the invention results in a reduction of costs and a mass saving. Moreover, the requirements in respect of manufacturing accuracy were able to be reduced. The use of welding assemblies has resulted in greater freedom of design. The proposed type of construction with ribs and / or intermediate bases facilitates the separation of the support structure along said intermediate bases. These additionally provide the surfaces necessary for a connection of the modules (screw flanges or weld joints). Such modularization is cost-effective since the raw blocks are smaller and can be produced more economically and generally the degree of machining (and thus manufacturing outlay and time) is lower than in the case of a large monolithic structure.

[0037] The mass saving is already afforded, inter alia, owing to the triangular or trapezium-shaped or polygonal basic shape, which allows less voluminous (and hence lighter) support structures than the customary type of construction in a rectangular shape.

[0038] Further objects of the invention consist in improving an illumination optical unit, an illumination system, an optical system for a projection exposure apparatus, and also a projection exposure apparatus. These objects are achieved by the corresponding optical units / systems comprising a support structure in accordance with the description above.

[0039] In accordance with one aspect, at least one optical component can be supported by the support structure. It is possible, in particular, to position one or two facet mirrors in the beam path of the illumination optical unit with the aid of the support structure. The optical components, in particular the mirrors, can be positioned particularly precisely on account of the mechanical properties of the support structure. Where an arrangement of mirrors, in particular facet mirrors, on the support structure is described hereinafter, this should be understood as non-limiting. The corresponding statements can also relate to other optical components.

[0040] It is possible, in particular, for optical components, in particular one or two facet mirrors, to be arranged on the frame of the support structure, in particular to be connected to the frame. The two facet mirrors can be arranged thereon opposite one another, in particular. The two facet mirrors can be connected to the frame in each case at the end side on the frame, in particular.

[0041] The support structure is arranged in the illumination optical unit in particular in such a way that it is open in direction to the separating plane towards the projection optical unit.

[0042] The support structure can lie in particular completely in a half-space which faces away from the projection optical unit and which is defined by a plane perpendicular to the object plane, in particular parallel to the cross-scan direction. In accordance with one aspect, a chief ray angle at object can be at most 10°, in particular at most 7°, in particular at most 6°.

[0043] In accordance with a further aspect, a distance between the last optical element in the beam path of the illumination radiation upstream of the reticle, in particular the last mirror, in particular the second facet mirror, and a plane bounding the support structure towards the open side can be at most 10 cm, in particular at most 5 cm, in particular at most 3 cm, in particular at most 2 cm, in particular at most 1 cm.

[0044] In accordance with a further aspect, an object-side numerical aperture can be at least 0.3, in particular at least 0.5.

[0045] An illumination system has, besides an illumination optical unit in accordance with the description above, a radiation source for generating illumination radiation, in particular an EUV radiation source. In particular, illumination radiation in the EUV range, in particular having a wavelength of less than 30 nm, in particular less than 15 nm, can be generated by means of an EUV radiation source.

[0046] An optical system comprises an illumination optical unit in accordance with the description above and a projection optical unit for transferring illumination radiation from the object field into an image field.

[0047] A projection exposure apparatus has, besides an illumination system in accordance with the description above, a projection optical unit for transferring illumination radiation from the object field into an image field. A method for producing a microstructured or nanostructured component is improved by providing a projection exposure apparatus in accordance with the description above. The improved mechanical properties of the support structure enable the microstructured or nanostructured components to be produced more precisely.

[0048] In accordance with the method, a reticle, with structures to be imaged, is arranged in the object field of the illumination optical unit. The structures of the reticle are imaged with the aid of illumination radiation, in particular in the EUV range, onto a radiation-sensitive layer of a wafer arranged in the image field of the projection optical unit. Further details of the method are known from the prior art, for example WO 2019 / 174 996 Al, to which reference is hereby made.

[0049] Further advantages and details of the invention will become apparent from the description of exemplary embodiments with reference to the figures, in which:

[0050] Figure 1 schematically shows the constituent parts and the beam path in a projection exposure apparatus,

[0051] Figure 2 schematically shows an arrangement of an optical component near to a separating plane between the illumination optical unit and the projection optical unit,

[0052] Figure 3 schematically shows an exemplary illustration of a support structure for an illumination optical unit, Figure 4 schematically shows a view of the support structure in accordance with Figure 3 from above,

[0053] Figure 5 schematically shows an illustration of a support structure of an illumination optical unit with a highlighted frame, and

[0054] Figure 6 schematically shows a view of the frame in accordance with Figure 5 for elucidating further details.

[0055] A microlithographic projection exposure apparatus 1 serves for producing a microstructured or nanostructured electronic semiconductor component. A light or radiation source 2 emits EUV radiation 3 in the wavelength range of, for example, between 0.2 nm and 30 nm, in particular between 0.1 nm and 15 nm.

[0056] Figure 1 shows main components of one of the projection exposure apparatuses 1 highly schematically.

[0057] The radiation source 2 is part of a radiation source module. Proceeding from the radiation source module, the illumination and imaging light 3 passes through an intermediate focus 4 and from there is guided by means of an illumination optical unit 15 towards an object field 11 of the projection exposure apparatus 1, in which object field a lithography mask 12 in the form of a reticle as object to be projected is arranged.

[0058] The illumination optical unit 15 includes a field facet mirror 16 and a second facet mirror, which is referred to hereinafter as pupil facet mirror 17 even if this mirror need not be arranged in a pupil plane, the function of which mirrors corresponds to that known from the prior art, and which are therefore merely illustrated extremely schematically and without the associated EUV beam path in Figure 1.

[0059] After reflection at the field facet mirror 16, the EUV pencil of rays is incident on the pupil facet mirror 17. The individually actuatable subelements of the first optical element are assigned to those of the second optical element depending on a desired illumination by the projection exposure apparatus 1. The illumination light 3 is therefore guided for predefining individual illumination angles along the illumination channel sequentially via pairs comprising in each case one or more individual subelements of the first and second optical elements. These subelements are each tilted individually for control purposes.

[0060] Via the pupil facet mirror 17 and, if appropriate, via a downstream transfer optical unit (not illustrated), the individual light portions are imaged into the illumination or object field 11 in a reticle or object plane 18 of a projection optical unit 19 (likewise illustrated schematically in Figure 1) of the projection exposure apparatus 1.

[0061] In a further embodiment of the illumination optical unit 15, in particular given a suitable position of an entrance pupil of the projection optical unit 19, it is also possible to dispense with the mirrors of the transfer optical unit upstream of the object field 11, which leads to a corresponding increase in the transmission of the projection exposure apparatus 1 for the used radiation beam.

[0062] The reticle 12, which reflects the used radiation beam, is arranged in the object plane 18 in the region of the object field 11. The reticle 12 is carried by a reticle holder 20, which is displaceable in a manner controlled by means of a reticle displacement drive 21.

[0063] The projection optical unit 19 images the object field 11 into an image field 22 in an image plane 23. During the projection exposure, a wafer 24 is arranged in said image plane 23, said wafer bearing a light-sensitive layer which is exposed during the projection exposure by the projection exposure apparatus 1. The wafer 24 is carried by a wafer holder 25, which is in turn displaceable in a maimer controlled by means of a wafer displacement drive 26.

[0064] During the projection exposure, both the reticle 12 and the wafer are scanned in a synchronized manner in the scan direction by corresponding control of the reticle displacement drive 21 and of the wafer displacement drive 26. The wafer can be scanned at a scan rate of typically 600 mm / s in the x-direction during the projection exposure.

[0065] Figure 2 illustrates schematically and by way of example the installation space conditions between the last optical element 31 in the beam path of the illumination optical unit 15 and the reticle 12.

[0066] The illumination radiation 3 has a chief ray direction 32. The chief ray direction can be characterized by the chief ray angle 33. The emission angle 33 is also referred to as the chief ray angle at object for incidence on the reticle 12.

[0067] Figure 2 schematically illustrates a separating plane 34 between the illumination optical unit 15 and the projection optical unit 19. The separating plane 34 can be oriented in particular perpendicular to the object plane 18. The separating plane 34 defines the virtual separation between the halfspace in which the illumination optical unit 15 is arranged and the halfspace in which the projection optical unit 19 is arranged.

[0068] Given a small beam angle 33, the distance A between the last optical element 31 of the illumination optical unit 15 and the separating plane 34 is very small. In particular, besides being dependent on the chief ray angle 33, the distance A is also dependent on the size, in particular the extent, of the last optical element 31 in a direction perpendicular to the separating plane 34.

[0069] The distance A is required for optical production methods and / or a module mechanism (not illustrated) enclosing the optical element 31.

[0070] Merely for elucidation purposes, Figure 2 also illustrates a beam 35 incident on the last optical element 31. Particularly if the beam path in the illumination optical unit 15 is narrowly folded, the reduced installation space availability associated therewith results in difficult requirements in respect of a support structure 36 used for supporting, i.e. positioning, the optical components of the illumination optical unit.

[0071] Such a support structure 36 is illustrated by way of example in Figures 3 and 4.

[0072] The support structure 36 is open on one side. It has in particular an opening 38 extending in a longitudinal direction 37. In this case, the longitudinal direction 37 can coincide with a normal object plane 18 or can be parallel to such a normal direction.

[0073] The support structure 36 has a first receptacle 39 for receiving a first optical element. The first receptacle is the upper receptacle in Figure 3. This should be understood as non-limiting. The support structure 36 can also be arranged in a differently oriented maimer in the projection exposure apparatus 1.

[0074] The first optical element that can be arranged in the first receptacle 39 can be in particular a first facet mirror, in particular the field facet mirror 16. The first optical element is received in the first receptacle 39 in a manner connected to the support structure 36 in particular fixedly or by way of a compensating element. The compensating element can serve for example for compensation of thermal expansion or dynamic decoupling or setting (adjustment) of the optical elements. The optical element or the compensating element can be screwed, clamped or welded to the support structure 36, in particular.

[0075] At the opposite end in the longitudinal direction 37, the support structure has a second receptacle. The second receptacle 40 serves for receiving a second optical element. The second optical element can be a second mirror, in particular a second facet mirror, in particular the pupil facet mirror 17.

[0076] An open region 41 is discernible in Figure 4. Through the open region 41 the illumination radiation 3 passes from the last optical element 31 of the illumination optical unit 15 to the object field 11. A plurality of transverse stiffenings 42 are arranged in the support structure 36. In particular, stiffening plates can serve as transverse stiffenings 42. The stiffening plates can each have cutouts 45 enabling the obstructed passage of illumination radiation 3.

[0077] The cutouts 45 can each be configured in elliptic fashion, in particular in circular fashion.

[0078] A longitudinal stiffening 43 is arranged in the support structure 36. A stiffening plate serves as longitudinal stiffening 43. A cutout for allowing EUV radiation 3 to pass through can be provided for the longitudinal stiffening. As is illustrated schematically and by way of example in Figure 3, the cutout 44 in the longitudinal stiffening 43 can be configured in parabolic fashion.

[0079] The support structure 36 encloses the beam path of the illumination optical unit 15 substantially in the shape of the letter C. The support structure 36 thus constitutes a structure open on one side.

[0080] The support structure 36 has a plane boundary wall 49 towards the open side. The free surface of the boundary wall 49 can coincide with the separating plane 34. It is generally preferably oriented parallel to the separating plane 34.

[0081] By means of lateral projections 50, the support structure 36 can be arranged, in particular secured, on bearing supports in the projection exposure apparatus 1. In order to increase the stiffness, in particular the torsional stiffness, of the support structure 36, the latter can have a frame 46. The frame 46 is highlighted by way of example in Figure 5. It is illustrated purely schematically in Figures 5 and 6.

[0082] The frame 46 can be further stiffened with the aid of the ribs 48. In this case, the ribs 48 can form shaping ribs of the frame 46. An outer skin, in particular in the form of the stiffening plates 47, can then be applied to the ribs.

[0083] The frame 40 with ribs 48 and / or stiffening plates 47 allows, in particular on account of the regular structure, the manufacture of small subsections which can be connected to form the complete support structure 36. The costs and the necessary manufacturing accuracies can be reduced as a result.

[0084] On account of the triangular and / or trapezium- shaped cross-section, in particular in combination with the rib type of construction, it is possible to achieve a saving of mass and volume and hence a reduction of the degree of machining in comparison with support structures having rectangular cross-sections.

[0085] The support structure 36 can be configured as a welding assembly. This affords greater freedom of design on account of an advantageous segmentation.

[0086] In addition, smaller raw material sections are more easily procurable and more easily producible and manageable with regard to their material quality and material homogeneity.

Claims

Patent Claims1. Support structure (36) for an illumination optical unit (15) of a micro- lithographic projection exposure apparatus (1) having1.

1. a frame (46) extending in a longitudinal direction (37),1.1.

1. which frame only partly circumferentially surrounds a radiation cross-sectional region in a plane perpendicular to the longitudinal direction (37), and1.

2. one or more means for increasing the stiffness of the frame (46) selected from the following list: ribs (48), struts, planar stiffening elements (47, 42, 43).

2. Support structure (36) according to Claim 1, characterized in that the frame (46), over at least 50% of its extent in the longitudinal direction (37), is open towards one side in a transverse direction with respect to the longitudinal direction (37).

3. Support structure (36) according to Claim 2, characterized in that it has an outwardly plane boundary wall (49) on the side towards which the frame (46) is open.

4. Support structure (36) according to any of the preceding claims, characterized in that the frame (46) has a triangular or trapezium-shaped or pentagonal cross-section at least sectionally in a transverse direction with respect to the longitudinal direction (37).

5. Support structure (36) according to any of the preceding claims, characterized in that the frame (46) is bounded by at least one triangular or trapezium-shaped stiffening plate (47) in the longitudinal direction (37).

6. Support structure (36) according to any of the preceding claims, characterized in that the frame (46) is bounded towards the outside by three or four substantially triangular planar stiffening elements (47).

7. Support structure (36) according to any of the preceding claims, characterized in that the frame (46) has receptacles (39, 40) for receiving optical components at opposite ends in the longitudinal direction (37).

8. Support structure (36) according to any of the preceding claims, characterized in that one or more stiffening elements (42, 43) are arranged in the interior of the frame (46).

9. Illumination optical unit (15) for a microlithographic projection exposure apparatus (1) having9.

1. a support structure (36) according to any of the preceding claims, and9.

2. at least one optical component which is supported by the support structure (36).

10. Illumination optical unit (15) according to Claim 9, characterized in that a chief ray angle at object (CRAO) is at most 10°.

11. Illumination optical unit (15) according to either of Claims 9 and 10, characterized in that a distance A between the last optical element (31) in the beam path upstream of the reticle (12) and a plane (34) bounding the support structure (36) towards the open side is at most 15 cm.

12. Illumination optical unit (15) according to any of Claims 9 to 11, characterized in that an object-side numerical aperture (NAO) is at least 0.3.

13. Illumination system for a microlithographic projection exposure apparatus (1) having13.

1. an illumination optical unit (15) according to any of Claims 9 to 12, and13.

2. a radiation source (2) for generating illumination radiation (3).

14. Optical system for a microlithographic projection exposure apparatus (1) having14.

1. an illumination optical unit (15) according to any of Claims 9 to 12, and14.

2. a projection optical unit (19) for transferring illumination radiation (3) from the object field (11) into an image field (22).

15. Microlithographic projection exposure apparatus (1) having15.

1. an illumination system according to Claim 13, and15.

2. a projection optical unit (19) for transferring illumination radiation (3) from the object field (11) into an image field (22).

16. Method for producing a microstructured or nanostructured component comprising the following steps:16.

1. providing a projection exposure apparatus (1) according to Claim 15,16.

2. arranging a reticle (12), with structures to be imaged, in the object field (11),16.

3. imaging the structures to be imaged onto an illumination-sensitive layer of a wafer (24) arranged in the image field (22).

17. Microstructured or nanostructured component produced according to a method according to Claim 16.

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