Microlithographic projection objective

Abstract

The invention relates to a microlithographic projection objective having a plurality of lenses (20A-20J, 24, 25), wherein the lenses (20A-20J, 24, 25) define an imaging beam path (17) between an object plane (12) and an image plane (21) and wherein the lenses (20A-20J, 24, 25) are designed to image a photomask (13) arranged in the object plane (12) onto a lithography object (15) arranged in the image plane (21). The projection objective comprises a frame device (23), wherein retaining feet (26A-26H, 46A-46H, 47A-47H) are attached to the frame device (23) and wherein the lenses (20A-20J, 24, 25) are supported by the retaining feet (26A-26H, 46A-46H, 47A-47H), wherein a first retaining foot (46A-46H) supports a first lens (24), wherein a second retaining foot (47A-47H) supports a second lens (25) and wherein a third retaining foot (26A-26H) supports a third lens (20A-20J). The first retaining foot (46A-46H) is attached to the frame device (23) in the same angular position (30) as the second retaining foot (47A-47H). The third retaining foot (26A-26H) is arranged in an angular position in which neither a first retaining foot (46A-46H) of the first lens (24) nor a second retaining foot (47A-47H) of the second lens (25) is arranged.

Description

Microlithographic projection lens

[0001] The present patent application claims priority from the German patent application DE 10 2024 205 017 . 2 filed on 29 May 2024, to which reference is made and whose content is fully incorporated here (“incorporation by reference”).

[0002] The invention relates to a microlithographic projection object.

[0003] Microlithographic exposure systems are used for the production of integrated circuits with particularly small structures. A photomask illuminated with short-wave ultraviolet radiation (DUV radiation) is imaged onto a lithographic object to transfer the mask structure onto the lithographic object.

[0004] The imaging beam path between the photomask and the lithographic object passes through a number of lenses. For the image to be of sufficient quality, the lenses must have a precisely defined geometric shape and be held in exact position relative to one another. Thermal deformation can occur if heat is supplied to the lenses or to the holding devices that hold them, negatively impacting image quality. One cause of unwanted heat input to the lenses can be the absorption of DUV radiation in components adjacent to a lens, with the resulting heat being transferred to the lens.

[0005] The invention is based on the objective of presenting a projection lens with which the aforementioned disadvantages are reduced. This objective is achieved with the features of the Independent claim. Advantageous embodiments are specified in the dependent claims.

[0006] A microlithographic projection object according to the invention comprises a plurality of lenses, wherein the lenses define an imaging beam path between an object plane and an image plane, and wherein the lenses are designed to image a photomask arranged in the object plane onto a lithographic object arranged in the image plane. The projection object comprises a frame device, wherein support feet are attached to the frame device and wherein the lenses are supported by the support feet. A first support foot supports a first lens, a second support foot supports a second lens, and a third support foot supports a third lens. The first support foot is attached to the frame device at the same angular position as the second support foot. The third support foot is arranged at an angular position in which neither a support foot for the first lens nor a support foot for the second lens is located.

[0007] In a microlithographic projection lens, it is advantageous to attach the mounting feet of different lenses to the frame at different angular positions. If the mounting feet of all lenses were at the same angular position, mechanical loads would accumulate at specific, discrete angular positions of the frame. Similarly, thermal loads acting on the lens would concentrate at these angular positions, potentially leading to a mutual amplification of aberrations between different lenses. By distributing the mounting feet of different lenses differently around the circumference of the frame, this mutual amplification of undesirable effects can be avoided.

[0008] The projection object according to the invention retains this conventional design principle, which is manifested in the fact that the third lens is supported by a third mounting base, wherein the third mounting base is arranged in an angular position that has no equivalent in the first or the second lens. According to the invention, it is proposed to make an exception to the conventional design principle for the first and the second lens by having the first and the second lens mounting bases that are arranged in the same angular position.

[0009] The inventive rationale for this deviation from the conventional design principle is that the possibility of shading between the mounting feet of the first lens and the mounting feet of the second lens is to be utilized. Portions of the DUV radiation absorbed at a mounting foot of the first lens cannot contribute to heating the second lens. If the second lens has a mounting foot arranged at an angle that is shaded by a mounting foot of the first lens, the amount of heat absorbed via the relevant mounting foot of the second lens is reduced, and thus also the amount of heat that can be transferred to the second lens.The invention is based on the realization that the advantage resulting from a support foot arranged in a shaded area outweighs the disadvantage associated with a concentrated introduction of mechanical or thermal loads in certain angular positions.

[0010] The projection lens can comprise a plurality of first support feet, with the first support feet collectively carrying the first lens. The projection lens can comprise a plurality of second support feet, with the second support feet collectively carrying the second lens. The projection lens can comprise a plurality of third support feet, with the third The support feet together bear the third lens. Bearing means that the weight of one lens is transferred to the frame via the support feet. The support feet bearing one lens can be mounted on the frame in a plane, particularly a horizontal plane. The plane in which the support feet are mounted on the frame can correspond to the plane in which the lens supported by the support feet extends, or to a plane parallel thereto. In the context of this patent application, directional terms refer to a state in which the projection lens is in its intended operation. During transport to the place of intended operation, the projection lens may have a different orientation. Preferably, care is taken during transport to ensure that the orientation of the projection lens changes as little as possible.

[0011] The projection lens can be designed such that a plurality of secondary support feet are arranged at an angular position that corresponds to the angular position of a primary support foot. The projection itself can be designed such that every second support foot is arranged at an angular position that corresponds to the angular position of a primary support foot.

[0012] The projection lens can comprise a plurality of third lenses, wherein for each pair of third lenses, each mounting foot is arranged in an angular position in which no other mounting foot of the pair is arranged. The projection lens can comprise at least two third lenses, preferably at least five third lenses, and more preferably at least ten third lenses.

[0013] Each retaining foot can include a support surface through which the weight of the supported lens is transferred to the retaining foot. The bearing surface can be positioned below the supported lens, so that the weight force exerted by the supported lens acts in the direction of the bearing surface. The bearing surfaces of several supports that jointly hold a lens can span an area that is complementary to the supported lens. The supported lens can then be positioned so that different surface areas of the lens rest on the bearing surfaces of different supports.

[0014] A plurality of mounting feet, all supporting a single lens, can be uniformly distributed around the circumference of the projection lens. This means that with n mounting feet, there is an angular difference of 360° / n between the angular positions of any two adjacent mounting feet. The angular difference is measured between two rays emanating from a central axis of the projection lens and extending along the shortest path towards the two mounting feet. Each of the rays forms a right angle with the central axis. The central axis can coincide with the optical axis of the projection lens.

[0015] To fix the position of a lens relative to the frame, an adhesive bond can be used between the lens and a support base that holds the lens. In one embodiment, each support base holding the first lens is connected to the first lens via an adhesive bond. This can be applied to one, several, or all lenses of the projection lens.

[0016] Adhesives whose properties are favorable for this application often have poor resistance to DUV radiation. To prevent degradation of the adhesive bond during operation of the projection lens, the projection lens can be designed in such a way that... that the adhesive bond is protected from incoming DUV radiation. The projection objective can include a protective layer positioned in the DUV beam path such that the DUV radiation cannot reach any of the adhesive bonds. The protective layer can be formed by a separate component or be incorporated into a separate component. In one embodiment, the protective layer is located between the lens and the adhesive bond. The protective layer can be formed by a coating applied to a surface of the lens. This surface can be a surface of the lens facing the adhesive bond.

[0017] The protective layer can be designed to absorb DUV radiation. Heat generated by absorption can be transferred to adjacent structures, in particular to a lens adjacent to the protective layer and / or to an adhesive bond adjacent to the protective layer.

[0018] If a protective coating applied to a lens surface extends in the form of a continuous ring around the optical axis of the lens, heat is applied uniformly across the lens's circumference. However, heat is also supplied to the lens in areas where there is no adhesive bond that needs protection from DUV radiation. Therefore, more heat is supplied to the lens than would be necessary to protect the adhesive bond.

[0019] The invention proposes to design the protective layer as a local protective layer, such that the protective layer exists only in those areas of the projection lens where an adhesive bond actually needs to be protected from DUV radiation. With respect to the optical axis of a lens, this can be between two angular positions. The enclosed first angular region includes a protective layer on a lens to protect an adhesive bond. The protective layer can be designed to completely cover the adhesive bond, so that no part of the EUV beam path can reach the adhesive bond without passing through the protective layer.

[0020] Adjacent to the first angular region, there may be a second angular region in which no protective layer is formed on the lens. This second angular region may be bounded by another protective layer intended to protect a different adhesive bond. The second angular region may be at least twice as large, preferably at least five times as large, and more preferably at least ten times as large as the first angular region. Angular regions are compared based on the angle over which they extend. An angular region extending over 10° is twice as large as an angular region extending over 5°.

[0021] Such a ratio between the first angular region and the second angular region can apply to any combination of a protective layer and an adjacent area free of protective layer on a lens. In this way, the heat input into a lens can be significantly reduced compared to a conventional ring-shaped protective layer.

[0022] The projection lens can be designed such that, viewed in the direction of the DUV beam path, the second lens is positioned behind the first lens. The second lens can follow directly after the first lens, so that no further lenses of the projection lens are positioned between the second and first lenses. Alternatively, it is also possible that a [missing information - likely a specific element] is positioned between the first and second lenses. or several further lenses of the projection lens are arranged. The further lenses can be third lenses within the meaning of the invention, in which one or more or all of the support feet are arranged in an angular position in which no support foot of the first lens and no support foot of the second lens is arranged.

[0023] If a second support foot is shaded by a first support foot, a separate protective layer to shield the second support foot from DUV radiation is not strictly necessary. The second support foot can therefore be free of a directly associated protective layer. Alternatively, it is also possible for the second support foot to be provided with a directly associated protective layer.

[0024] Each support foot of the second lens can be shaded by a support foot of the first lens. The number of support feet of the first lens can be identical to the number of support feet of the second lens. It is also possible that the number of support feet of the first lens is greater than the number of support feet of the second lens. In particular, the number of support feet of the first lens can be a multiple of the number of support feet of the second lens.

[0025] In other embodiments, the number of mounting feet of the second lens can be greater than the number of mounting feet of the first lens. In this case, some mounting feet of the second lens may be shaded by mounting feet of the first lens, while others may be exposed to DUV radiation without shading. Mounting feet of the second lens that are not shaded by mounting feet of the first lens may be protected with a local protective coating.

[0026] With respect to the direction of the DUV beam path, one or more lenses of the projection lens can be arranged in front of the first lens. One, several, or all of these lenses can be third lenses within the meaning of the invention, in which each mounting foot is arranged in an angular position in which neither a mounting foot of the first lens nor a mounting foot of the second lens is located.

[0027] With respect to the direction of the DUV beam path, one or more lenses of the projection lens can be arranged behind the second lens. One, several, or all of these lenses can be third lenses within the meaning of the invention, in which each mounting foot is arranged in an angular position so that neither a mounting foot of the first lens nor a mounting foot of the second lens is present.

[0028] The projection objective can comprise a first pair consisting of a first lens and a second lens, and a second pair consisting of a first lens and a second lens. The first and second pairs can be arranged one behind the other, such that, viewed along the DUV beam path, the first lens of the second pair is located behind the second lens of the first pair. Alternatively, the first and second pairs can be entangled, with the first lens of the second pair positioned between the first and second lenses of the first pair.

[0029] The projection object can comprise at least 10 lenses, preferably at least 15 lenses, which define the imaging beam path between the object plane and the image plane. The lenses can be arranged one behind the other, so that the DUV beam path passes through each of the lenses sequentially.

[0030] DUV radiation refers to electromagnetic radiation with a wavelength shorter than that of visible light, but not so short that it cannot pass through the material of a lens. The wavelength of DUV radiation can range from 150 nm to 400 nm. The projection lens can be designed to operate with DUV radiation at wavelengths of 193 nm, 248 nm, or 365 nm.

[0031] The invention is described below by way of example with reference to the accompanying drawings and advantageous embodiments. The drawings show: Fig. 1: a schematic representation of a microlithographic projection exposure system; Fig. 2: a schematic representation of the projection lens of the reaction exposure system from Fig. 2; Fig. 3: a detail of the projection lens from Fig. 2 in an enlarged sectional view; Fig. 4: the detail from Fig. 3 in a top view; Fig. 5: a schematic representation of a lens of the Projection lens from Fig. 2; Figs. 6-8: schematic representations of various lenses of the projection lens from Fig. 2; Figs. 9-10: schematic representations of a first lens and a second lens of the projection lens from Fig. 2; Figs. 11-12: the view according to Fig. 2 in alternative embodiments of the invention.

[0032] Figure 1 schematically depicts a microlithographic DUV projection exposure system. The projection exposure system comprises an exposure radiation source 14, an illumination system 10, and a projection object 22. The exposure radiation source 14 generates electromagnetic radiation in the DUV range with a wavelength between 150 nm and 400 nm. The radiation emitted by the exposure radiation source 14 is captured by the illumination system 10 and shaped into an illumination beam path 16, so that an object field in an object plane 12 is illuminated with uniform radiation intensity.

[0033] A photomask 13 is arranged in the object plane 12. The radiation passing through the photomask 13 strikes the projection lens 22, which defines an imaging beam path 17 by which the photomask 13 is imaged onto an image plane 21. An image of a structure formed on the photomask 13 is created in the image plane 21. A lithographic object in the form of a wafer 15 is arranged in the image plane 21. The structure formed on the photomask 13 is transferred to a radiation-sensitive layer of the wafer 15, so that structuring of the wafer 15 can take place in subsequent steps. The photomask 13 is carried by a first scanning device 18, and the wafer 15 is carried by a second scanning device 19. The exposure of the wafer 20 takes place in a scanning process in which the photomask 13 and the wafer 20 are moved synchronously together by the scanning devices 18, 19.

[0034] According to Fig. 2, the projection lens 22 comprises a larger number of lenses 20A-J, 24, 25, which are supported by a frame device 23. The lenses 20A-J, 24, 25 are The frame 23 is aligned coaxially to an optical axis 29. It extends around the optical axis 29. Each of the lenses 20A-J, 24, 25 is attached to the frame 23 by a plurality of mounting feet 26A-26H, 46A-46H, 47A-47H. Figures 3 and 4 show, by way of example, a mounting foot 26A of the uppermost lens 20A attached to the frame 23.

[0035] The mounting base 26A comprises a contact surface 38 pointing towards the lens 20A. The contact surface 38 is inclined and oriented to match the lens 20A. The first lens 20A is attached to the contact surface 38 of the mounting base 26A via an adhesive bond 27. The adhesive bond 27 is covered by a local protective layer 28, see Fig. 4. The local protective layer 28 is applied to the underside of the lens 20A, with the extent of the local protective layer 28 being dimensioned such that it just covers the adhesive bond 27. The function of the local protective layer 28 is to shield the adhesive bond 27 from DUV radiation passing through the lens 20A. The adhesive bond 27 is thus protected from damage that would occur if the DUV radiation were to strike the adhesive bond 27 directly.

[0036] The DUV radiation is absorbed in the local protective layer 28, generating heat. This heat is transferred to the structures surrounding the local protective layer 28, specifically to the lens 20A and the adhesive bond 27. Since a heat input to the lens 20A is generally undesirable, the local protective layer 28 is kept as small as possible so that only the DUV radiation that would otherwise reach the adhesive bond 27 is blocked. The surface area of ​​the lens 20A through which the DUV radiation can pass unhindered should be as large as possible.

[0037] As shown in Fig. 5, in this embodiment, the lens 20A is supported by eight mounting feet 26A-26H distributed around the circumference of the first lens 24. A first axis 31 and a second axis 32 are shown, which, together with the optical axis 29, define a Cartesian coordinate system. Within the plane of the axes 31, 32, each of the mounting feet 26A-26H can be assigned an angular position 30, with the 0° angular position being arbitrary. In Fig. 5, mounting foot 26A is in the 0° position, mounting foot 26C in the 90° position, mounting foot 26E in the 180° position, and mounting foot 26G in the 270° position. The angular position 30 of mounting foot 26B is 45°. The eight support feet 26A-26H are evenly distributed over the circumference of the first lens 24 with an angular difference of 45° between the angular positions 30 of two adjacent support feet.

[0038] Each mounting foot 26A-26H is assigned a local protective layer 28 to protect the adhesive bond 27. These local protective layers 28 are distributed across eight positions around the circumference of the lens 20A, where the lens 20A receives an increased amount of heat. The areas where the lens 20A is provided with a local protective layer 28 are as small as possible relative to the surface area of ​​the lens 20A. Figure 5 shows that a first angular region 48, within which a local protective layer 28 is applied, is significantly smaller than an adjacent second angular region 49, which is free of a protective layer. This locally distributed heat input is accompanied by thermal deformation, which is generally associated with a reduction in image quality.Within the scope of the invention, it is possible to design the geometric shape of the first lens 24 in such a way that a desired target shape of the first lens 24 is achieved with a heat distribution expected during the operation of the projection exposure system.

[0039] Figures 6-8 show lens 20A, lens 20B, lens 20A, lens 20B, lens 24, lens 24, lens 20A, lens 20B, lens 24, lens 20A, arranged in the first position within the projection object 22. Lens 24, arranged in the third position within the projection object 22, is a first lens according to the invention. Each of the lenses 20A, 20B, and 24 has mounting feet 26A-26H and 46A-46H, respectively, evenly distributed around its circumference. However, the positions of the mounting feet 26A-26H and 46A-46H are rotated relative to each other, so that the angular positions 30 differ from lens to lens. If, for example, the support foot 26A of the lens 20A is arranged in a certain angular position 30, then neither of the other two lenses 20B, 24 has a support foot in this angular position 30.This distribution of the support feet 26A-26H, 46A-46H across several lenses 20A, 20B, 24 has the advantage that the heat supply to the lenses occurs at different angular positions, thus avoiding a mutual reinforcement of thermal deformations.

[0040] According to the invention, the projection object 22 comprises a first lens 24 and a second lens 25, which deviate from the conventional distribution of the support feet 26. Within the sequence of lenses 20A-20J, 24, 25 of the projection object 22, the first lens 24 and the second lens 25 follow directly one another, with the first lens 24 being in the third position and the second lens 25 in the fourth position within the overall sequence of lenses of the projection object.

[0041] For the first lens 24 and the second lens 25, the angular positions 30 are the same for all eight mounting feet 26A-26H. Within the beam path of the projection object 22, the first lens 24 and the second lens 25 are arranged such that the mounting feet 47A-47H of the second lens 25 are shaded by the mounting feet 46A-46H of the first lens 24. Due to the shading, the mounting feet 47A-47H of the second lens 25 are not exposed to direct DUV radiation, which significantly reduces the heat input to the second lens 25 compared to a conventional distribution of the mounting feet 26. This reduces the probability of a deterioration in image quality due to thermal deformation of the second lens 25.

[0042] Figure 11 shows an alternative embodiment of a projection object 22 in which the first lens 24 and the second lens 25 are not arranged directly adjacent to each other, but rather a further lens 20G is arranged between the first lens 24 and the second lens 25. The degree of vignetting between the lenses of the projection object 22 depends on details in the design of the beam path. The vignetting of a second lens 25 by a first lens 24 according to the invention can be used with any pair of lenses where a sufficient degree of vignetting is present due to the design of the imaging beam path. The lower the degree of vignetting between two lenses, the greater the likelihood that the advantages resulting from a conventional distribution of the support feet 26A-26H around the circumference of the production object will outweigh the disadvantages.

[0043] In the further embodiment shown in Fig. 12, the projection object 22 comprises a first pair of lenses 41, 42 and a second pair of lenses 43, 44, in which the shading according to the invention is used. In the first pair, lens 41 corresponds to a first lens according to the invention and lens 42 to a second lens according to the invention. In the second pair, lens 43 corresponds to a first lens according to the invention and lens 44 to a second lens according to the invention.

Claims

Patent claims 1. Microlithographic projection lens with a plurality of lenses (20A-20J, 24, 25), wherein the lenses (20A-20J, 24, 25) define an imaging beam path (17) between an object plane (12) and an image plane (21), and wherein the lenses (20A-20J, 24, 25) are designed to image a photomask (13) arranged in the object plane (12) onto a lithographic object (15) arranged in the image plane (21), and with a frame device (23), wherein support feet (26A-26H, 46A-46H, 47A-47H) are attached to the frame device (23), and wherein the lenses (20A-20J, 24, 25) are held by the support feet (26A-26H, 46A-46H, 47A-47H) are worn, wherein a first retention foot (46A-46H) supports a first lens (24), wherein a second retention foot (47A-47h) supports a second lens (25), and wherein a third retention foot (26A-26H) supports a third lens (20A-20J).wherein the first support foot (46A-46H) is attached to the frame device (23) in the same angular position (30) as the second support foot (47A-47H), and wherein the third support foot (26A-26H) is arranged in an angular position in which no first support foot (46A-46H) of the first lens (24) and no second support foot (47A-47H) of the second lens (25) is arranged.

2. Microlithographic projection lens according to claim 1, wherein the first lens (24) is supported by a plurality of first support feet (46A-46H), wherein the second lens (25) is supported by a plurality of second support feet (47A-47H), and wherein the third lens (20A-20J) is supported by a plurality of third support feet (26A-26H).

3. Microlithographic projection lens according to claim 2, wherein a plurality of second support feet (47A-47H) are arranged in an angular position (30) that corresponds to the angular position (30) of a first support foot (46A-46H).

4. Microlithographic projection lens according to claim 3, wherein every second support foot (47A-47H) is arranged in an angular position (30) that corresponds to the angular position (30) of a first support foot (46A-46H).

5. Microlithographic projection lens according to one of claims 2 to 4, wherein each third support foot (26A-26H) is arranged in an angular position (30) in which no first support foot (46A-46H) and no second support foot (47A-47H) is arranged.

6. Microlithographic projection lens according to any one of claims 1 to 5, comprising a plurality of third lenses (20A-20J) , wherein for each pair of third lenses (20A- 20J) each support foot (26A-26H) is arranged in an angular position (30) in which no other support foot (26A-26H) of the pair is arranged.

7. Microlithographic projection lens according to claim 6, comprising at least five third lenses (20A-20J) .

8. Microlithographic projection lens according to any one of claims 1 to 7, wherein each support foot (26A-26H, 46A-46H, 47A-47H) comprises a support surface (38) arranged below the supported lens (20A-20J, 24, 25).

9. Microlithographic projection lens according to one of claims 1 to 8, wherein an adhesive connection (27) is formed between the support foot (26A-26H, 46A-46H, 47A-47H) and the supported lens (20A-20J, 24, 25).

10. Microlithographic projection lens according to claim 9, comprising a protective layer (28) to shield the adhesive joint (27) from incident radiation.

11. Microlithographic projection lens according to claim 10, wherein the protective layer (28) between the lens (20A-20J, 24, 25) and the adhesive bond (27).

12. Microlithographic projection lens according to claim 10 or 11, wherein the protective layer (28) is formed by a coating applied to a surface of the lens (20A-20J, 24, 25).

13. Microlithographic projection lens according to one of claims 10 to 12, wherein the protective layer (28) is a local protective layer (28).

14. Microlithographic projection lens according to claim 13, wherein a first angular region (48) occupied by the local protective layer (28) is at least a factor of 5 larger than a second angular region (49) adjacent to the first angular region (48) which is free of a protective layer.

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