Mirror system, microlithographic projection exposure apparatus comprising mirror system

Abstract

The invention relates to a mirror system comprising an EUV mirror having an optical surface (32) with a high reflectivity for EUV radiation, and comprising a frame structure (39) carrying system components of the mirror system. The frame structure comprises a structural body (40) and an insert (42) made of a material having a thermal property different from that of the material of the structural body (40). A fluid passage (41) for a temperature control fluid is formed in the structure. The insert (42) is exposed to a thermal load during operation of the mirror system. The insert (42) spans the contour line (44) transversely to the direction of the fluid channel (41) such that a cross-sectional portion (49) of the fluid channel (41) is received within the contour line (44). The invention also relates to a microlithographic projection exposure apparatus comprising such a mirror system.

Description

[0001] This patent application claims priority to German patent application DE 10 2023 205 961.4, filed on 23 June 2023, the entire contents of which are incorporated herein by reference (“incorporated by reference”). Technical Field

[0002] This invention relates to a mirror system and a microlithography projection exposure apparatus including a mirror system. Background Technology

[0003] Microlithography projection exposure equipment is used to fabricate integrated circuits with extremely small structures. A photomask irradiated by very short-wavelength extreme ultraviolet radiation (EUV radiation) is imaged onto a lithographic object in order to transfer the mask structure onto the lithographic object.

[0004] The projection exposure apparatus contains multiple EUV mirrors, which have optical surfaces that reflect EUV radiation. The EUV mirrors are precisely defined in shape and precisely positioned to ensure that the image of the mask on the lithographic object has sufficient quality.

[0005] The desired imaging quality can only be achieved when the projection exposure apparatus includes a frame structure that holds the system components in place relative to each other with sufficient precision. During the operation of the projection exposure apparatus, various thermal loads affect its components. Heat is supplied, for example, through the absorption of EUV radiation, through heating devices, or through waste heat associated with the mechanical movement of the projection exposure apparatus components.

[0006] If the frame structure or a portion thereof heats up, thermal deformation may occur, resulting in undesirable displacement of the components of the projection exposure apparatus relative to each other. This is typically accompanied by a decrease in image quality. To avoid thermal deformation, the frame structure may be provided with fluid channels through which temperature-regulating fluid is guided during operation of the projection exposure apparatus. The temperature-regulating fluid allows heat to dissipate from the frame structure, thereby maintaining the frame structure at a desired temperature.

[0007] For frame structures in which fluid channels are formed, materials resistant to the effects of temperature-regulating fluids are preferably used, i.e., particularly non-corrosive materials. However, such materials typically have low thermal conductivity, thereby adversely affecting heat transfer to the temperature-regulating fluid. It is known to provide inserts to frame structures whose thermal properties deviate from those of the structure itself, in order to mitigate the undesirable effects of the supplied heat on the frame structure. Summary of the Invention

[0008] This invention aims to provide a mirror system and a microlithography projection exposure apparatus incorporating the mirror system, wherein the frame structure exhibits improved performance under thermal influence. This objective is achieved through the features of the independent patent claims. Advantageous embodiments are specified in the dependent claims.

[0009] The mirror system according to the invention comprises an EUV mirror and a frame structure. The EUV mirror has an optical surface with high reflectivity to EUV radiation, and the frame structure carries system components of the mirror system. The frame structure includes a body and an insert, wherein the insert is made of a material different from the material of the body. A fluid channel for temperature-regulating fluid is formed in the body. During operation of the mirror system, the insert is exposed to a heat load. The insert crosses a profile transverse to the direction of the fluid channel, such that a cross-sectional portion of the fluid channel is accommodated within the profile.

[0010] The term "insertion profile" refers to a line extending in a plane oriented transverse to the direction of the fluid channel. If there exists a straight line connecting two points of the profile such that the cross-sectional portion is enclosed between the profile and the straight line, then the cross-sectional portion of the fluid channel is considered to be contained within the profile.

[0011] In the case of the reflector system according to the invention, the structure can be made of a material with high resistance to contact with the temperature-regulating fluid, while the insert is made of a material with more favorable thermal properties than the structure material. Because the insert has a surface shape adapted to the fluid channel, and the material with favorable thermal properties is closer to the fluid channel, the heat introduced via the insert can negatively impact the frame structure to a very small extent.

[0012] In one embodiment, the insert is made of a material with higher thermal conductivity than the structure material. Because the insert conforms to the shape of the fluid channel, a larger surface area is available through which heat from the insert can be transferred to the temperature-regulating fluid. Thermal deformation of the frame structure is reduced due to the improved heat transfer to the temperature-regulating fluid.

[0013] The temperature-regulating fluid can be a temperature-regulating liquid, such as water. Suitable materials that resist permanent contact with water are, for example, high-grade steel, such as Cr steel. Aluminum alloys or ceramic materials can also be used. The material of the structure can have a low thermal conductivity, which can be, for example, less than 200 W / (K*m), preferably less than 50 W / (K*m), and more preferably less than 20 W / (K*m).

[0014] The material for the insert does not need to have special corrosion resistance. For example, copper, aluminum, ceramics, and composite materials are suitable as insert materials. The thermal conductivity of the insert material can be higher than that of the structure material. For example, the thermal conductivity of the insert material can be greater than 200 W / (K*m), preferably greater than 300 W / (K*m).

[0015] Additionally or alternatively, the insert material can have a lower coefficient of thermal expansion than the structure material. Even without improved heat transfer, a lower coefficient of thermal expansion can be beneficial because, despite heating, only small deformations occur in the frame structure. The coefficient of thermal expansion of the insert material can, for example, be less than 5 × 10⁻⁶. -6 K -1 Preferably less than 2 × 10 -6 K -1 A material with a low coefficient of thermal expansion, for example, an iron-nickel alloy known by the name Invar.

[0016] The cross-sectional portion of the fluid channel contained within the contour line can be greater than 40% of the cross-sectional area of ​​the fluid channel, preferably greater than 60%, and more preferably greater than 80%. Starting from the central axis of the fluid channel, there can be a segment of the cross-section of the fluid channel portion, wherein the fluid channel is not surrounded by the insert. The angle of extension of the segment is preferably less than 180°, more preferably less than 120°, and even more preferably less than 90°.

[0017] The contour line can be composed of multiple straight segments. Alternatively, the contour line may have a rounded shape adapted to the fluid channel. In the context of this invention, it is advantageous to have a small distance between the wall of the fluid channel and the insert. For example, this distance can be between 0.3 mm and 10 mm, preferably between 0.5 mm and 5 mm, and more preferably between 0.7 mm and 2 mm. If the distance varies along the circumference of the fluid channel, the specification relates to the minimum distance between the wall of the fluid channel and the insert.

[0018] Inserts can be obtained as finished components before being attached to the structure. The connection between the insert and the structure can be achieved using suitable joining methods. For example, the connection can be achieved through diffusion welding, other welding methods, or brazing. Adhesive bonding and other joining methods are also possible.

[0019] In an alternative embodiment, the insert of the structure can be manufactured using additive manufacturing. Material for the insert is added to the structure, resulting in the shape of the insert being formed during the additive manufacturing process. The material for the insert can be added to the structure, for example, in powder form. The solid internal structure of the material can be created, for example, by laser melting, by applying ultrasound, and / or by generating friction.

[0020] In all cases, the frame structure can be designed so that the structure performs a supporting function, meaning that the insert itself is not an independent supporting structure.

[0021] The structure can be provided with recesses that match the shape of the insert. The recesses may not have undercuts in the insertion direction. This has the advantage that, when the insert is available as a finished part, the insert can be inserted into the recess without creating cavities in the frame structure. For example, the insertion direction can be oriented perpendicular to or parallel to the fluid channel. In the case of additive manufacturing, the absence of undercuts in the direction of material accumulation also facilitates the production of the insert. The recesses can be designed to taper in the insertion direction. The taper can extend along a portion of the insertion path or the entire insertion path. In the latter case, the insert can be inserted into the structure without the need for sliding movement between the surface of the insert and the surface of the structure.

[0022] The insertion direction, or, in the case of additive manufacturing, the build direction, can be oriented transversely to the direction of the fluid channel. The insertion / build direction can also be parallel to the direction of the fluid channel. If the insertion / build direction is parallel to the fluid channel, the insert can have an undercut relative to its transverse direction, which allows the insert to be designed to wrap around the fluid channel to a more pronounced degree.

[0023] The contour line may span a plane perpendicular to the axis of the fluid channel. This plane lies within a segment of the fluid channel, in which a cross-sectional portion of the fluid channel is accommodated within the contour line. The fluid channel may include a segment extending in the longitudinal direction of the fluid channel, and in the sense of the invention, the fluid channel is accommodated within the contour line of the insert in this segment. This segment may include at least 30%, preferably at least 50%, and more preferably at least 70% of the distance the fluid channel extends within the structure.

[0024] The structure may include multiple fluid channels or multiple fluid channel sections extending within the structure. Fluid channel sections may be arranged in parallel. This is, for example, if a fluid channel section extends between an input manifold and an output manifold. Fluid channel sections arranged in series are also possible.

[0025] The insert can be designed to cover an area spanned by multiple fluid channels and / or fluid channel portions. The insert can be shaped such that each of the fluid channels and / or fluid channel portions has a cross-sectional portion accommodated within the outline of the insert. One or more features disclosed in the context of the first fluid channel can be applied to all fluid channels and / or fluid channel portions.

[0026] The structure can be a main body made of a homogeneous material, such that heat propagation within the structure is largely dependent on the material properties. To better control the thermal state of the structure, measures can be incorporated to prevent heat propagation in specific directions. For example, the structure can be provided with a heat shield that impedes heat propagation. In one embodiment, the heat shield can be configured as a cavity. Additionally or alternatively, other components, such as sensors, heating elements, or heat pipes, can be integrated into the structure. The invention also covers frame structures comprising multiple inserts. Each insert may include one or more features described in the context of a first insert.

[0027] The frame structure according to the invention can realize various functions within a microlithography projection exposure apparatus. The frame structure can be, for example, a frame structure that supports components of the illumination system of the microlithography projection exposure apparatus. In one embodiment, the frame structure supports multiple EUV mirror elements, particularly multiple EUV mirror elements of a faceted mirror, via inserts. In other words, the mirror elements are attached to the inserts such that mechanical forces from the mirror elements are introduced into the frame structure via the inserts.

[0028] The frame structure may be a frame structure that additionally or alternatively supports the projection lens of a microlithography projection exposure apparatus. For example, the frame structure may support the EUV mirror of the projection lens via an insert. An actuator may be provided that can change the position and / or orientation of the EUV mirror relative to the frame structure.

[0029] Alternatively, the frame structure can support sensors via inserts. The sensors can be designed to acquire information about the position and / or orientation of the EUV mirrors, particularly the position and / or orientation of the EUV mirrors for the projection lens. The sensors can also be designed to acquire, for example, temperature information about the local temperature of the frame structure. This temperature information can be used to estimate the expected position of the EUV mirrors.

[0030] Alternatively, the frame structure can support a heating device. The heating device can be designed to supply heat to the EUV reflector, particularly the EUV reflector of the projection lens. The heat can be directed to the EUV reflector non-contactly, particularly in the form of infrared radiation. The heating device can be attached to an insert. Specifically, the heating device can be supported by the frame structure via an insert. The insert can be surrounded by fluid channels.

[0031] The present invention also relates to a projection lens comprising a plurality of EUV mirrors for imaging a photomask onto an image plane. At least one of the EUV mirrors of the projection lens is an EUV mirror of a mirror system according to the present invention, wherein the mirror system forms part of the projection lens. The present invention also relates to an illumination system comprising a plurality of EUV mirrors for illuminating a photomask with EUV light. At least one of the EUV mirrors of the illumination system is an EUV mirror of a mirror system according to the present invention, wherein the mirror system forms part of the illumination system. The present invention also relates to a microlithography projection exposure apparatus comprising such a mirror system, such a projection lens, and / or such an illumination system. Attached Figure Description

[0032] The invention is now described by way of example with reference to the accompanying drawings, in which:

[0033] Figure 1 An embodiment of the projection exposure apparatus according to the present invention is shown;

[0034] Figure 2 An embodiment of the mirror system according to the present invention is shown;

[0035] Figure 3 The enlarged image shows the source Figure 2 Details;

[0036] Figure 4 An alternative embodiment of the invention is shown. Figure 2 Details;

[0037] Figure 5 An alternative embodiment of the invention is shown according to Figure 4 The view;

[0038] Figure 6 An alternative embodiment of the mirror system according to the invention is shown;

[0039] Figure 7 The enlarged image shows the source Figure 6 Details;

[0040] Figure 8 Another embodiment of the mirror system according to the present invention is shown;

[0041] Figure 9 The enlarged image shows the source Figure 8 Details;

[0042] Figure 10 Another embodiment of the mirror system according to the present invention is shown;

[0043] Figure 11 The enlarged image shows the source Figure 10 Details;

[0044] Figure 12 Components of a mirror system according to the invention in an alternative embodiment are shown. Detailed Implementation

[0045] Figure 1 A microlithography EUV projection exposure apparatus is schematically shown. The apparatus includes an exposure beam source 14, an illumination system 10, and a projection lens 22, which operate together within a vacuum chamber 23. During operation of the EUV projection exposure apparatus, negative pressure dominates within the vacuum chamber 23.

[0046] Exposure beam source 14 generates electromagnetic radiation in the EUV range, specifically electromagnetic radiation with wavelengths between 5 nm and 30 nm. The exposure radiation emitted from exposure beam source 14 is focused into intermediate focal plane 16 by collector 15. The exposure radiation passing through intermediate focal plane 16 is guided into object plane 12 by illumination system 10, resulting in the object field in object plane 12 being illuminated with uniform radiation intensity.

[0047] The illumination system 10 includes a deflector 17 for deflecting exposure radiation to the first faceted mirror 18. A second faceted mirror 19 is disposed downstream of the first faceted mirror 18. The second faceted mirror 19 is used to image the facets of the first faceted mirror 18 onto the object plane 12.

[0048] A photomask 13 is disposed in the object plane 12 and imaged onto the image plane 21 by multiple mirrors M1-M6 of the projection lens 22. The structure formed on the photomask 13 is transferred to the radiation-sensitive layer of the wafer 20 disposed in the image plane 21. The photomask 13 is suspended on the first scanning device 24, and the wafer 20 is stationary on the second scanning device 25, so that the wafer 20 can be exposed during the scanning process, during which the photomask 13 and the wafer 20 move synchronously with each other.

[0049] Figure 6 The display shows a mirror system in which the mirror bodies 38 of mirrors M1 to M6 are held on a frame structure 39 by an actuator 30. The actuator 30 can be used to change the position of the mirror bodies 38 relative to the frame structure 39 in order to orient and position the mirror bodies 38. An optical surface 32 for reflecting EUV radiation is formed on the mirror bodies 38.

[0050] The projection exposure apparatus includes a heating device 26, which is designed to guide infrared radiation 27 to the reflective surfaces of EUV mirrors M1-M6 of the projection lens 22 to heat the EUV mirrors 20 so that the temperature of the EUV mirrors M1-M6 reaches the target value.

[0051] Figure 2 A schematic diagram of the first faceted mirror 18 is shown. In a practically large number of EUV mirror elements, Figure 2 This shows two mirror elements 43 supported by a frame structure 39. The frame structure 39 includes a body 40 and an insert 42. Multiple fluid channels in the form of cooling channels 41 are formed in the body 40, extending through the body 40 between an inlet opening and an outlet opening. The EUV mirror elements 43 are supported by the insert 42.

[0052] During operation of the projection exposure apparatus, heat is dissipated from the EUV mirror element 43. A heat flow is generated, originating from the EUV mirror element 43 and extending directly into the cooling channel 41 via the insert 42. A cooling liquid, particularly water, is directed through the cooling channel 41. Heat is transferred to the cooling liquid via the walls of the cooling channel 41 and dissipated from the frame structure 39.

[0053] The structure 40, in which the cooling channel 41 is formed, is made of a material with good resistance to the cooling liquid. In an exemplary embodiment, the structure 40 is made of a high-grade stainless steel material with low thermal conductivity. The structure 40 may also be made of other materials, such as aluminum or ceramic. To improve heat transfer, an insert 42 is incorporated into the structure 40 and located in a recess 47 of the structure 40. The insert 42 is made of copper and therefore of a material with significantly higher thermal conductivity than the high-grade steel material of the structure 40. The copper material does not come into direct contact with the cooling liquid and therefore has no effect on the corrosion behavior of the cooling channel. According to the invention, the insert 42 is shaped such that the cooling channel 41 is accommodated as closely as possible within the recess 48 of the insert 42. The recess 48 extends along the cooling channel 41 such that a large portion of the length of the cooling channel 41 within the structure 40 lies within the recess 48.

[0054] like Figure 3 As shown in the enlarged view, the contour line 44 (shown by a thicker line) is crossed by a recess 48, such that the cross-sectional portion 49 of the cooling channel 41 is accommodated within the contour line 44. Figure 3 In the middle, the cross-sectional portion 49 is defined by a straight line 46 connecting two points of the contour line 44 to each other. The straight line 46 is located below the central axis 50 of the cooling channel 41, and is equivalent to more than half of the cross-sectional area of ​​the cooling channel 41 formed by the cross-sectional portion 49 contained within the contour line 44. Figure 3 It is also shown that the section 45 of the cooling channel 41 that is not contained within the outline 44 of the insert 42 extends at less than 180°. The distance between the wall of the cooling channel 41 and the insert 42 is less than 1 mm.

[0055] Figure 4A variation is shown in which the protruding structure of the insert 42 tapers in a wedge shape at its lower end. This taper facilitates insertion of the insert 42 into the recess of the structure 40, as the insert 42 automatically centers via the wedge-shaped surface. Figure 5 In this insertion path, the shape of the insert 42 gradually tapers. The recess 48 in the insert 42 has a circular shape, thus better fitting the cross-section of the cooling channel 41.

[0056] Figure 6 The projection lens 22 displays a mirror system in which EUV mirrors M1-M6 are held on frame structure 39. The position and orientation of EUV mirrors M1-M6 on mirror body 38 relative to frame structure 39 can be changed by actuator 30.

[0057] like Figure 6 An example based on one of the actuators 30 is schematically shown, the actuator 30 being attached to an insert 42 located in a recess of a structure 40 in a frame structure 39. According to Figure 7 In the enlarged view, similar to the aforementioned embodiment, the insert 42 has a recess adapted to a cooling channel of the structure 40. The recess spans a contour line, within which the cooling channel 41 is located. In this embodiment, the entire cross-section of the cooling channel 41 is accommodated within the contour line.

[0058] exist Figure 8 In this system, the reflector system includes a second frame structure 60 that carries the sensor 51. The position of the reflector body 38 is determined by the sensor 51. The measured value is fed to the control unit of the reflector system, allowing the control unit to control the actuator 30. The sensor 51 is held on an insert 42 that is inserted into a recess in the structure 40. Figure 9 The insert 42 spans the contour line, within which the cooling channel 41 of the structure 40 is housed. During operation of the projection exposure apparatus, the heat load exposed to the sensor 51 or the heat generated by the operation of the sensor 51 is introduced into the cooling liquid flowing through the cooling channel 41 via the insert 42, which is made of a material with high thermal conductivity.

[0059] exist Figure 10 In the illustrated embodiment, the heating device 53 is attached to the frame structure 39 and directs infrared radiation to the reflector body 38 to heat the reflector body 38. According to Figure 11 The heating device is attached to the insert 42 located in the recess of the structure 40. In a manner similar to the previous embodiment, the heat accumulated in the heating device 53 is introduced into the cooling channel 41 via the insert 42.

[0060] Figure 12One embodiment is shown, in which the frame structure 39 includes two structures 40, and a heating device 53 is arranged between the two structures 40. Each structure 40 is provided with an insert 42 that extends in a circumferential manner around a cooling channel 41 formed in the structure 40. In this way, the insert 42 crosses a contour line, within which two cooling channels 41 are accommodated. The heating device 53 is connected to the structure 40 via the insert 42, such that the heating device 53 is supported by both structures 40. Heat accumulated in the heating device 53 can be emitted to the cooling channels 41 in two directions.

Claims

1. A mirror system comprising an EUV mirror having an optical surface (32) with high reflectivity to EUV radiation, and a frame structure (39) for carrying system components of the mirror system, wherein the frame structure comprises a body (40) and an insert (42), wherein the insert (42) is made of a material whose thermal properties deviate from those of the material of the body (40), wherein a fluid channel (41) for a temperature-regulating fluid is formed in the body, wherein the insert (42) is exposed to a heat load during operation of the mirror system, and wherein the insert (42) spans a profile (44) in a direction transverse to the fluid channel (41), such that a cross-sectional portion (49) of the fluid channel (41) is accommodated within the profile (44).

2. The mirror system according to claim 1, wherein, The material of the insert (42) has a higher thermal conductivity than the material of the structure (40).

3. The mirror system according to claim 2, wherein, The thermal conductivity of the material of the structure (40) is less than 200 W / (K*m), preferably less than 50 W / (K*m), and more preferably less than 20 W / (K*m).

4. The mirror system according to claim 2 or 3, wherein, The material of the insert (42) has a thermal conductivity greater than 200 W / (K*m), more preferably greater than 300 W / (K*m).

5. The mirror system according to claim 1, wherein, The coefficient of thermal expansion of the material of the insert (42) is less than 5 × 10⁻⁶. -6 K -1 Preferably less than 2 × 10 -6 K -1 .

6. The mirror system according to any one of claims 1 to 5, wherein, The cross-sectional portion (49) of the fluid channel (41) contained within the contour line (44) is greater than 40% of the cross-sectional area of ​​the fluid channel (41), preferably greater than 60%, and more preferably greater than 80%.

7. The mirror system according to any one of claims 1 to 6, wherein, The section (45) of the cross-section of the fluid channel is not surrounded by the insert (42), wherein the section (45) extends at an angle of less than 180°, preferably less than 120°, and more preferably less than 90°.

8. The mirror system according to any one of claims 1 to 7, wherein, The distance between the wall of the fluid channel (41) and the insert (42) is between 0.3 mm and 10 mm, preferably between 0.5 mm and 5 mm, and more preferably between 0.7 mm and 2 mm.

9. The mirror system according to any one of claims 1 to 8, wherein, The insert (42) is produced by additive manufacturing.

10. The mirror system according to any one of claims 1 to 9, wherein, The structure (40) is provided with a recess (48) that is not undercut in the insertion direction.

11. The mirror system according to claim 10, wherein, The recess (48) tapers in the insertion direction.

12. The mirror system according to any one of claims 1 to 11, wherein, The fluid channel (41) is accommodated within the outline (44) of the insert (42) for at least 30%, preferably at least 50%, and more preferably at least 70% of its length in the structure (40).

13. The mirror system according to any one of claims 1 to 12, wherein, The frame structure (39) supports the heating device (53).

14. The mirror system according to any one of claims 1 to 13, wherein, The fluid channel (41) is surrounded by the insert (42).

15. A microlithography projection exposure apparatus comprising a mirror system, wherein the mirror system is implemented according to any one of claims 1 to 14.

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