DE102022213987A1 - Method for assembling an optical assembly, optical assembly and projection exposure system - Google Patents

Abstract

The invention relates to a method for assembling an optical assembly (30.x) with a base body (31) of an optical element (Mx, 117) and an attachment (38), with between the attachment (38) and the base body (31) a connecting layer (50,51,51.1,51.2) is arranged to minimize stress increases in the area of the connecting layer (50,51,51.1,51.2), comprising the following process steps: - joining the base body (31), the connecting layer (50,51, 51.1,51.2) and the attachment (38), - removal of at least one area of the optical assembly (30.x) for receiving and/or exchanging material at least in a partial area of the connecting layer (50,51,51.1,51.2).Furthermore included the invention relates to an optical assembly (30.x) with a base body (31) of an optical element (Mx, 117) and an attachment (38), with a connecting layer (50, 51) between the attachment (38) and the base body (31). ,51.1,51.2) is arranged to minimize stress increases in the area of the connection layer (50,51,51.1,51.2). The assembly (30.x) is characterized in that the connecting layer (50,51,51.1,51.2) is designed in such a way that the change in the volume of the connecting layer (50,51,51.1,51.2) changes in the event of fluctuations in the connecting layer (50,51,51.1,51.2) surrounding humidity in the range of 0% rel. Humidity up to 60% rel. Moisture is less than 5% by volume, preferably less than 2% by volume and particularly preferably 0.1% by volume.

Description

The invention relates to a method for assembling an optical assembly, an optical assembly and a projection exposure system, in particular for semiconductor lithography.

Projection exposure systems for semiconductor lithography are used to create the finest structures, especially on semiconductor components or other microstructured components. The functional principle of the systems mentioned is based on using a generally reducing image of structures on a mask, with a so-called reticle, on an element to be structured with photosensitive material, a so-called wafer, in order to produce the finest structures down to the nanometer range . The minimum dimensions of the structures created depend directly on the wavelength of the light used for imaging, the so-called useful light. In addition to the predominantly used light sources with an emission wavelength in the range from 100 nm to 300 nm, the so-called DUV range, light sources with an emission wavelength in the range of a few nanometers, for example between 1 nm and 120 nm, in particular in the range of 13, have recently been increasingly used .5 nm used. The wavelength range described is also referred to as the EUV range.

The optical elements used for imaging for the application described above must be positioned and/or, if necessary, deformed with the highest precision in order to be able to guarantee sufficient imaging quality. In particular, optical elements designed as mirrors are set up in addition to positioning in up to six degrees of freedom so that the optical effective surface can be deformed. The optical effective surface is that surface of an optical element which is exposed to radiation used for imaging and exposure during normal operation of the associated system.

The deformation mentioned is brought about, for example, by actuators arranged on the rear side of the mirror opposite the optical effective surface. The actuators used can in principle act on the optical element parallel to the optical effective surface, but also perpendicular to it. A corresponding arrangement is in the German patent application DE 10 2020 210 773 A1 shown. The cited document discloses an optical element in which actuators apply forces perpendicular to the optical effective surface from the back of the optical element. The connection of the actuators to the back of the optical element is usually made via an adhesive connection, which on the one hand ensures a flat connection to minimize stress increases in the contact zone of the components due to shape tolerances and surface roughness and on the other hand transfers the forces from the actuator to the optical element.

However, adhesive connections have the disadvantage that they swell or shrink due to environmental influences, in particular changes in air humidity, as a result of which parasitic deformations can be introduced into the optical element, so that the requirements for imaging quality, in particular for the latest generations of projection exposure systems, can no longer be adequately fulfilled.

The object of the present invention is to provide a method for assembling an assembly in which the disadvantages associated with an adhesive connection are avoided. A further object of the invention is to provide a correspondingly improved optical assembly.

This task is solved by a method and a device with the features of the independent claims. The subclaims relate to advantageous developments and variants of the invention.

• - Fügen des Grundkörpers, der Verbindungsschicht und des Anbauteils,
• - Auslagerung mindestens eines die Verbindungsschicht mindestens teilweise umfassenden Bereichs der optischen Baugruppe zur Aufnahme von Material mindestens in einem Teilbereich der Verbindungsschicht.

A method according to the invention for connecting a base body of an optical element and an attachment part of an optical assembly, wherein a connecting layer is arranged between the attachment part and the base body to minimize stress increases in the area of the connection layer, comprises the following method steps:

• - joining the base body, the connecting layer and the add-on part,
• - Removal of at least one area of the optical assembly that at least partially encompasses the connecting layer to accommodate material in at least a partial area of the connecting layer.

The joining can in particular include screwing or clamping between the base body and the add-on part. Furthermore, the attachment and the base body can be at least pre-adjusted during joining, i.e. aligned with one another, with readjustment, i.e. a change in the position of the attachment to the base body, after and/or during the removal step also being conceivable.

The above-described outsourcing of the area at least partially comprising the connecting layer includes a structural change of at least parts of the connecting layer, through which the mechanical properties of the connecting layer created are improved with regard to its planned use.

In particular, at least one physical property of the connecting layer can change at least in a region of the connecting layer close to the surface due to the absorption of material. This can advantageously increase, for example, the hardness and/or the rigidity, which depends on the modulus of elasticity. This has the advantage that a material of the connecting layer that is still ductile during joining to reduce the stress increases becomes harder or stiffer and therefore less flexible, at least in this area, i.e. on the contact surfaces between the connecting layer and the base body or the add-on part. The change in physical properties can be brought about, for example, by nitriding, diffusion hardening or case hardening or any other process that involves diffusion processes and/or recrystallization processes.

The surface can thereby distribute forces acting locally on it over a larger area of the ductile region of the connecting layer underneath it and thereby advantageously minimize the predominantly plastic deformation of the connecting layer in a ductile material. The ductile material cannot be further plastically deformed by the hard shell created in this way, whereby the force of the actuator to deform the base body can be transferred to it without loss due to the deformation of the ductile connecting layer.

Particularly in the case of connecting layers, which are designed as, for example, separate, cylindrical components, the force flow can run within the harder surface, so that deformation of the underlying area does not come into play. Ideally, the connecting layer can harden completely during the aging step, whereby a material with a reduced tendency to plastic deformation can be produced from a material that is ductile during joining to minimize stress increases after the aging step, which is not plastically deformed even under normal operational loads , whereby the mechanical tensions in the connecting layer and thus in the components can be advantageously minimized.

In a further embodiment, the connecting layer can be formed at least in two parts before joining. As a result, production and/or assembly can be advantageously simplified, for example by dividing complex geometries into two simpler geometries that are easier to manufacture and also easier to assemble thanks to a suitable contact surface.

In particular, the at least two parts of the connecting layer can comprise different materials. This has the advantage that the physical properties of the connecting layer depend on the material or the surface quality of the base body, which has, for example, quartz glass or silicate glass and has a smooth surface, and the add-on part, which includes, for example, a ceramic or a metal and has a rougher surface. can be adjusted.

Furthermore, the materials can interact with each other during storage. An interaction can take place, for example, in thermocompression bonding, whereby a combination of heat and/or pressure causes diffusion, i.e. an exchange of material, between the two layers. Other possible processes that support interaction are eutectic joining or solid-liquid interdiffusion bonding. Eutectic joining has the special property that the two, mostly pure, starting materials have a higher melting point than the eutectic alloy created from them. As a result, after a first contact and formation of the eutectic alloy, which is also referred to as a eutectic, by diffusion, the connecting layer can be liquefied at a suitable temperature, whereby the gaps created by the surface roughness in the contact surface between the base body and the connecting layer and between the connecting layer and Attachment can be advantageously closed. In addition, the stiffness, strength and hardness can also change from ductile behavior to elastic behavior with higher rigidity after bonding. Furthermore, the connecting layer can form a cohesive connection through the material exchange, which can also transmit tensile forces.

In particular, the different materials can include gold and indium or copper and tin or gold and tin, which can be suitable, for example, for the eutectic joining described above.

Furthermore, joining can take place without force. In this context, force-free means that the components (base body, add-on part) do not experience any external force, as is the case with thermocompression bonding, i.e. a maximum of the weight of one component acts on the contact surfaces between the components and the connecting layer. The force-free joining has the advantage that the risk of damage to the attachment or the base body, which may have a brittle material such as glass or ceramic, for example, can be minimized.

In a further embodiment, the two parts of the connecting layer can be designed as coatings on the base body and on the add-on part. In contrast to a connecting layer designed as a separate component, the coating can achieve a firm connection that also transmits tensile forces between the coatings acting as a connecting part and the base body or the add-on part. With a suitable choice of material for the two-part connecting layer and a corresponding aging step, a connection that transmits compressive forces and tensile forces can be created between the base body and the attachment without the risk of excessive stress in the contact point.

An optical assembly according to the invention with a base body of an optical element and an attachment, wherein a connecting layer is arranged between the attachment and the base body to minimize stress increases in the area of the connection layer, is characterized in that the connection layer is designed in such a way that the change in the Volume of the connecting layer with fluctuations in the humidity surrounding the connecting layer in the range of 60% rel. Humidity up to 0% rel. Moisture is less than 5% by volume, preferably less than 2% by volume and particularly preferably less than 0.1% by volume. Particularly in the case of an EUV projection exposure system, which is usually operated in a high vacuum of 10Pa, the differences between the operation and the assembly or ventilation of the EUV projection exposure system required for maintenance can be significant. The stability of the connecting layer in the specified area prevents the high-precision optical elements from straining due to the changing environmental conditions, which results in a time-varying deformation of an optical effective surface, i.e. the surface which is exposed to the electromagnetic radiation used for the imaging, which is disruptive to the imaging quality can be advantageously avoided.

In a first embodiment, the connecting layer can be designed as a separate component. The connecting layer is placed between the base body and the add-on part when joining and can, for example, use ductile properties to advantageously compensate for the stress increases that occur due to manufacturing tolerances.

In a further embodiment, the connecting layer can be formed as a coating. This has the advantage that a connecting layer that is thin compared to the separate component can be realized and that this can already be firmly connected to the base body or the add-on part, which is achieved by a suitable coating technology, such as Chemical Vapor Deposition (CFD), Physical Vapor Deposition ( PVD), galvanic coating processes, flame spraying or thermal coating. The thickness of the connecting layer can be chosen such that by filling the bumps or valleys between the tips of the microscopically rough surface of the uncoated component, there is a surface contact between the base body and the attachment of at least 50%, preferably 60% and particularly preferably of 70% or more can be ensured, whereby the voltage increases can be sufficiently reduced. The flat contact, which is made up of direct contact between the tips of the surfaces of the base body and the add-on part and the connecting layer filling the valleys, can also ensure a stable connection under the loads that occur during operation, i.e. with no or only minimal further plastic deformation. This also applies to optical assemblies that do not undergo any further aging step after joining and coatings made of materials that do not show any changes in physical properties during a possible aging step.

Furthermore, the connecting layer can be designed as a coating arranged on the base body and a coating on the add-on part.

In particular, the two coatings can comprise different materials. This has the advantage that materials that correspond well to the materials of the base body and the add-on part can be used, i.e. have good connection properties, for example. Furthermore, at least in a partial area of the connecting layer, for example through an aging step carried out after joining, as already explained above, an alloy can be produced from the two materials which have developed physical properties that are advantageous for operation, such as dimensional stability and / or high can have stiffness.

Furthermore, the connecting layer can be non-positively connected to the base body and/or the dismantling part. In this context, non-positive means a connection that can transmit compressive forces and tensile forces. Depending on the method used, the connection can also be described as microscopically positive. The materials of the two coatings can, for example, bond together through thermocompression bonding through diffusion and heat in such a way that the newly formed grain boundaries interlock, i.e. form a positive fit, so that there is no longer a sharp separating layer.

A projection exposure system according to the invention can comprise an optical assembly according to one of the embodiments described above.

• 1 schematisch im Meridionalschnitt eine Projektionsbelichtungsanlage für die EUV-Projektionslithografie,
• 2 schematisch im Meridionalschnitt eine Projektionsbelichtungsanlage für die DUV-Projektionslithografie,
• 3a-c eine erste Ausführungsform der Erfindung,
• 4a-d weitere Ausführungsformen der Erfindung, und
• 5a-d Details der Erfindung.

Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. Show it

• 1 schematically in meridional section a projection exposure system for EUV projection lithography,
• 2 schematically in meridional section a projection exposure system for DUV projection lithography,
• 3a-c a first embodiment of the invention,
• 4a-d further embodiments of the invention, and
• 5a-d Details of the invention.

Below we will initially refer to the 1 The essential components of a projection exposure system 1 for microlithography are described as an example. The description of the basic structure of the projection exposure system 1 and its components are not intended to be restrictive.

One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a radiation source 3, lighting optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the other lighting system. In this case, the lighting system does not include the light source 3.

A reticle 7 arranged in the object field 5 is illuminated. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced in particular in a scanning direction via a reticle displacement drive 9.

In the 1 A Cartesian xyz coordinate system is shown for explanation. The x direction runs perpendicular to the drawing plane. The y-direction is horizontal and the z-direction is vertical. The scanning direction is in the 1 along the y direction. The z direction runs perpendicular to the object plane 6.

The projection exposure system 1 includes projection optics 10. The projection optics 10 is used to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0 ° is also between the object plane 6 and the Image level 12 possible.

A structure on the reticle 7 is imaged on a light-sensitive layer of a wafer 13 arranged in the area of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced in particular along the y direction via a wafer displacement drive 15. The displacement, on the one hand, of the reticle 7 via the reticle displacement drive 9 and, on the other hand, of the wafer 13 via the wafer displacement drive 15 can take place in synchronization with one another.

The radiation source 3 is an EUV radiation source. The radiation source 3 emits in particular EUV radiation 16, which is also referred to below as useful radiation, illumination radiation or illumination light. The useful radiation in particular has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example an LPP source (Laser Produced Plasma) or a DPP source. Source (Gas Discharged Produced Plasma, plasma produced by gas discharge). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

The illumination radiation 16, which emanates from the radiation source 3, is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and/or hyperboloid reflection surfaces. The at least one reflection surface of the collector 17 can be in grazing incidence (Grazing Incidence, GI), i.e. with angles of incidence greater than 45° compared to the normal direction of the mirror surface, or in normal incidence (Normal Incidence, NI), i.e. with angles of incidence smaller than 45°. with the lighting radiation 16 are applied. On the one hand, the collector 17 can be used to optimize its reflectivity for the useful radiation and on the other hand, be structured and/or coated to suppress false light.

After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focus plane 18. The intermediate focus plane 18 can represent a separation between a radiation source module, having the radiation source 3 and the collector 17, and the illumination optics 4.

The lighting optics 4 comprises a deflection mirror 19 and, downstream of it in the beam path, a first facet mirror 20. The deflection mirror 19 can be a flat deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be designed as a spectral filter which separates a useful light wavelength of the illumination radiation 16 from false light of a wavelength that deviates from this. If the first facet mirror 20 is arranged in a plane of the illumination optics 4, which is optically conjugate to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 includes a large number of individual first facets 21, which are also referred to below as field facets. Of these facets 21 are in the 1 just a few are shown as examples.

The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 21 can be designed as flat facets or alternatively as convex or concave curved facets.

Like, for example, from the DE 10 2008 009 600 A1 is known, the first facets 21 themselves can also each be composed of a large number of individual mirrors, in particular a large number of micromirrors. The first facet mirror 20 can in particular be designed as a microelectromechanical system (MEMS system). For details see the DE 10 2008 009 600 A1 referred.

Between the collector 17 and the deflection mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction.

A second facet mirror 22 is located downstream of the first facet mirror 20 in the beam path of the illumination optics 4. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the lighting optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006/0132747 A1 , the EP 1 614 008 B1 and the US 6,573,978 .

The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

The second facets 23 can also be macroscopic facets, which can have, for example, round, rectangular or even hexagonal edges, or alternatively they can be facets composed of micromirrors. In this regard, reference is also made to the DE 10 2008 009 600 A1 referred.

The second facets 23 can have flat or alternatively convex or concave curved reflection surfaces.

The lighting optics 4 thus forms a double faceted system. This basic principle is also known as the honeycomb condenser (fly's eye integrator).

It may be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the pupil facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as is the case, for example, in FIG DE 10 2017 220 586 A1 is described.

With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5.

In a further embodiment of the illumination optics 4, not shown, transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the lighting optics 4. The transmission optics can in particular have one or two mirrors for vertical incidence (NI mirror, normal incidence mirror) and/or one or two mirrors for grazing Incidence (GI mirror, Gracing Incidence mirror).

The lighting optics 4 has the version in the 1 is shown, after the collector 17 exactly three mirrors, namely the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

In a further embodiment of the lighting optics 4, the deflection mirror 19 can also be omitted, so that the lighting optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or with the second facets 23 and a transmission optics is generally only an approximate image.

The projection optics 10 comprises a plurality of mirrors Mi, which are numbered consecutively according to their arrangement in the beam path of the projection exposure system 1.

At the one in the 1 In the example shown, the projection optics 10 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 are double-obscured optics. The projection optics 10 has an image-side numerical aperture that is larger than 0.5 and which can also be larger than 0.6 and which can be, for example, 0.7 or 0.75.

Reflection surfaces of the mirrors Mi can be designed as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. The mirrors Mi, just like the mirrors of the lighting optics 4, can have highly reflective coatings for the lighting radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 10 has a large object image offset in the y direction between a y coordinate of a center of the object field 5 and a y coordinate of the center of the image field 11. This object image offset in the y direction can be approximately like this be as large as a z-distance between the object plane 6 and the image plane 12.

The number of intermediate image planes in the x and y directions in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, can be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions are known from US 2018/0074303 A1 .

One of the pupil facets 23 is assigned to exactly one of the field facets 21 to form an illumination channel for illuminating the object field 5. This can in particular result in lighting based on Köhler's principle. The far field is broken down into a large number of object fields 5 using the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 assigned to them.

The field facets 21 are each imaged onto the reticle 7 by an assigned pupil facet 23, superimposed on one another, in order to illuminate the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by overlaying different lighting channels.

The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by an arrangement of the pupil facets. By selecting the illumination channels, in particular the subset of the pupil facets that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the lighting setting.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

Further aspects and details of the illumination of the object field 5 and in particular the entrance pupil of the projection optics 10 are described below.

The projection optics 10 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 10 cannot regularly be illuminated precisely with the pupil facet mirror 22. In an image of the projection optics 10, which is the center of the Pupil facet mirror 22 images telecentrically onto wafer 13, the aperture rays often do not intersect at a single point. However, an area can be found in which the pairwise distance of the aperture beams becomes minimal. This surface represents the entrance pupil or a surface conjugate to it in local space. In particular, this surface shows a finite curvature.

It may be that the projection optics have 10 different positions of the entrance pupil for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

At the in the 1 As shown in the arrangement of the components of the illumination optics 4, the pupil facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The field facet mirror 20 is tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the deflection mirror 19.

The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the second facet mirror 22.

2 shows schematically in meridional section another projection exposure system 101 for DUV projection lithography, in which the invention can also be used.

The structure of the projection exposure system 101 and the principle of imaging is comparable to that in 1 Structure and procedure described. The same components are opposite each other by 100 1 raised reference numerals denote the reference numerals in 2 So start with 101.

In contrast to one like in 1 Due to the longer wavelength of the DUV radiation 116 used as useful light in the range from 100 nm to 300 nm, in particular from 193 nm, in the DUV projection exposure system 101 refractive, diffractive and / or reflective optical elements 117, such as lenses, mirrors, prisms, end plates and the like can be used. The projection exposure system 101 essentially comprises an illumination system 102, a reticle holder 108 for holding and precisely positioning a reticle 107 provided with a structure, through which the later structures on a wafer 113 are determined, and a wafer holder 114 for holding, moving and precisely positioning this wafer 113 and a projection lens 110, with a plurality of optical elements 117, which are held via mounts 118 in a lens housing 119 of the projection lens 110.

The illumination system 102 provides DUV radiation 116 required for imaging the reticle 107 on the wafer 113. A laser, a plasma source or the like can be used as the source for this radiation 116. The radiation 116 is shaped in the illumination system 102 via optical elements in such a way that the DUV radiation 116 has the desired properties in terms of diameter, polarization, shape of the wavefront and the like when it hits the reticle 107.

The structure of the subsequent projection optics 101 with the lens housing 119 does not differ in principle from that in, except for the additional use of refractive optical elements 117 such as lenses, prisms, end plates 1 Structure described and will therefore not be described further.

3a shows a sectional view of an optical assembly 30.1 with a mirror Mx, 117, as shown, for example, in one in the 1 and in the 2 explained projection exposure systems 1, 101 is used. The mirror Mx, 117 comprises a base body 31 with an optical effective surface 32 and is mounted on two bearings 43 on the rear side 33 opposite the optical effective surface 32. The optical assembly 30.1 further comprises attachments designed as unidirectional actuators 40, the actuators 40 being arranged in recesses 34.1 arranged on the back 33 of the base body 31. The actuators 40 act on levers 42, which are formed by the recesses 34.1 on the back 33 of the base body 31 and thereby generate a moment in the base body 31, which causes a deformation of the optical effective surface 32. The actuators 40 are connected at their ends to the levers 42 via a connecting layer 50 according to the invention. Due to its ductile behavior, the connecting layer 50 brings about optimal surface contact between the actuator 40 and the recesses 34.1 to minimize stress increases in the contact surfaces of actuators 40 and levers 42 as a result of shape tolerances and surface roughness. The connecting layer 50 also has the advantage that its physical properties, such as volume, modulus of elasticity or hardness, are below those specified Assembling the optical assembly 30.1, changes in the environmental conditions that occur, such as temperature and humidity, do not show any changes that are significant for the function.

The connecting layer 50 can include, for example, aluminum, palladium, gold, indium, copper, tin or combinations thereof, as well as other ductile metals or metal alloys. However, it can alternatively or additionally also comprise a plastic, such as a polymer.

The connecting layer 50 can also be designed either as a separate component or as a coating 51 on the actuator 40 and/or the base body 31. In addition, the connecting layer 50 can change its physical properties by an aging step following the assembly of the actuator 40, so that, for example, the ductility that is useful for assembly to compensate for the shape tolerances due to plastic deformation is minimized by the aging step, i.e. a less ductile and therefore harder material and/or a material with a higher modulus of elasticity is produced.

Variants for arranging the connecting layer 50 as a separate component and/or in the form of a coating 51 and methods for changing the physical properties are based on 5a until 5d explained in more detail.

3b shows a detail of a further optical assembly 30.2, which includes a mirror Mx, 117 and an actuator unit 49. The actuator unit 49 has a back plate 44 with counter bearings 45 and two actuators 40, the two actuators 40 being connected on one side to the counter bearings 45 and on the other side with a lever 42 connected to the back 33 of the base body 31 via a connecting layer according to the invention 50 are connected. The lever 42 can also be connected to a connecting layer 50 according to the invention or alternatively to an adhesive or can preferably be monolithic. The back plate 44 is connected to a frame 47, which faces a bearing 43 ( 3a) of the mirror Mx, 117 is decoupled to minimize the transmission of mechanical vibrations, which are caused, for example, by the reaction forces of the actuators 40.

3c shows a further optical assembly 30.3, which also has actuators 48 for deforming the optical effective surface 32 of the mirror Mx, 117. The mirror Mx, 117 comprises a cup-shaped optical body 37 with the optical effective surface 32 and a base body 31, the base body 31 being connected radially to the inner surfaces of the cup-shaped optical body 37. The base body 31 includes recesses 34.2 in which the actuators 48 are arranged, which are connected radially, i.e. over their circumference, to the recesses 34.2 via a connecting layer 50 according to the invention. In this case, the connecting layer 50 is designed in such a way that it can transmit tensile forces and shear forces in addition to compressive forces. Alternatively, the recesses 34.2 can also be conical, with the connecting layer 50 being plastically deformed to different degrees to compensate for tolerances during the assembly of the actuators 48 and the physical properties being changed in an outsourcing step already explained above to better absorb the reaction forces of the actuators 48 (See also 4b and 4d ).

The 4a until 4d show further embodiments of optical assemblies 30.4, 30.5, 30.6, 30.7. All illustrated embodiments of the optical assemblies 30.4, 30.5, 30.6, 30.7 include ring actuators 41.1, 41.2, 41.3, which differ only in the design of the contact surface for connection to the base body 31. While the actuators in the 4a (inner surface) and the 4c (outer surface) have a cylindrical contact surface, the contact surface is in the 4b (inner surface) and the 4d (outer surface) conical. A connecting layer 50 according to the invention is arranged between the ring actuators 41.1, 41.2, 41.3 and the correspondingly designed base body 31. In the 4a and 4b A base body 31 is shown with a pin 35.1, 35.2, onto which the ring actuators 41.1, 41.2 are pushed. The ring actuators 41.1, 41.2 can be controlled for assembly in such a way that the inner diameter is increased, whereby the ring actuator 41.1, 41.2 is shrunk onto the pin 35.1, 35.2 after it has been applied and returned to its original state, the connecting layer 50 being ductile Behavior creates a flat surface and thereby an advantageous homogenization of the mechanical stresses. Alternatively, the ring actuators 411, 41.2 can be shrunk by heating or cooling the base body 31 and/or the actuator 41. The assembly of the ring actuators 41.1, 41.3 in the 4c and the 4d cylindrical 36.1 or conical recess 36.2 shown can be carried out using a corresponding procedure. In addition to a cylindrical or conical shape, the contact surface can also have any other suitable geometry.

5a shows a schematic representation of an optical assembly 30, with a base body 31, an add-on part 38 and a connecting layer 50 arranged between them, the components 31, 38, 50 being shown individually to explain the method and for the purpose of simplification for the individual components 31, 38, 50 general terms can be used, in particular for the attachment 38, which is designed, for example, as an actuator. The ones in the 5a The embodiment shown has a connecting layer 50 designed as a separate component, which is inserted between the attachment 38 and the base body 31 during assembly before joining. The connecting layer 50 can, for example, comprise pure aluminum, which is ductile in its pure form and compensates for the shape tolerances of the contact surfaces through plastic deformation. After assembly, the connecting layer 50 can be solidified in an aging step, such as by diffusion hardening, aging hardening or nitriding, at least in the area of the surface, and, depending on the thickness of the connecting layer 50, can also harden completely. As a result, the connecting layer 50 loses ductility in favor of higher strength, which results in a rigid connection of the attachment 38 to the base body 31, which is advantageous for normal operation, as a result of which the connecting layer 50 no longer plastically deforms or flows due to the actuator forces, but rather maintains its shape .

5b shows a schematic representation of a further embodiment of an optical assembly 30. The connecting layer is designed as a coating 51, which is applied to the base body 31. After joining, as in the 5a already explained, an outsourcing step for adapting the physical material properties of the connecting layer 51 to the requirements during normal operation of one in the 1 and the 2 projection exposure systems 1, 101 described. Alternatively, the coating 51 can also be formed on the base body 31 and on the component 38. This has the advantage that the aging step can also include, for example, so-called thermocompression bonding, in which the diffusion of metal atoms of the two coatings 51 is promoted by pressure and temperature, which creates a connection similar to cold welding, which can also transmit tensile forces. This expediently also requires a connection between the coating 51 and the components 31, 38, which can also transmit tensile forces. The joining temperatures required for this can be advantageously reduced by special process conditions, such as those known from direct bonding, such as joining under a vacuum environment and the activation of the joining surfaces before joining.

5c shows a schematic representation of a further embodiment of an optical assembly 30 according to the invention, the components 31, 38 again being shown as individual components. The base body 31 and the attachment 38 each have a coating 51.1, 51.2, which comprise different materials. The different materials of the two coatings 51.1, 51.2, with a suitable choice of material and an appropriate removal step, enable a firm connection that can transmit tensile forces. The ductile properties of the materials of the two coatings 51.1, 51.2, which are advantageous for compensating for shape tolerances and surface roughness of the contact surfaces and for forming a force-free connection, can therefore be used when assembling the optical assembly 30 and can be converted into a material by a subsequent aging step physical material properties required during normal operation, such as strength and dimensional stability. Such an outsourcing step can also be used for different materials and can already be used in the 5b thermocompression bonding explained, as well as alternatively euctectic joining and the so-called solid-liquid interdiffusion bonding (SLID), which is briefly explained below. Solid-liquid interdiffusion bonding is used in the production of microsystem components, in which, in addition to the mechanical encapsulation of sensor and actuator units, the electrical contacting of them must also be realized. As a result, conductive and therefore primarily metallic connections must be used. Solid-liquid interdiffusion bonding is based on a short-term liquid phase of a first, low-melting bonding partner and the subsequent isothermal solidification through diffusion and mixing with a second bonding partner. The resulting connection can also transmit tensile forces. Eutectic joining, which is possible, for example, with material pairings such as gold and indium or copper and tin or gold and tin, is based on the fact that when the two materials come into contact, the metal atoms diffuse, which forms an alloy. In eutectic systems, the melting temperature of the eutectic alloy, known as the eutectic, is lower than the melting temperature of the pure substances. In the in the 5c In the embodiment shown, the attachment 38 is coated, for example, with gold 51.1 and the base body 31 is coated with indium 51.2. Depending on the process, the coatings 51.1, 51.2 are not leveling, so that the surfaces of the coating 51.1, 51.2 correspond to the surface of the attachment 38 or the base body 31. The surface tolerances and surface roughness usually lead to a first contact at three points between the two coatings 51.1, 51.2, at which the diffusion of metal atoms between the coatings 51.1, 51.2 starts. If the components 31, 38 joined in this way are now heated above the eutectic temperature, melting occurs in the area of the eutectic newly created by the diffusion. This is displaced by slight pressure, which is caused, for example, by the weight or the expansion of the two components 31, 38 due to the temperature, and flows into the existing gaps, whereby they are filled. This increases the contact area between the two coatings 51.1, 51.2 and thus also the area in which metal atoms diffuse between the coatings 51.1, 51.2. The resulting continuous increase in the contact area ultimately leads to complete contact with a continuous contact area and a connection of the two components 31, 38 through the connecting layer 50, which almost completely contains the eutectic formed by the diffusion process. The two coatings 51.1, 51.2 are converted into the connecting layer 50 during assembly and the subsequent aging step. The eutectic has elastic behavior and high strength.

The ones in the 5a until 5c The method described and the materials used are not limited to metals and can also include plastics, such as parylene, in which case heating close to the glass transition temperature of the plastic is necessary in the aging step to connect the two components 31, 38. Furthermore, processes with materials that liquefy under the influence of temperature or show a viscous behavior and turn back into a solid when cooled are also conceivable, as is the case, for example, with a classic oven soldering process.

The 5d shows a schematic representation of a further optical assembly 30 according to the invention, the components 31, 38, 50 again being shown as separate components. The ones in the 5d illustrated embodiment has in addition to those in the 5c Coatings 51.1, 51.2 shown on the attachment 38 and the base body 31 have an additional connecting layer 50. This can have the same materials as the coatings 51.1, 51.2 or can have a material corresponding to the coatings 51.1, 51.2 to form a eutectic. For example, the coatings 51.1, 51.2 may include gold and the connecting layer 50 may include tin, which makes eutectic joining possible. In principle, the connecting layer 50 can also have two layers of different material, so that eutectic joining between coatings 51.1, 51.2, which have a different material, is also possible.

Reference symbol list

1

Projection exposure system

2

Lighting system

3

Radiation source

4

Illumination optics

5

Object field

6

Object level

7

Reticule

8th

Reticle holder

9

Reticle displacement drive

10

Projection optics

11

Image field

12

Image plane

13

wafers

14

wafer holder

15

Wafer displacement drive

16

EUV radiation

17

collector

18

Intermediate focal plane

19

Deflecting mirror

20

Facet mirror

21

facets

22

Facet mirror

23

facets

30, 30.1-30.7

Optical assembly

31

Basic body

32

optical effective surface

33

back

34.1, 34.2

recess

35.1,35.2

cylindrical, conical tenon

36.1, 36.2

cylindrical, conical recess

37

optics body

38

Attachment part

40

Unidirectional actuator, axially connected

41.1-41.3

Ring actuator cylindrical, conical inside, conical outside

42

lever

43

storage

44

Backplate

45

counter bearing

47

Frame

48

Unidirectional actuator, radially connected

49

Actuator unit

50

Connection layer

51,51.1,51.2

Coating as a connecting layer

101

Projection exposure system

102

Lighting system

107

Reticule

108

Reticle holder

110

Projection optics

113

wafers

114

wafer holder

116

DUV radiation

117

optical element

118

versions

119

Lens housing

M1-M6

Mirror

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102020210773 A1 [0004]
• DE 102008009600 A1 [0039, 0043]
• US 2006/0132747 A1 [0041]
• EP 1614008 B1 [0041]
• US 6573978 [0041]
• DE 102017220586 A1 [0046]
• US 2018/0074303 A1 [0056]

Claims (15)

Method for connecting a base body (31) of an optical element (Mx, 117) and an attachment (38) of an optical assembly (30.x), a connecting layer (50, 51,) between the attachment (38) and the base body (31). 51.1,51.2) is arranged to minimize stress increases in the area of the connecting layer (50,51,51.1,51.2), comprising the following process steps: - joining the base body (31), the connecting layer (50,51,51.1,51.2) and the add-on part (38), -Removal of at least one area of the optical assembly (30.x), which at least partially includes the connecting layer, to accommodate material in at least a partial area of the connecting layer (50,51,51.1,51.2). Procedure according to Claim 1 , characterized in that at least one physical property changes at least in a near-surface area of the connecting layer (50,51,51.1,51.2) due to the absorption of material. Procedure according to one of the Claims 1 or 2 , characterized in that the connecting layer (50,51,51.1,51.2) is formed at least in two parts before joining. Procedure according to Claim 3 , characterized in that the at least two parts of the connecting layer (51,51.1,51.2) are formed as coatings on the base body (31) and on the add-on part (38) before joining. Procedure according to one of the Claims 3 or 4 , characterized in that the two parts of the connecting layer (50,51,51.1,51.2) have different materials. Procedure according to Claim 5 , characterized in that the different materials include gold and indium or copper and tin or gold and tin. Procedure according to one of the Claims 5 or 6 , characterized in that the different materials interact with each other during storage. Method according to one of the preceding claims, characterized in that the joining takes place without force. Optical assembly (30.x) with a base body (31) of an optical element (Mx, 117) and an attachment (38), with a connecting layer (50,51,51.1) between the attachment (38) and the base body (31), 51.2) is arranged to minimize stress increases in the area of the connecting layer (50,51,51.1,51.2), characterized in that the connecting layer (50,51,51.1,51.2) is designed such that the change in the volume of the connecting layer (50 ,51,51.1,51.2) with fluctuations in the humidity surrounding the connecting layer (50,51,51.1,51.2) in the range of 0% rel. Humidity up to 60% rel. Moisture is less than 5% by volume, preferably less than 2% by volume and particularly preferably less than 0.1% by volume. Optical assembly (30.x) according to Claim 9 , characterized in that the connecting layer is designed as a separate component (50). Optical assembly (30.x) according to Claim 9 , characterized in that the connecting layer is designed as a coating (51,51.1,51.2). Optical assembly (30.x) according to Claim 11 , characterized in that the connecting layer is designed as a coating (51,51.1,51.2) arranged on the base body (31) and a coating (51,51.1,51.2) on the add-on part (38). Optical assembly (30.x) according to Claim 12 , characterized in that the two coatings (51.1,51.2) comprise different materials. Optical assembly (30.x) according to one of the Claims 11 - 13 , characterized in that the connecting layer (51,51.1,51.2) is non-positively connected to the base body (31) and/or the add-on part (38). Projection exposure system (1,101) with an optical assembly (30.x) according to one of the previous ones Claims 9 - 14 .

Images