DE102022208206A1 - Method for stabilizing an adhesive connection of an optical assembly - Google Patents

Abstract

The invention relates to a method for thermally stabilizing an adhesive connection (37) of two components (Mx, 117,33,38,34) of an optical assembly (30.1,30.2,30.3), comprising the following process steps: - Production of the adhesive connection (37) between the Components (Mx,117, 33, 38, 34), - curing the adhesive (36), - tempering the adhesive (36) to increase the degree of curing and the temperature of the glass transition region of the adhesive (36).

Description

The invention relates to a method for stabilizing an adhesive connection of an optical assembly, in particular an optical assembly for a projection exposure system for semiconductor lithography.

Such systems are used to produce the finest structures, especially on semiconductor components or other microstructured components. The functional principle of the systems mentioned is based on producing the finest structures down to the nanometer range by means of 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. The minimum dimensions of the structures created depend directly on the wavelength of the light used. Recently, 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 13.5 nm, have increasingly been used. The wavelength range described is also referred to as the EUV range.

In addition to EUV systems, the microstructured components are also manufactured with the DUV systems established on the market with a wavelength between 100nm and 400nm, in particular 193nm. Due to the introduction of the EUV range and thus the possibility of producing even smaller structures, the requirements for the optical correction of DUV systems with a wavelength of 193nm have also increased further. In addition, with each new generation of projection exposure systems, regardless of the wavelength, the throughput also increases in order to increase economic efficiency, which typically leads to greater thermal stress and thus to increasing thermally caused imaging errors. To correct the imaging errors, manipulators can be used, among other things, which change the position and orientation of the optical elements or influence the imaging properties of the optical elements, in particular mirrors, by deforming the optically active surfaces. The manipulators usually include an actuator and a sensor, which are often connected to the optical element via an adhesive. The adhesive has a glass transition region which corresponds to the temperature range in which the behavior of the adhesive changes from a purely elastic behavior to an initially at least partially plastic to a completely plastic behavior of the adhesive.

However, during the production of the corresponding optical assemblies and also during their subsequent operation in a system, temperatures in the glass transition range are regularly reached. If a temperature in the glass transition range is reached in such processes, undesirable effects can occur in the corresponding adhesive bonds.

The object of the present invention is to provide a method which eliminates the disadvantages of the prior art described above.

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

• - Herstellung der Klebstoffverbindung zwischen den Komponenten,
• - Aushärten des Klebstoffs,
• - Tempern des Klebstoffs zur Erhöhung des Aushärtegrads und der Temperatur des Glasübergangsbereichs des Klebstoffs.

A method according to the invention for thermally stabilizing an adhesive connection between two components of an optical assembly comprises the following method steps:

• - Creation of the adhesive connection between the components,
• - curing of the adhesive,
• - Tempering the adhesive to increase the degree of hardening and the temperature of the glass transition region of the adhesive.

The measure according to the invention of tempering the already hardened adhesive and the associated increase in the glass transition temperature ensures that the adhesive connection shows increased robustness against heating in the further course of the processing of the optical assembly, in particular does not begin to show mechanical drift when exposed to external forces , for example to crawl. The tempering process starts after the adhesive has hardened, in particular at room temperature, and consists of a single or multiple controlled heating of the adhesive above room temperature. The associated desired increase in the glass transition temperature of the adhesive depends on various parameters, in particular on the temperature profile over time, the maximum temperature, other environmental conditions and of course also on the type of adhesive used.

During the tempering process itself, it is to be expected that the heated adhesive assumes states in which tensions relax or, under the influence of external forces, there is a plastic deformation of the adhesive and thus a change in the mechanical parameters of the adhesive connection compared to the state before the tempering cess is coming. This could result in undesirable effects, in particular a change in the orientation of the two joined components to one another or even deformations of the components in the area of the adhesive connection after tempering. It therefore proves to be advantageous if at least one of the components is influenced during the tempering of the adhesive in such a way that the input of forces by the component into the adhesive is reduced.

For example, it is conceivable that due to the influence of gravity on one of the components during the tempering process and the associated temporary weakening of the adhesive connection, a mechanical drift of these components occurs in the direction of the effect of gravity. In this case, the input of forces into the adhesive resulting from the acting gravity could be reduced by providing the corresponding component with a holder or otherwise supporting it. The holder can be designed passively or actively to compensate for different thermal expansion coefficients.

However, the forces can also be forces that are caused by temperature changes in at least one of the components.

For example, a different thermal expansion coefficient of one of the components and the adhesive can lead to tensions arising along the joining surface and in the adhesive itself when the temperature changes, which relax during the tempering process and thus change the mechanical conditions of the joint compared to the state before the tempering process .

Such a situation can occur in particular if one of the components is an optical element and the other of the components is a solid-state actuator, for example an electrostrictive or piezoelectric actuator.

In this case, a change in temperature affects at least two different ways. Firstly, the temperature change, in a known manner, leads to different thermal expansion of the adhesive, the optical element and the actuator, which can result in undesirable stresses during the annealing process. Secondly, as the temperature changes, the control behavior of electrostrictive or piezoelectric actuators in particular also changes, so that with the applied electrical voltage remaining the same, the deflection of the actuator changes due to the temperature dependence of the electrostrictive or piezoelectric effect.

This problem can be addressed by controlling the solid-state actuator with a variable electrical voltage during the annealing process, so that the effects described above can be compensated for by a suitable electrical control of the actuator and, as a result, the entry of external forces into the adhesive bond during the annealing process is reduced.

There are various options for connecting an actuator to an optical element, for example to a base body of a mirror of a projection exposure system for semiconductor lithography. For example, in a first variant, the actuator can be connected to a mirror in a non-deflected state, i.e. without an applied electrical voltage, which deviates on its optical effective surface in the area of the actuator in this state from a so-called zero position, which it has in normal operation would accept. In this case, for example, there can be a concave partial area on the optical effective surface in the area of the actuator. The zero position of the effective surface of the optical element is then achieved by expanding the actuator by applying a default voltage in such a way that the concave area is neutralized. A local deformation of the optical effective surface around the zero position, i.e. in both concave and convex directions, can then be achieved by the voltage applied to the actuator either exceeding or falling below the default voltage. In this case, it is advantageous for the tempering process if the voltage at the start of the tempering process corresponds to the voltage in a non-deflected state of the actuator, because in this case no or only small forces are exerted by the actuator on the adhesive connection.

However, it is also possible to initially manufacture a mirror in such a way that it assumes the zero position on its optical effective surface without the action of an actuator. In this case, the actuator can then be connected to the mirror in a deflected state, i.e. under the influence of an electrical voltage. A desired deformation of the optical effective surface around the zero position can then also be achieved by varying the electrical voltage on the actuator. In contrast to the aforementioned variant, the force input of the actuator into the adhesive connection is minimal when a certain control voltage is applied to it, ie when it has already been deflected by a certain amount. In this case it is advantageous if the Voltage at the start of the annealing process corresponds to the voltage in a deflected state of the actuator, in particular in the state which corresponds to the zero position of the optical effective surface and which was applied to the actuator during the bonding of the actuator to the mirror.

In particular, a laser beam can be used for the tempering process, which is specifically aimed at the adhesive connection.

This measure can ensure that only the adhesive connection is heated during the tempering process, so that the disadvantageous thermal effects on the surrounding components described above are reduced or avoided.

• 1 schematisch im Meridionalschnitt eine Projektionsbelichtungsanlage für die EUV-Projektionslithografie,
• 2 schematisch im Meridionalschnitt eine Projektionsbelichtungsanlage für die DUV-Projektionslithografie,
• 3 eine aus dem Stand der Technik bekannte optische Baugruppe,
• 4a,b eine weitere aus dem Stand der Technik bekannte optische Baugruppe,
• 5 ein Diagramm zur Erläuterung des erfindungsgemäßen Verfahrens,
• 6 ein weiteres Diagramm zur Erläuterung des erfindungsgemäßen Verfahrens, und
• 7 ein Flussdiagramm zu einem erfindungsgemäßen Herstellungsverfahren.

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,
• 3 an optical assembly known from the prior art,
• 4a,b another optical assembly known from the prior art,
• 5 a diagram to explain the method according to the invention,
• 6 another diagram to explain the method according to the invention, and
• 7 a flowchart for a manufacturing method according to 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 (GI), i.e. with angles of incidence greater than 45° relative to the normal direction of the mirror surface, or in normal incidence (NI), i.e. with angles of incidence smaller than 45°, with the illumination radiation 16. The collector 17 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation and on the other hand 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 be exactly a mirror, dude but natively also have 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 include one or two mirrors for perpendicular incidence (NI mirror, normal incidence mirror) and/or one or two mirrors for grazing incidence (GL 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 projection optics 10 can in particular be anamorphic. In particular, it has different imaging scales βx, βy in the x and y directions. The two imaging scales βx, βy of the projection optics 10 are preferably (βx, βy) = (+/- 0.25, +/- 0.125). A positive image scale β means an image without image reversal. A negative sign for the image scale β means an image with image reversal.

The projection optics 10 thus leads to a reduction in size in the x direction, that is to say in the direction perpendicular to the scanning direction, in a ratio of 4:1.

The projection optics 10 leads to a reduction of 8:1 in the y direction, that is to say in the scanning direction.

Other image scales are also possible. Image scales of the same sign and absolutely the same in the x and y directions, for example with absolute values of 0.125 or 0.25, are also possible.

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 over the overlay of different lighting channels can be achieved.

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. When imaging the projection optics 10, which images the center of the pupil facet mirror 22 telecentrically onto the 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.

In 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 110 with the lens housing 119 differs except in the additional use of refractive optical elements 117 such as lenses, Prisms, end plates in principle not of the in 1 Structure described and will therefore not be described further.

3 shows an optical assembly 30.1 known from the prior art, as shown in one of the 1 and 2 explained projection exposure systems 1, 101 can be used. The assembly includes as components a mirror Mx, 117 and a sensor element designed as a reference mirror 33 for an interferometer, not shown in the figure. The mirror Mx, 117 comprises an optical effective surface 32 for reflecting the useful radiation of the projection exposure system 1, 101 and a side surface 40 adjoining the optical effective surface 32. The reference mirror 33 is in the 3 illustrated embodiment connected to the mirror side surface 40 by means of an adhesive connection 37 with an adhesive 36. Heating up to the glass transition region of the adhesive 36 or beyond in further process steps for the production or during operation of the optical assembly 30.1 can cause a plastic deformation of the adhesive 36, which, in conjunction with the weight force G acting on the reference mirror 33, leads to a displacement of the Reference mirror 33, as in the 3 shown by the dashed lines.

To mechanically stabilize the adhesive connection 37 for subsequent process steps, it is tempered using the method according to the invention. The adhesive 36 in the adhesive connection 37 is used, for example, by one in the 3 Directed laser beam, not shown, is heated in a controlled manner in such a way that the glass transition region of the adhesive 36, i.e. the temperature range in which the adhesive begins to show mechanical glass-like properties, is increased. The tempering is expediently carried out in such a way that the glass transition region of the adhesive 36 after the tempering step is above the temperatures occurring in the further process steps, such as above 40 ° Celsius, or at least the lower limit of the glass transition region is exceeded by only a few Kelvin.

Heating the adhesive 36 with a laser has the advantage that, due to the associated local heating possibility, less heat is introduced into the mirror Mx, 117 and the reference mirror 33, which results in a change in the position and orientation of the reference mirror 33 relative to the mirror Mx, 117 can be kept as low as possible or even completely avoided through thermal expansion of the components involved.

To avoid changing the position and/or alignment of the reference mirror 33 relative to the mirror Mx, 117 due to plastic deformation of the adhesive 36 during the aforementioned tempering step, the reference mirror 33 is held by a holder 39 in the predetermined target position relative to the mirror Mx, 117, whereby in particular the effect of weight can be compensated. In the event of heating of the entire optical assembly, it may be necessary to adjust the holder 39 to maintain the predetermined target position of the reference mirror 33 during tempering in order to compensate for different thermal expansions of the reference mirror 33, the mirror Mx, 117 and the adhesive 36.

4a shows an optical assembly 30.2 known from the prior art, as shown in one of the 1 and 2 explained projection exposure systems can be used. This includes as components a mirror Mx, 117, actuators 38 and a back plate 34. The mirror Mx, 117 includes an optical effective surface 32 and a mirror back 31 opposite the optical effective surface 32. The actuators 38 are covered with adhesive 36 on one side Mirror back 31 and on the other side with a contact surface 35 of the back plate 34 directed towards the mirror back 31 of the mirror Mx, 117. The actuators 38 are supported on the back plate 34 and deform the mirror Mx, 117 by the deflection of the actuators 38. The in the 4a In the embodiment shown, actuators 38 designed as piezoelectric actuators can be subjected to a preload provided by a control (not shown) when gluing, so that the actuators 38 are glued to the back of the mirror 31 in an already partially deflected state. In this case, the mirror Mx,117 is in its zero position when bonded to the already partially deflected actuator 38. In the zero position, the optical effective surface 32 of the mirror Mx, 117 is designed such that it corresponds to the target optical effective area predetermined by the optical design. From this zero position, the mirror Mx, 117 can now be in operation 1 and 2 explained projection exposure system 1, 101 to compensate for imaging errors can be deflected in two directions in that the electrical bias voltage on the actuator 38 is either undershot or exceeded. In this case, no stresses are introduced into the adhesive 36 by the actuator 38 when the optical effective surface 32 is in the zero position.

4b shows a further embodiment of an optical assembly 30.3 known from the prior art, as also shown in an in the 1 and 2 explained projection exposure systems can be used. In contrast to that in the 4a explained optical assembly 30.2 includes the in the 4b explained optical assembly 30.3 no back plate 34. The actuators 38, which are also designed as piezoelectric actuators 38, are connected to the mirror back 31 opposite the optical active surface 32 with an adhesive 36 in the form of an adhesive connection 37. The actuators 38 use the effect of the piezoelectric material that, when deflected in a first preferred direction, it contracts or expands perpendicular to it. The force caused by this is transmitted to the back of the mirror 31 via the adhesive connection 37, whereby the mirror Mx, 117 and thus the optical effective surface 32 are deformed. As per the 4a already explained, the actuators 38 can be glued to the back of the mirror 31 under application of a preload provided by a control (not shown), so that analogous options for adjusting the deformation of the optical effective surface 32 arise, as already explained 4a explained.

As an alternative to applying a preload to the actuators 38 when bonding to the mirror back 31, the deformation of the optical effective surface 32 caused by the deflection of the actuators 38 can be maintained during the production of the optical effective surface 32.

In other words, the mirror Mx, 117 is manufactured in such a way that in the absence of actuators or when the actuators are not activated, its optical effective surface 32 deviates from the zero position in various areas. The zero position of the optical effective surface 32 is then set during operation of the corresponding system by controlling the actuators 38 accordingly. In this case, a mechanical tension acts on the adhesive connection 37 even during the zero position of the optical effective surface. Such mechanical tension would at least partially relax during a tempering process. This would lead to the stress conditions before the annealing process being different from those after the annealing process.

5 describes the tempering process according to the invention, with which the adhesive connection 37 of an optical assembly can be stabilized. The glass transition region of the adhesive 36 is increased by a tempering process following the bonding in such a way that the glass transition region begins higher than the process temperatures of the subsequent processes or the relaxation of the mechanical stress in the adhesive 36 drops to an acceptable level in the subsequent processes.

In a first method step 41, a component 38 is connected to an optical element Mx, 117 by an adhesive 36.

In a second process step 42, the adhesive 36 is cured.

In a third method step 43, the adhesive 36 is tempered to increase the degree of hardening and the glass transition region of the adhesive 36.

As already mentioned, the annealing process brings with it the problem that even in those cases in which it is started in a state in which no external force is exerted on the adhesive connections 37 by the actuator 38, undesirable forces arise as the temperature increases.

One of the underlying mechanisms should be based on the 6 be explained. 6 shows a diagram in which the deflection s of an actuator 38 is shown schematically via an applied voltage U at different temperatures. A clear dependence of the relationship between the applied voltage U and the deflection s on the temperature T can be seen from the individual curves, which were recorded at different temperatures T1, T2, T3, T4, T5. T1 corresponds to the lowest ambient temperature and T5 to the highest prevailing ambient temperature, whereby the representation is standardized to the conditions at temperature T1.

Easily visible in the 6 On the one hand, the dependence of the expansion of the actuator s on the voltage U decreases with increasing temperature. The effect of the thermal expansion of the actuator 38 as the temperature increases is also clearly visible.

According to the invention, during the annealing process, the voltage applied to the actuator 38 is determined depending on the prevailing temperature in accordance with the exemplary illustration 7 adjusted. The selected relationship between temperature T and voltage U ensures that stresses occurring in the adhesive connection 37 are minimized due to thermal effects, i.e. on the one hand due to the sensitivity of the actuator to electrical voltage changes that decreases with increasing temperature and on the other hand the thermal expansion of the actuator itself, so that as little as possible or no relaxation processes of the adhesive connection 37 occur during the tempering process.

A determination of the voltage curve versus temperature required for the desired effect can be carried out, for example, experimentally or through simulations, in particular using finite element methods.

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

30.1 -30.3

Optical assembly

31

Mirror back

32

optical effective surface

33

Reference mirror

34

Backplate

35

Contact surface back plate

36

adhesive

37

Adhesive connection

38

actuator

39

bracket

40

side surface

41

Procedural step

42

Procedural step

43

Procedural step

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

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Cited patent literature

• DE 102008009600 A1 [0032, 0036]
• US 20060132747 A1 [0034]
• EP 1614008 B1 [0034]
• US 6573978 [0034]
• DE 102017220586 A1 [0039]
• US 20180074303 A1 [0053]

Claims (10)

Method for thermally stabilizing an adhesive connection (37) of two components (Mx, 117,33,38,34) of an optical assembly (30.1,30.2,30.3), comprising the following method steps: - Production of the adhesive connection (37) between the components (Mx, 117, 33, 38, 34), - curing the adhesive (36), - Tempering the adhesive (36) to increase the degree of hardening and the temperature of the glass transition region of the adhesive (36). Procedure according to Claim 1 characterized in that during the tempering of the adhesive (36), at least one of the components (Mx, 117,33,38,34) is influenced in such a way that the input of forces through the component (Mx, 117,33,38,34) into the adhesive (36) is reduced. Procedure according to Claim 2 , characterized in that the forces are forces which are caused by temperature changes in the component (Mx, 117,33,38,34). Method according to one of the preceding claims, characterized in that one of the components is an optical element (Mx, 117). Method according to one of the preceding claims, characterized in that one of the components is a solid-state actuator (38). Procedure according to Claim 5 characterized in that the solid-state actuator (38) is controlled with a variable electrical voltage during the annealing process. Procedure according to Claim 6 , characterized in that the voltage at the start of the annealing process corresponds to the voltage in a non-deflected state of the actuator (38). Procedure according to Claim 6 , characterized in that the voltage at the start of the annealing process corresponds to the voltage in a deflected state of the actuator (38). Method according to one of the preceding claims, characterized in that a laser beam is used for the tempering process, which is specifically aimed at the adhesive connection (37). Method according to one of the preceding claims, characterized in that the method is used for a component of a projection exposure system for semiconductor lithography (1,101).

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