DE102022211637A1 - Thermally deformable mirror element and its use, thermal deformation system and lithography system - Google Patents

Abstract

A thermally deformable mirror element (80) is disclosed, comprising a mirror body (81) with a deformation layer (86) and a base body (84) and a reflection surface (82) arranged on a surface of the deformation layer (86), the deformation layer (86) is formed from a deformation material with an expansion coefficient which has a value not equal to zero, and wherein the base body (84) is designed to retain its shape when the deformation layer (86) is heated, the mirror element (80) and a heating device ( 21) for heating at least one region (22) of the deformation layer (86) comprising a thermal deformation system (20) and a lithography system (1) comprising the mirror element (80) and/or the thermal deformation system (20) and the use of the mirror element (80) in a projection system (11).

Description

The present invention relates to a thermally deformable mirror element and its use in a projection system, as well as a thermal deformation system and a lithography system, each of which comprises the mirror element.

The lithographic production of integrated circuits with particularly small structures requires the use of very short-wave, deep ultraviolet or extreme ultraviolet radiation (DUV or EUV radiation) with a wavelength between 5 and 100 nm (EUV radiation) or between 100 nm and 300 nm (DUV radiation) and the provision of appropriately designed lithography systems. In order to achieve a high imaging quality here, the beam shaping effected in a beam path of the radiation of such a lithography system, in particular by mirrors, must be able to be set particularly precisely. In this case, it may be necessary to set such a beam shaping that cannot be achieved by positioning and aligning a mirror alone. For this purpose, such a mirror can be designed to be thermally deformable. In this way, the geometric dimensions of the mirror and also its shape can be changed by heating, thus changing its optical properties and adjusting its effect on beam shaping. Such a thermally deformable mirror is from U.S. 10,031,423 B2 known.

However, the imaging quality in a lithography system can only be determined ex situ outside of the actual exposure process of a wafer to be exposed, so that for a defined change in the optical properties of a mirror in the beam path and thus for setting a defined beam shaping, the mirror used and the mirror used can be modeled as precisely as possible changing its optical properties is required.

In order to provide such a model, a correspondingly extensive knowledge of the mirror and the possible changes in the optical properties is required. Accordingly, a model of a thermally deformable mirror requires knowledge in particular of the type and extent of the thermal deformation caused by a respective heating. Since a large number of effects, some of which are functionally connected to one another, have to be taken into account in order to determine the thermal deformation, a large number of relevant parameters must be taken into account in order to create a suitable model of a thermal deformation. In particular, this makes the setting of a defined beam shaping of a thermally deformable mirror element particularly complex in the case of ex-situ control.

Against the background of the problems mentioned above, it is therefore an object of the present invention to provide an improved thermally deformable mirror element which, in particular, enables improved adjustability of the beam shaping effected by the mirror element, above all in the case of ex-situ control.

The solution according to the invention lies in the features of the independent claims. Advantageous developments are the subject of the dependent claims.

According to the invention, a thermally deformable mirror element is disclosed, comprising a mirror body with a deformation layer and a base body as well as a reflection surface arranged on a surface of the deformation layer, the deformation layer being formed from a deformation material with a coefficient of expansion that is not equal to zero, and wherein the base body is designed to retain its shape when the deformation layer is heated.

The mirror element can, for example, be a component of an EUV and/or a DUV lithography system, in particular a projection system of such a lithography system.

• Unter „thermischer Deformation“ ist die Änderung der geometrischen Abmessungen eines Körpers bei seiner Erwärmung zu verstehen. Der Zusammenhang zwischen der Änderung der geometrischen Abmessung und der Temperaturänderung wird durch den Ausdehnungskoeffizienten beschrieben.

Some of the terms used in connection with the invention are first explained below:

• "Thermal deformation" means the change in the geometric dimensions of a body when it is heated. The relationship between the change in geometric dimensions and the change in temperature is described by the coefficient of expansion.

A “expansion coefficient” is usually a temperature-dependent parameter, the value of which describes the behavior of a substance with regard to changes in its dimensions when the temperature changes. It is a substance-specific material constant. The expansion coefficient of the deformation material should have a value not equal to zero. In particular, a non-zero value of the coefficient of expansion can be present for each temperature within a temperature range that is included in an operating temperature range provided for the mirror element during proper operation or corresponds to this provided operating temperature range. Is the Expansion coefficient "zero-crossing-free", it also does not assume any values with different signs or a value of zero.

A “normal direction” should be understood to mean a direction along a surface normal of the reflection surface. Similarly, a "normal extension" describes an extension in the normal direction. The “lateral extent” thus designates an areal extent in a plane perpendicular to a normal extent.

The invention relates to an advantageous embodiment of a thermally deformable mirror element that has a deformation layer. The shape of the reflection surface arranged on a surface of the deformation layer can be changed by thermal deformation of the deformation layer. In this way, the beam shaping effected by the mirror element can be adjusted by heating the deformation layer.

Since the base body of the mirror body is designed to retain its shape when the deformation layer heats up, the thermal deformation can be limited to the deformation layer, which simplifies the modeling of the thermal deformation of the mirror element and the resulting setting of the beam shaping. For example, the normal extent of the deformation layer is less than half, preferably less than a quarter, more preferably less than an eighth of the normal extent of the mirror element. In particular, the modeling is not made more difficult by the local inhomogeneities that are typically always present in the materials used for the base body.

The normal extent of the deformation layer can be selected such that a temperature difference within the deformation layer can be neglected, or that a predetermined maximum temperature difference between the reflection surface and a side of the deformation layer opposite the reflection surface is not exceeded during intended operation of the mirror element. In this way it is possible to model the mirror element and its thermal deformation with a two-dimensional temperature field.

The scope of the parameters required for modeling the thermal deformation of the mirror element according to the invention for setting the beam shaping can therefore be significantly reduced, which significantly simplifies the modeling of the thermal deformation of the mirror element and the calculation effort required for this can be significantly reduced. This enables improved adjustability of a defined beam shaping of the reflected radiation, in particular the manipulation of the shape of the wave front of the reflected radiation.

For example, the normal extent of the deformation layer is in a range from 100 μm to 10 mm. The normal extent of the deformation layer can be in a range from 100 μm to 2 mm, for example in the case of forming the deformation layer as a coating. For example, if the deformation layer is formed as a component attached to the base body by means of joining, the normal extent of the deformation layer can also be in a range from 1 mm to 10 mm, preferably from 1 mm to 5 mm, particularly preferably from 2 mm to 4 mm . In an exemplary arrangement of a cooling layer in the base body, the normal extent of the deformation layer can also be in a range from 1 mm to 5 mm, preferably in a range from 1 mm to 3 mm.

The reflective surface of the mirror element is designed to reflect radiation and thereby shape the beam. The shape of the reflected radiation can be influenced by the shape of the reflection surface. The reflection surface is set up, for example, to reflect radiation with a wavelength between 5 nm and 100 nm, preferably a wavelength of 13.5 nm, and/or between 100 nm and 300 nm, preferably a wavelength of 193 nm. Radiation with a wavelength between 5 nm and 100 nm is EUV radiation, radiation with a wavelength between 100 nm and 300 nm is DUV radiation. The reflection surface can be formed from one or more highly reflective coatings, for example in the form of multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The deformation layer is preferably formed from a deformation material with a zero-crossing-free coefficient of expansion. In this case, the expansion coefficient of the deformation material does not assume any values with different signs or a value of zero. Since states in which an opposite effect occurs or no effect occurs can thus remain unconsidered in the modeling of the thermal deformation of the mirror element, the adjustability of the beam shaping can be further simplified.

The base body maintains its shape when the deformation layer is heated. This can be achieved by thermally decoupling the base body from the deformation layer, so that the base body retains its temperature despite heating of the deformation layer. This can also be achieved by forming the base body from a material that is subject to negligible thermal expansion under the influence of the heat transmitted by the deformation layer, in particular in at least one intended operating situation of the mirror element. A combination of these two measures is also possible. A configuration for interaction with further means not belonging to the base body is also conceivable.

In one embodiment, the base body is formed from a base material whose temperature-dependent coefficient of expansion exhibits a zero crossing at a zero crossing temperature. In the vicinity of the zero crossing, there is no or only negligible thermal expansion. An exemplary base material is an ultra-low thermal expansion material ("ultra-low-expansion-material"), for example a material from the titanium-silicate glasses family.

Such a configuration of the base body makes it possible for its shape not to change or at least not to change substantially when the mirror element is operated in the range of the zero crossing temperature when the deformation layer heats up, even if the base body heats up as a result, for example in comparison with a simultaneous , in particular absolute, change in shape of the deformation layer. In this way, the shape of the base body can be maintained when the deformation layer is heated, without having to resort to further means.

A further, additional or alternative possibility of designing the base body to maintain its shape when the deformation layer is heated lies in thermal decoupling of the base body from the deformation layer. For this purpose, the base body can be provided with a cooling device for cooling the base body.

To cool the base body, such a cooling device can be set up to interact with a cooling device. For example, the cooling device is encompassed by the mirror element or the thermal deformation system. The interaction with a cooling device should be understood to mean that a cooling device, for example arranged outside of the mirror body, can be operatively connected to the cooling device for reducing the temperature of the base body. The cooling device is designed, for example, to interact with a fluid cooling system. The cooling device can be structurally integrated into the base body. For example, the cooling device is designed in the form of cooling channels for conducting a cooling medium provided by the cooling device.

According to one embodiment, the base body comprises a cooling layer adjoining the deformation layer with a plurality of cooling channels arranged next to one another for conducting a cooling medium. For example, the cooling channels are set up to conduct a liquid cooling medium of a fluid cooling system. The cooling medium can be provided by the cooling device.

If the deformation layer is heated, heating of the base body can be counteracted using the cooling device. In this way it can be achieved that heating is limited to the deformation layer. A thermal deformation of the mirror body is then limited to the deformation layer, and a thermally induced expansion of the base body, beyond the cooling device, can be effectively prevented, so that the base body can maintain its shape. The cooling device can thus act as a heat barrier for the base body. This is to be understood in particular as meaning that a temperature equalization between the heated deformation layer and the base body can be prevented or at least slowed down in such a way that the base body heats up to a negligible extent during operation of the mirror element. For example, the heating of the base body is less than the heating of the deformation layer by a factor of at least 5, preferably by a factor of at least 10, more preferably by a factor of at least 50.

In this case, the cooling layer can be arranged adjacent to the deformation layer. Correspondingly, the cooling layer is then arranged in a region of the base body adjoining the deformation layer.

In this way, heating of the base body can be counteracted particularly effectively. In addition, a particularly uniform temperature distribution over the base body can be achieved when the deformation layer is heated. In addition, such a configuration enables a particularly simple production of a mirror element with a mirror body assembled from individual layers.

Alternatively or additionally, the cooling layer can also be encompassed by the deformation layer. The cooling layer is arranged, for example, in a region of the deformation layer adjoining the base body. It is also conceivable that a first part of the cooling layer is surrounded by the base body and a second part of the cooling layer is surrounded by the deformation layer.

In one embodiment, the deformation layer has a plurality of subregions which are arranged areally next to one another and are thermally insulated from one another.

This is to be understood as meaning that the deformation layer is subdivided into a number of sub-areas in its lateral extent, with the heat conduction between the sub-areas being significantly reduced, for example by physically separating the sub-areas. Correspondingly, the deformation layer can have border areas arranged between sub-areas, the deformation material being encompassed only by the sub-areas but not by the border areas. For example, the boundary areas are designed as gaps, preferably with a thickness of less than 1 mm, more preferably less than 100 μm, particularly preferably less than 10 μm, so that the partial areas are spaced apart from one another by the amount of this thickness.

If a heating device is used, a temperature change can only be brought about in individual partial areas of the deformation layer and thus a change in the geometric dimensions in a specific partial area. The temperature change, and thus also the thermal deformation, can be limited to the sub-area or areas under consideration. Since only individual partial areas can be thermally deformed, orthotropic heat conduction can be achieved within the deformation layer. Furthermore, the beam shaping can be adjusted, for example, by bringing the reflection surface into a non-planar or curved shape. It is also possible in this way to arrange surface areas of the reflection surface in several parallel planes along the normal direction by thermal deformation of different partial areas.

The deformation layer can be applied to the base body by coating. However, it is also conceivable that the deformation layer is attached to the base body by means of joining. This is to be understood as meaning that the deformation layer and the base body are permanently connected to one another, for example using a joining material.

Exemplary joining methods are welding—especially laser welding, electron beam welding and friction welding—soldering with—especially low-melting—metallic solders or glass solders, gluing, reactive joining, direct joining, silicate joining or hydroxide joining. Another possible joining method is Klettwelding, in which a large number of nanowires are applied to the surfaces to be connected and the surfaces are then pressed together.

In the case of direct joining, a joining method without joining material can be used. An influence on the thermal deformation by an additional joining material can thus be avoided. However, it is also conceivable that, especially in the case of reactive joining, a joining material is used which has a low thermal conductivity compared to the deformation material, so that the joining layer represents a thermal barrier between the deformation layer and the base body, for example as a further thermal barrier in addition to a cooling layer of the body. The joining material can also be chosen such that the coefficient of expansion of the joining material essentially corresponds to that of the deformation material, for example for at least those temperatures which the deformation layer has during proper operation of the mirror element. A thermal deformation of the mirror element can be supported in this way. However, it is also conceivable that the joining material has an expansion coefficient that is lower than that of the deformation material.

Joining represents a particularly simple method for joining the deformation layer to the base body, in which the properties of the joining material can be used to advantage.

According to one embodiment, the value of the expansion coefficient of the deformation material changes with a temperature change within a temperature range of 20° C. to 80° C., preferably within a temperature range of 20° C. to 60° C., more preferably within a temperature range of 20° C. to 40 ° C, in particular within a temperature range from 20 ° C to 30 ° C, of more than 1 K, preferably more than 4 K, more preferably more than 7 K by less than 5% / K, preferably by less than 3 %/K, more preferably by less than 1.5%/K, in particular by less than 1%/K. For example, the deformation material is SiO ₂ -based and has an expansion coefficient whose value changes by less than 1%/K in the event of a temperature change of more than 7 K in a temperature range of 20°C to 30°C. For example, it is this Deformation material around quartz glass (“fused silica”). The deformation material can also be platinum, for example, which has an expansion coefficient whose value changes by 0.03%/K with a temperature change of more than 7 K in a temperature range of 20°C to 30°C.

For example, the coefficient of expansion of the deformation material is at most 20*10 ^-6 K ^-1 , preferably at most 10*10 ^-6 K ^-1 .

With such a small variation in the coefficient of expansion, the coefficient of expansion can be assumed to be a constant, temperature-independent value. This makes it possible to further simplify the modeling of the thermal deformation of the mirror element when it is heated and thus improve the controllability of the mirror element for setting the beam shaping.

The deformation material can be a ceramic or a metallic deformation material and/or an amorphous or a crystalline deformation material. The deformation material can have additional deformation options and, for example, be remanently polarizable, for example piezoelectric, and/or be remanently magnetizable. If a suitable deformation material is selected, thermal deformation of the deformation material can thus be combined with one or more of these additional deformation options. In this way, the thermal deformation can be supported using suitable physical effects.

Exemplary deformation ceramic materials are silicate ceramics, oxide ceramics (e.g. barium titanate, lithium niobate, lithium tantalate, silicon dioxide, aluminum oxide) and non-oxide ceramics (e.g. scandium nitride, silicon carbide, technical diamond), lead-containing ceramics (e.g. lead zirconate-lead titanate, PZT). Exemplary metallic deformation materials are chromium, gold, silver, platinum, palladium, aluminum and rhodium. PZT, barium titanate, scandium nitride, lithium niobate and lithium tantalate in particular have piezoelectric properties. An exemplary amorphous deformation material is glass, in particular quartz glass.

According to the invention, a thermal deformation system is also disclosed, comprising a mirror element according to the invention and a heating device for heating at least one area of the deformation layer.

The heating device is, for example, an infrared heater that heats at least one area of the deformation layer by radiation. Additionally or alternatively, the heating device can also be embodied as an electrical heater, with its heating elements being arranged in the mirror element, for example inside the mirror body, such that at least one region of the deformation layer can be heated. The heating elements of an electrical heater can be arranged in the deformation layer, for example adjacent to the reflection layer, the cooling layer or the base body. The heating elements can have a lateral extent along the reflection surface and can be arranged, for example, parallel to the reflection surface or with an angular offset. They can be arranged directly adjacent to one another. The heating elements can be designed in the form of a plurality of heating layers arranged one above the other, for example at least partially overlapping, the heating layers being electrically conductive and having different electrical resistances. It is also possible that the heating is achieved by inducing eddy currents.

In particular, it is conceivable that several areas of the deformation layer can be uniformly heated independently of one another by the heating device. The heatable areas can be areas of the deformation layer that are spaced apart from one another in the lateral direction. The heating device can be set up to uniformly heat a plurality of areas that are spaced apart from one another, for example, in particular independently of one another, with the heated areas having essentially the same temperature, for example. The sum of the areas of the areas can be, for example, more than one third, preferably more than one half, more preferably more than two thirds of the lateral extent of the reflection surface. The heatable areas can also extend, at least partially, beyond the reflection surface. For example, the lateral extent of at least one heatable area extends beyond the edge of the reflection area. The areas can be distributed, for example symmetrically, over the entire lateral extension of the mirror element. The heatable areas can be arranged point-symmetrically.

The heating of an area of the deformation layer causes a change in the geometric dimensions of this area of the deformation layer. The amount of change in the geometric dimensions, and thus also a dependent change in the beam shaping caused by the mirror element, can be calculated using the temperature change that has taken place can be determined. There are several ways to determine the temperature change. For example, the thermal deformation system can include appropriate sensors. These can be arranged, for example, in or on the mirror element or else outside of the mirror element.

Furthermore, according to the invention, a lithography system is disclosed, comprising a mirror element according to the invention and/or comprising a thermal deformation system according to the invention.

The lithography system can be a DUV lithography system or also an EUV lithography system. With the aid of a projection system, an object field arranged in an object plane can be imaged in an image plane via a plurality of optical elements. For example, a mask (also called a reticle) arranged in an object plane can be imaged onto a light-sensitive layer of a wafer arranged in the image plane.

A projection system is to be understood in particular as a system which comprises a plurality of optical elements which are arranged one after the other in a beam path in order to shape radiation entering the projection system. The optical elements of the projection system can, in particular all, be designed as mirrors. This is particularly helpful if the radiation source emits EUV radiation, since EUV radiation is generally subject to high transmission losses. The transmission losses are avoided if the radiation is only reflected and not transmitted. The mirrors can be set up for a grazing incidence of the beam path. It goes without saying that the projection system can in particular also include a plurality of mirror elements and/or thermal deformation systems according to the invention.

According to the invention, a use of a mirror element according to the invention in a projection system, in particular a projection system of a lithography system, is also disclosed.

The embodiments and configurations described above are to be understood as exemplary only and are not intended to limit the present invention in any way.

• 1 eine schematische Darstellung eines Ausführungsbeispiels eines Lithographiesystems;
• 2a eine schematische Darstellung eines Ausführungsbeispiels eines thermischen Deformationssystems in Querschnittsansicht;
• 2b eine schematische Darstellung eines weiteren Ausführungsbeispiels eines thermischen Deformationssystems in Querschnittsansicht;
• 3 eine schematische Darstellung der beispielhaften thermischen Deformationssysteme der 2a und 2b in Draufsicht;
• 4 eine schematische Darstellung eines Ausführungsbeispiels eines thermisch deformierbaren Spiegelelements in Querschnittsansicht; und
• 5 eine schematische Darstellung eines Ausführungsbeispiels eines thermisch deformierbaren Spiegelelements in thermisch deformiertem Zustand in Querschnittsansicht.

The invention is explained in more detail below by way of example with reference to the attached drawings using advantageous embodiments. Show it:

• 1 a schematic representation of an embodiment of a lithography system;
• 2a a schematic representation of an embodiment of a thermal deformation system in cross-sectional view;
• 2 B a schematic representation of a further embodiment of a thermal deformation system in cross-section;
• 3 a schematic representation of the exemplary thermal deformation systems of FIG 2a and 2 B in top view;
• 4 a schematic representation of an embodiment of a thermally deformable mirror element in cross-sectional view; and
• 5 a schematic representation of an embodiment of a thermally deformable mirror element in a thermally deformed state in cross-sectional view.

In 1 an EUV lithography system 1 is shown schematically as an exemplary embodiment of a lithography system.

The EUV lithography system 1 comprises an illumination system 10 and a projection system 11. An object field 13 in an object plane 12 is illuminated with the aid of the illumination system 10.

The illumination system 10 includes an illumination radiation source 14 which emits electromagnetic radiation in the EUV range, ie in particular with a wavelength between 5 nm and 100 nm. The illumination radiation emanating from the illumination radiation source 14 is initially bundled by a collector 15 into an intermediate focal plane 16 .

The illumination system 10 includes a deflection mirror 17 with which the illumination radiation emitted by the illumination radiation source 14 is deflected onto a first facet mirror 18 . A second facet mirror 19 is arranged downstream of the first facet mirror 18 . The first facet mirror and the second facet mirror 19 each comprise a multiplicity of micromirrors that can be pivoted individually about two axes running perpendicular to one another. The individual facets of the first facet mirror 18 are imaged in the object field 13 with the aid of the second facet mirror 19 .

With the aid of the projection system 11, the object field 13 is imaged in an image plane 9 via a plurality of mirrors 8, 8'. The mirrors 8 each include a thermal deformation system tem 20. A mask (also called a reticle) is arranged in the object plane 12 and is imaged onto a light-sensitive layer of a wafer arranged in the image plane 9 . The various mirrors of the EUV lithography system 1, on which the illumination radiation is reflected, are in the form of EUV mirrors. The EUV mirrors are provided with highly reflective coatings, for example in the form of multilayer coatings, in particular with alternating layers of molybdenum and silicon.

An exemplary thermal deformation system 20, such as that also included by the mirrors 8, is shown in 2a shown schematically in cross section. The thermal deformation system 20 includes a thermally deformable mirror element 80 with a mirror body 81, which includes a base body 84 and a deformation layer 86, on the surface of which a reflection surface 82 is arranged.

The thermal deformation system 20 also includes a heating device 21. In the exemplary embodiment presented, the heating device 21 is embodied as a plurality of infrared heaters 211, 212, which are set up by irradiating the reflective surface 82 to a region 22 of the deformation layer 86 that is adjacent to the reflective surface 82 heat.

A schematic representation of a further exemplary embodiment of a thermal deformation system 20 is shown in 2 B shown in cross-sectional view. In this exemplary embodiment, the heating device 21 is designed as an electric heater with heating elements 213, 214 which are arranged within the mirror body 81 parallel to the reflection surface 82 and at a distance from it, next to one another and directly adjacent to one another. A region 22 of the deformation layer adjoining the respective heating element 213, 214 can be heated by means of the heating elements 213, 214. example shows 2 B two heating elements 213 that are not in operation and one heating element 214 that is in operation. Correspondingly, the region 22 heated in this way by the heating device 21 comprises a region of the deformation layer 86 adjoining the heating element 214.

In the embodiments of 2a and 2 B correspond to the top views of the reflection surface 82 of the mirror element 80 of the respective thermal deformation systems 20. Therefore 3 as a schematic representation of the respective mirror element 80 in plan view of both the thermal deformation system 20 of 2a as well as the thermal deformation system 20 of 2 B to understand. What can be seen in particular is a planar, spaced-apart, point-symmetrical arrangement of regions 22 of deformation layer 86 that have been heated by the respective heating device and are located in the normal direction (perpendicular to the image plane) below reflection surface 82. Accordingly, thermal deformation systems 20 can produce a plurality of spatially separate Areas 22 of the mirror body 81 are heated independently by the respective heating device 21 evenly.

In 4 An exemplary embodiment of a thermally deformable mirror element 80 is shown in cross-sectional view. The mirror element 80 comprises a mirror body 81, on the surface of which a reflection surface 82 is arranged. The reflection surface 82 is designed to reflect radiation with a wavelength between 5 nm and 100 nm. Accordingly, the mirror element 80 can be used for reflecting EUV radiation and can be a corresponding mirror 8 of the EUV lithography system 1 as a component. Alternatively or additionally, the reflection surface 82 can also be designed to reflect radiation with a wavelength between 100 nm and 300 nm. In this case, the mirror element can be used for reflecting DUV radiation and can be a corresponding mirror 8 of a DUV lithography system as a component.

The mirror body 81 includes a base body 84, a deformation layer 86 on which the reflection surface 82 is arranged. The base body 84 includes a cooling layer 90. If the mirror element 80 is part of a thermal deformation system 20 with an electrical heating device 21, as in FIG 2 B shown, the deformation layer 86 can comprise the electrical heating elements 213, 214, for example directly adjacent to the cooling layer 90 or to the reflection surface 82.

The deformation layer 86 is formed of PZT as a deformation material having a non-zero coefficient of expansion and being zero-crossing-free. The deformation layer 86 has a plurality of partial regions 88 which are arranged areally in a direction parallel to the reflection surface 82 and are physically separate from one another. The heat conduction between the partial areas 88 that are thermally insulated in this way is considerably reduced. This makes it possible to bring about a change in the geometric dimensions as a result of thermal deformation only in individual partial areas 88 of the deformation layer 86 . By being able to change the geometric dimensions of only individual partial areas, orthotropic heat conduction within the deformation layer 86 can be achieved. Furthermore, the beam shaping effected by the mirror element 80 can be adjusted, for example, such that the reflection surface 82 is shifted both along its surface normal and also brought into a non-planar shape.

In the example of 4 corresponds to the normal extension of the deformation layer 86 100 pm. In this way, when using PZT as the deformation material, a temperature difference of the deformation layer 86 in the normal direction can be neglected when modeling the mirror element 80 and its thermal deformation, and the thermal deformation of the heated area of the deformation layer 86 can be considered with sufficient accuracy without taking into account a temperature difference must be in the normal direction. The temperature of the deformation layer 86 can thus be described using a two-dimensional temperature field when modeling the mirror element 80 and its thermal deformation.

The base body 84 includes a cooling layer 90 which extends through the entire mirror body 81 and is adjacent to the deformation layer 86 .

The cooling layer 90 comprises a plurality of cooling channels 92 arranged next to one another in a plane parallel to the reflection surface 82 and web regions 91 lying between the cooling channels 92. The cooling channels 92 are set up to interact with a cooling device and to conduct a liquid cooling medium provided by a fluid cooling system. In this way, the temperature of the regions of the mirror body 81 adjoining the cooling layer 90 can be reduced. If the deformation layer 86 is heated, the cooling layer 90 can act as a thermal barrier between the heated deformation layer 86 and the base body 84, and can counteract a temperature equalization between the heated deformation layer 86 and the base body 84, so that the base body 84 can react when the deformation layer heats up 86 can keep its shape.

In addition, the base body 84 can be formed from ultra-low expansion glass as the base material, which has a zero crossing at a zero crossing temperature. As a result, the base body 84 can still retain its shape even if the base body 84 is heated, for example unplanned. The web areas 91 can then also be formed from the base material. However, it is also conceivable for the web areas to be formed from a material that differs from the base material, which material exhibits, for example, particularly low friction when conducting the cooling medium and which, for this purpose, provides, for example, a particularly smooth inner surface of the cooling channels 92 .

5 shows the mirror element 80 of FIG 4 in a thermally deformed state. The partial area 88' has been heated by a heating device, so that the partial area 88' has been heated and the deformation material of the partial area 88' has expanded. In the example shown, the cooling layer 90 interacts with a fluid cooling system, with the cooling channels 92 conducting a cooling medium. Thus, the cooling layer 90 acts as a heat barrier between the heated portion 88 ′ of the deformation layer 86 and the base body 84 , and the heating is restricted to the portion 88 ′ of the deformation layer 86 . A thermal deformation of the base body 84 can thus be counteracted, which can thus maintain its shape. The formation of the base body 84 with a cooling layer 90 thus contributes to maintaining the shape of the base body 84 .

In the case of the mirror element 80, the deformation layer 86 is attached to the base body 84, so that the changes in the geometric dimensions result in the direction of the arrows shown. In particular, the reflection surface 82 on the surface of the partial area 88' along the surface normal of the reflection surface 82, in 5 up, shifted.

Due to the fact that an expansion also takes place parallel to the reflection surface 82, and the non-heated sub-areas 88 are thus compressed, the reflection surface 82 is additionally curved, which in 5 is indicated in the representation of the reflection surface 82 on the lateral flanks of the partial area 88`. The change in the shape of the reflection surface 82 brought about by the thermal deformation therefore corresponds to hillock formation.

In this way, the shape of the reflection surface 82, in particular on the surface of the partial area 88', and thus the beam shaping effected by the mirror element 80 in a beam path can be changed.

The embodiments of the present invention described in this specification and the optional features and properties listed in each case in this regard should also be understood to be disclosed in all combinations with one another. In particular, the description of a feature covered by an embodiment - unless explicitly stated to the contrary - is not to be understood here in such a way that the feature is indispensable or essential for the function of the embodiment.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited 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.

Patent Literature Cited

• US10031423B2 [0002]

Claims (15)

Thermally deformable mirror element (80), comprising a mirror body (81) with a deformation layer (86) and a base body (84) and a reflection surface (82) arranged on a surface of the deformation layer (86), the deformation layer (86) made of a deformation material is designed with an expansion coefficient which has a value not equal to zero, and wherein the base body (84) is designed to retain its shape when the deformation layer (86) is heated. Mirror element (80) according to claim 1 , where the expansion coefficient of the deformation material is zero-crossing-free. Mirror element (80) according to one of the preceding claims, wherein the base body (84) is formed from a base material whose coefficient of expansion has a zero crossing at a zero crossing temperature. Mirror element (80) according to one of the preceding claims, wherein the base body (84) comprises a cooling layer (90) with a plurality of cooling channels (92) arranged next to one another for conducting a cooling medium. Mirror element (80) according to claim 4 , wherein the cooling layer (90) is arranged adjacent to the deformation layer (86). Mirror element (80) according to one of the preceding claims, wherein the deformation layer (86) has a plurality of partial regions (88) arranged next to one another in a direction parallel to the reflection surface (82) and thermally insulated from one another. Mirror element (80) according to one of the preceding claims, wherein the deformation layer (86) is attached to the base body (84) by means of joining. Mirror element (80) according to one of the preceding claims, wherein the coefficient of expansion of the deformation material changes by more than 1 K, preferably by more than 4 K, more preferably by more than 7 K, in the event of a temperature change within a temperature range of 20 °C to 80 °C by less than 5%/K, preferably by less than 3%/K, more preferably by less than 1.5%/K, particularly preferably by less than 1%/K. Mirror element (80) according to one of the preceding claims, wherein the coefficient of expansion of the deformation material is at most 20·10 ^-6 K ^-1 . Mirror element (80) according to one of the preceding claims, wherein the reflection surface (82) is designed to reflect radiation with a wavelength between 5 nm and 100 nm and/or between 100 nm and 300 nm. Mirror element (80) according to one of the preceding claims, in which the deformation material is a ceramic or a metallic deformation material. Mirror element (80) according to one of the preceding claims, in which the deformation material is an amorphous or a crystalline deformation material. Use of a mirror element (80) according to one of the preceding claims in a mirror (8), in particular a mirror (8) of a lithography system (1). Thermal deformation system (20) comprising a mirror element (80) according to any one of Claims 1 until 12 and a heating device (21) for heating at least one region (22) of the deformation layer (86). Lithography system (1) comprising a mirror element (80) according to one of Claims 1 until 12 and/or comprising a thermal deformation system (20) according to Claim 14 .

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