DE102019217530A1 - OPTICAL ELEMENT AND METHOD FOR PRODUCING AN OPTICAL ELEMENT - Google Patents

Abstract

An optical element (200, 220, 230) for a lithography system (100A, 100B), comprising: an optical surface (201); a first layer (202) made of a first material with a first coefficient of thermal expansion; a second layer (203) a second material having a second coefficient of thermal expansion greater than the first coefficient of thermal expansion, the first and second layers (202, 203) being assembled along an interface (205) and the first layer (202) between the optical surface (201) and the interface (205) is arranged; anda cooling device (206) which runs in the region of the interface (205) and is designed to cool the optical element (200, 220, 230); wherein the first coefficient of thermal expansion is at least ten times, in particular at least eighty times less than the second coefficient of thermal expansion.

Description

The present invention relates to an optical element, a lithography system with such an optical element and a method for producing such an optical element.

Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out with a lithography system which has an illumination system and a projection system. The image of a mask (reticle) illuminated by means of the illumination system is here projected by means of the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example a silicon wafer, around the mask structure onto the light-sensitive coating of the substrate transferred to.

Driven by the pursuit of ever smaller structures in the manufacture of integrated circuits, EUV lithography systems are currently being developed which use light with a wavelength in the range from 0.1 nm to 30 nm, in particular 13.5 nm. In such EUV lithography systems, because of the high absorption of most materials by light of this wavelength, reflective optics, that is to say mirrors, have to be used instead of — as before — refractive optics, that is to say lenses.

With such mirrors it can happen that about a third of the incident light is absorbed on the mirror surface. This causes strong temperature changes in the EUV optics, which results in thermal expansion or deformation of the mirrors. This affects the imaging properties of the entire optical system and leads to considerable optical aberrations which have an image-deteriorating effect.

As is known, EUV mirrors made of materials with particularly low thermal expansion coefficients are used to reduce the optical aberrations, such as, for example, ULE® material (Ultra Low Expansion) or Zerodur® material. However, such materials are particularly complex to produce and therefore expensive.

From the DE 10 2018 208 783 A1 it is also known to provide cooling channels within the EUV mirror, through which coolant flows for cooling the mirror.

Against this background, it is an object of the present invention to provide an improved optical element with which thermally induced deformations can be prevented.

• eine optische Oberfläche;
• eine erste Schicht aus einem ersten Material mit einem ersten thermischen Ausdehnungskoeffizienten;
• eine zweite Schicht aus einem zweiten Material mit einem zweiten thermischen Ausdehnungskoeffizienten, der größer als der erste thermische Ausdehnungskoeffizient ist, wobei die erste und die zweite Schicht entlang einer Grenzfläche zusammengesetzt sind und die erste Schicht zwischen der optischen Oberfläche und der Grenzfläche angeordnet ist; und
• eine Kühleinrichtung, die im Bereich der Grenzfläche verläuft und eingerichtet ist, das optische Element zu kühlen; wobei
• der erste thermische Ausdehnungskoeffizient mindestens zehn Mal, insbesondere mindestens achtzig Mal, geringer als der zweite thermische Ausdehnungskoeffizient ist.

According to a first aspect, an optical element for a lithography system is proposed. The optical element includes:

• an optical surface;
• a first layer of a first material with a first coefficient of thermal expansion;
• a second layer of a second material having a second coefficient of thermal expansion greater than the first coefficient of thermal expansion, the first and second layers being assembled along an interface and the first layer disposed between the optical surface and the interface; and
• a cooling device which runs in the region of the interface and is set up to cool the optical element; in which
• the first coefficient of thermal expansion is at least ten times, in particular at least eighty times, less than the second coefficient of thermal expansion.

The optical element comprises in particular two layers or sections made of materials with different coefficients of thermal expansion. A cooling device can be arranged between the two layers, which serves to thermally decouple the two layers from one another. Therefore, there is the particular advantage that both layers of the optical element do not have to be made from an expensive material with a low coefficient of thermal expansion (first material). The layer (second layer) that is farther from the optical surface can be made of a cheaper material with a somewhat larger coefficient of thermal expansion, without increasing the deformations compared to an optical element that is formed exclusively from the first material.

The optical surface is, in particular, the surface of the optical element that is struck by light when used in the lithography system. The optical surface can thus be the surface of the optical system that is optically loaded.

In particular, the first layer made of the first material extends between the optical surface and the interface. The second layer can extend on the other side of the interface. The interface, for example, runs parallel to the optical surface. Between the Boundary surface and the surface can also be an angle of up to 5 °.

In this application, the coefficient of thermal expansion, also known as the coefficient of thermal expansion or thermal expansion, is to be understood as the linear coefficient of thermal expansion.

The cooling device runs in the area of the interface. “In the area” of the interface means in particular that a distance between the cooling device and the interface is small, preferably less than 10 mm. The cooling device runs, for example, along the interface and / or touches it.

The cooling device can efficiently dissipate energy absorbed by the optical element, which has converted into heat, and thus reduce the deformation of a given material under a given load. By inserting the cooling device, for example, more absorbed light can be absorbed without increasing the level of aberration. As a result, the optical element can be used, for example, in a lithography system which is operated at a higher power in order, for example, to achieve better throughput and / or higher resolution through lower error contributions from the coating stochastics.

The location of the cooling device between the first and the second layer in particular serves to decouple the second layer from the heat generated on the optical surface. In the first layer, the temperature gradients can be reduced due to the first material used with a low thermal expansion coefficient. In the second layer, the cooling device can achieve a greater reduction in the temperature gradient by up to two orders of magnitude.

The first material plays off components with positive and negative coefficients of thermal expansion. The result is in particular an effectively non-linear relationship between thermal expansion and temperature, whereby there is exactly one temperature value at which the thermal expansion disappears completely in the first material: the zero crossing temperature (in English also "zero crossing temperature").

Due to the greater reduction of the temperature gradient by the cooling device, a material (second material) can be used on the side of the interface facing away from the optical surface that has a higher coefficient of thermal expansion without having any negative effects on the optical aberration. Materials with higher coefficients of thermal expansion are less expensive than materials with lower coefficients of thermal expansion, so that overall an inexpensive optical element can be produced.

Without a cooling device and with a first layer made of the same material as the second layer, the deformation contribution D ₁ from the optical element can be expressed as D ₁ = α ₁ ΔT ₁ , where α _{1 is} the thermal expansion coefficient of the optical element and ΔT _{1 is} the temperature difference in the optical element Element called. For the non-linear material with zero crossing temperature mentioned above, such a relationship applies in the vicinity (mathematically “environment”) of an operating point temperature that is not precisely identical to the zero crossing temperature.

For the optical element according to the first aspect, that is to say with a cooling device and with a second layer made of a material with a higher coefficient of thermal expansion than the material of the first layer, the deformation contribution D ₂ can be expressed as follows: $${\text{D}}_2={\mathrm{\alpha }}_2\Delta {\text{T}}_2\approx \left(100{\mathrm{\alpha }}_1\right)\left(\Delta {\text{T}}_1/100\right)\approx {\mathrm{\alpha }}_1\Delta {\text{T}}_{\text{1}}={\text{D}}_1,$$

The above calculation is an estimate for comparing the orders of magnitude and not a result of a precise simulation. The cooling elements thus make it possible, in particular with comparable deformations and thus a comparable illustration contribution, to replace more expensive material with less expensive material.

The first thermal expansion coefficient is in particular at least ten (10) times lower than the second thermal expansion coefficient, so that a sufficiently low thermal expansion of the optical system is achieved. In other embodiments, the first coefficient of thermal expansion is at least fifty (50), eighty (80), or even a hundred (100) times less than the second coefficient of thermal expansion. This enables a lower thermal expansion of the optical system to be achieved, which also keeps optical aberrations small.

In one embodiment, the optical element is a mirror and the optical surface is a mirror surface.

According to a further embodiment, the cooling device comprises at least one cooling channel through which a coolant can flow.

The cooling channel or channels can run in a straight line and parallel to the optical surface. she run in particular from one side surface of the optical element to the other in order to achieve uniform cooling.

The cross-sectional shape of a cooling channel is preferably round or oval, but other shapes are also conceivable. The diameter of a cooling channel is, for example, 1 to 10 mm, preferably 3 to 6 mm.

In particular, the cooling channel is milled into the first and / or second layer or engraved (for example with a laser). For example, the cooling channel can be ground and / or lapped and polished using a shape-specific tool. The polishing serves in particular to ensure that no residues of the cooling medium adhere to the surface of the cooling channel.

According to a further embodiment, the coolant comprises water, air, hydrogen, nitrogen, helium and / or carbon dioxide. Other fluid materials can also be used as coolants as long as they do not damage the optical element or the lithography system. For example, oils are not suitable as coolants.

The temperature of the coolant as it flows through the cooling channels can depend on the coolant used. When using water, it can be directed through the cooling channels at 22 ° C, for example. For gases, significantly lower temperatures (down to -70 ° C) are also conceivable as long as the material tensions can withstand such temperatures.

According to a further embodiment, the first material is an ultra low expansion material (ULE®), which has a first coefficient of thermal expansion between 5 ° C. and 35 ° C. of a maximum of 0 ± 30 × 10 ^-9 / K. Alternatively, the first material is a Zerodur® material, which has a first coefficient of thermal expansion between 0 ° C and 50 ° C of a maximum of 0 ± 0.100 × 10 ^-6 / K.

According to a further embodiment, a thickness of the first layer is less than a thickness of the second layer. In particular, the thickness of the first layer is at least four times less than the thickness of the second layer.

According to a further embodiment, a distance between the optical surface and the interface is less than 100 mm, preferably less than 50 mm, further preferably less than 20 mm. In preferred embodiments, the distance between the optical surface and the interface is between 10 and 15 mm.

The interface is in particular as close as possible to the optical surface in order to keep the amount of expensive first material low.

At the same time, preference is given to ensuring that the distance between the optical surface and the interface is large enough. In particular, there are two reasons for a minimum distance. On the one hand, the optical surface is measured interferometrically during shaping. An insufficiently damped back reflection from the cooling structures would distort the interferogram. On the other hand, there may be minor pressure fluctuations in the cooling channels of the cooling device during operation. In order that these do not push through as local deformations on the surface, a compensating material thickness is particularly preferred.

According to a further embodiment, a temperature change in the first material with the same surface radiation is two to five times greater than a temperature change in the second material. In other words, the first material heats 2 to 5 times more than the second material when both materials are exposed to the same surface radiation (stress).

According to a further embodiment, a temperature gradient in the first material with the same surface irradiation is two to five times higher than a temperature gradient in the second material. In other words, the temperature dissipation in the first material is 2 to 5 times higher than in the second material if both materials are exposed to the same surface radiation (stress).

According to a further embodiment, the interface runs essentially parallel to the optical surface.

According to a further embodiment, the lithography system is an EUV lithography system, in particular an EUV lithography system for wavelengths below 120 nm, in particular for wavelengths of 13.5 nm.

• Bereitstellen einer ersten Schicht aus einem ersten Material mit einem ersten thermischen Ausdehnungskoeffizienten;
• Bereitstellen einer zweiten Schicht aus einem zweiten Material mit einem zweiten thermischen Ausdehnungskoeffizienten, der größer als der erste thermische Ausdehnungskoeffizient ist;
• Zusammensetzen der ersten und der zweiten Schicht entlang einer Grenzfläche, so dass die erste Schicht zwischen der optischen Oberfläche und der Grenzfläche angeordnet ist, und so dass eine Kühleinrichtung im Bereich der Grenzfläche verläuft, welche eingerichtet ist, das optische Element zu kühlen; wobei
• der erste thermische Ausdehnungskoeffizient mindestens zehn Mal, insbesondere mindestens achtzig Mal, geringer als der zweite thermische Ausdehnungskoeffizient ist.

According to a second aspect, a method for producing an optical element for a lithography system according to the first aspect or according to an embodiment of the first aspect is proposed, the optical element having an optical surface. The process includes:

• Providing a first layer of a first material with a first coefficient of thermal expansion;
• Providing a second layer of a second material with a second thermal Expansion coefficient that is greater than the first thermal expansion coefficient;
• Assembling the first and second layers along an interface, so that the first layer is arranged between the optical surface and the interface, and so that a cooling device extends in the region of the interface, which is set up to cool the optical element; in which
• the first coefficient of thermal expansion is at least ten times, in particular at least eighty times, less than the second coefficient of thermal expansion.

The embodiments and features described for the optical element apply correspondingly to the proposed method and vice versa.

• Einarbeiten eines Kühlkanals und/oder eines Kühlkanalabschnitts in eine Oberfläche der ersten und/oder der zweiten Schicht; und
• anschließendes Zusammensetzen der ersten und der zweiten Schicht entlang der Grenzfläche, so dass der eingearbeitete Kühlkanal und/oder Kühlkanalabschnitt durch das Zusammensetzen die Kühleinrichtung ausbildet.

According to one embodiment, the method further comprises the steps:

• Incorporating a cooling channel and / or a cooling channel section into a surface of the first and / or the second layer; and
• subsequent assembly of the first and second layers along the interface, so that the incorporated cooling duct and / or cooling duct section forms the cooling device by the assembly.

The incorporation of a cooling channel and / or a cooling channel section can take place in the surface of the first and / or second layer, whereby the manufacture is facilitated. In particular, the cooling duct and / or the cooling duct section is milled into the layer surface or engraved (for example with a laser). As previously described, the cooling channel can be ground and / or lapped and polished, for example, using a shape-bound tool. The polishing serves in particular to ensure that no residues of the cooling medium adhere to the surface of the cooling channel.

The cooling channel and / or the cooling channel section can be incorporated as a groove in one or both layers. When the two layers are put together, a groove from the first layer can lie opposite a groove from the second layer, so that both grooves together form the cooling device. It is also possible for the groove of one layer to rest on a non-machined surface of the other layer when it is being assembled, so that it forms a groove with the opposite surface of the other layer as the cooling device.

The grooves can be semi-circular or rectangular. This then results in a cooling device with a round or rectangular cross section. Since the cooling channel does not have to have any optical properties, the cooling channel surface can also have slight irregularities. The cooling channel surface is in particular smooth enough that the coolant flowing through does not cause any vibrations of the optical element.

The first and second layers can be assembled along the interface, for example by joining or cracking.

For example, an alternative way to incorporate the cooling channels of the cooling device into the optical element would be to drill the cooling channels into the finished optical element after the first and second layers have been joined. However, this process is more complex than the surface treatment described above.

According to a further embodiment, the assembly comprises joining and / or wringing the first and second layers.

According to a third aspect, a lithography system is proposed which comprises an optical element according to the first aspect or according to an embodiment of the first aspect. In particular, the optical element is part of the projection exposure system of the lithography system.

The embodiments and features described for the optical element apply correspondingly to the proposed lithography system and vice versa.

In the present case, “a” is not necessarily to be understood as restricting to exactly one element. Rather, several elements, such as two, three or more, can also be provided. Nor is any other measure word used here to be understood to mean that there is a restriction to exactly the number of elements mentioned. Rather, numerical deviations upwards and downwards are possible, unless stated otherwise.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with reference to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

• 1A zeigt eine schematische Ansicht einer Ausführungsform einer EUV-Lithographieanlage;
• 1B zeigt eine schematische Ansicht einer Ausführungsform einer DUV-Lithographieanlage;
• 2 zeigt eine Ansicht eines optischen Elements gemäß einer ersten Ausführungsform;
• 3 zeigt eine Schnittansicht des optischen Elements gemäß der ersten Ausführungsform;
• 4 zeigt eine weitere Schnittansicht des optischen Elements gemäß der ersten Ausführungsform;
• 5 zeigt ein simuliertes Temperaturprofil in einem bekannten optischen Element ohne Kühleinrichtung;
• 6 zeigt ein simuliertes Temperaturprofil in dem optischen Element gemäß der ersten Ausführungsform;
• 7 zeigt ein Verfahren zum Herstellen eines optischen Elements;
• 8 und 9 zeigen einzelne Schritte des Verfahrens zum Herstellen des optischen Elements;
• 10 zeigt eine Schnittansicht eines optischen Elements gemäß einer zweiten Ausführungsform; und
• 11 zeigt eine Schnittansicht eines optischen Elements gemäß einer dritten Ausführungsform.

Further advantageous refinements and aspects of the invention are the subject of the subclaims and those described below Embodiments of the invention. The invention is explained in more detail below on the basis of preferred embodiments with reference to the attached figures.

• 1A shows a schematic view of an embodiment of an EUV lithography system;
• 1B shows a schematic view of an embodiment of a DUV lithography system;
• 2 shows a view of an optical element according to a first embodiment;
• 3 shows a sectional view of the optical element according to the first embodiment;
• 4 shows a further sectional view of the optical element according to the first embodiment;
• 5 shows a simulated temperature profile in a known optical element without a cooling device;
• 6 shows a simulated temperature profile in the optical element according to the first embodiment;
• 7 shows a method for manufacturing an optical element;
• 8th and 9 show individual steps of the method for producing the optical element;
• 10 shows a sectional view of an optical element according to a second embodiment; and
• 11 shows a sectional view of an optical element according to a third embodiment.

In the figures, elements that are the same or have the same function have been given the same reference numerals, unless stated otherwise. It should also be noted that the representations in the figures are not necessarily to scale.

1A shows a schematic view of an EUV lithography system 100A which is a beam shaping and lighting system 102 and a projection system 104 includes. EUV stands for “extreme ultraviolet” (English: extreme ultraviolet, EUV) and denotes a wavelength of the working light between 0.1 nm and 30 nm. The beam shaping and lighting system 102 and the projection system 104 are each provided in a vacuum housing, not shown, each vacuum housing being evacuated with the aid of an evacuation device, not shown. The vacuum housing is surrounded by a machine room, not shown, in which drive devices are provided for the mechanical movement or adjustment of optical elements. Furthermore, electrical controls and the like can also be provided in this machine room.

The EUV lithography system 100A has an EUV light source 106A on. As an EUV light source 106A For example, a plasma source (or a synchrotron) can be provided, which radiation 108A in the EUV range (extremely ultraviolet range), for example in the wavelength range from 5 nm to 20 nm. In the beam shaping and lighting system 102 becomes the EUV radiation 108A bundled and the desired operating wavelength from the EUV radiation 108A filtered out. The one from the EUV light source 106A generated EUV radiation 108A has a relatively low air transmittance, which is why the beam guiding rooms in the beam shaping and lighting system 102 and in the projection system 104 are evacuated.

This in 1A shown beam shaping and lighting system 102 has five mirrors 110 . 112 . 114 . 116 . 118 on. After passing through the beam shaping and lighting system 102 becomes the EUV radiation 108A passed onto a photomask (reticle) 120. The photomask 120 is also designed as a reflective optical element and can be used outside of the systems 102 . 104 be arranged. The EUV radiation can further 108A by means of a mirror 122 on the photomask 120 be directed. The photomask 120 has a structure, which by means of the projection system 104 scaled down to a wafer 124 or the like is mapped.

The projection system 104 (also called a projection lens) has six mirrors M1 to M6 for imaging the photomask 120 on the wafer 124 on. Individual mirrors can be used M1 to M6 of the projection system 104 symmetrical to an optical axis 126 of the projection system 104 be arranged. It should be noted that the number of mirrors M1 to M6 the EUV lithography system 100A is not limited to the number shown. There may also be more or fewer mirrors M1 to M6 be provided. Furthermore, the mirrors M1 to M6 usually curved at the front for beam shaping.

1B shows a schematic view of a DUV lithography system 100B which is a beam shaping and lighting system 102 and a projection system 104 includes. DUV stands for "deep ultraviolet" (English: deep ultraviolet, DUV) and denotes a wavelength of the working light between 30 nm and 250 nm. The beam shaping and lighting system 102 and the projection system 104 can - as already related to 1A described - arranged in a vacuum housing and / or surrounded by a machine room with appropriate drive devices.

The DUV lithography system 100B has a DUV light source 106B on. As a DUV light source 106B For example, an ArF excimer laser can be provided, which radiation 108B emitted in the DUV range at, for example, 193 nm.

This in 1B shown beam shaping and lighting system 102 conducts the DUV radiation 108B on a photomask 120 , The photomask 120 is designed as a transmitting optical element and can be used outside of the systems 102 . 104 be arranged. The photomask 120 has a structure, which by means of the projection system 104 scaled down to a wafer 124 or the like is mapped.

The projection system 104 has multiple lenses 128 and / or mirror 130 for imaging the photomask 120 on the wafer 124 on. Individual lenses 128 and / or mirror 130 of the projection system 104 symmetrical to an optical axis 126 of the projection system 104 be arranged. It should be noted that the number of lenses 128 and mirror 130 the DUV lithography system 100B is not limited to the number shown. You can also use more or fewer lenses 128 and / or mirror 130 be provided. Furthermore, the mirrors 130 usually curved at the front for beam shaping.

An air gap between the last lens 128 and the wafer 124 can by a liquid medium 132 be replaced, which has a refractive index> 1. The liquid medium 132 can be high-purity water, for example. Such a structure is also known as immersion lithography and has an increased photolithographic resolution. The medium 132 can also be called immersion liquid.

2 shows a view of an optical element 200 according to a first embodiment. With the optical element 200 it is one of the mirrors 110 . 112 . 114 . 116 . 118 . M1 - M6 the EUV lithography system 100A or around the mirror 130 the DUV lithography system 100B , The mirror 200 has a diameter of 500 mm (basically other diameters between 200 and 1500 mm are also conceivable).

The mirror 200 is about fasteners 211 inside the lithography system 100A or 100B attached. The mirror 200 comprises a structural body 212 and a coating 213 on an optical surface 201 of the structural body 212 , The coating 213 is made of a reflective material on which the light source 106A . 106B emitted light occurs and is reflected. The surface 201 is slightly curved inwards. In alternative embodiments, the mirror 200 convex shape.

Part of the surface 201 light is not reflected, but on the mirror surface 201 absorbed. This absorption leads to temperature changes in the mirror 200 , which are undesirable because they lead to significant optical aberrations that affect the imaging quality of the lithography system 100A . 100B influence negatively.

The 3 shows a central section of the mirror 200 the 2 along the XY plane. Like in the 3 shown is the mirror 200 through a first layer 202 and a second layer 203 formed which is parallel to the optical surface 201 run and at an interface 205 are composed. The first layer 202 extends between the optical surface 201 and the interface 205 , The first layer extends along the Y direction 202 above the second layer 203 ,

Along the interface 205 extends a cooling device 206 that have a variety of cooling channels 207 having. In the 3 are just two cooling channels 207 provided with reference numerals, but they are all identical. The cooling channels 207 have a round cross-section and a diameter of 4 mm. The cooling channels are in operation 207 flows through a coolant, which is water at 22 ° C in the present example.

The fat D1 the first layer 202 (along the Y axis) is less than the thickness D2 the second layer 203 (along the Y axis). The fat D1 in the example is 3 12 mm, the thickness D2 is 40 mm. The total thickness of the mirror D1 + D2 is thus 52 mm. The distance between the optical surface 201 and the cooling device 206 is 12 mm.

The first layer 202 is made of a first material, which is Ultra Low Expansion Material (ULE®) and has a first coefficient of thermal expansion between 5 ° C and 35 ° C of a maximum of 0 ± 30 × 10 ^-9 / K. The second layer 203 is made of a second material, which is quartz glass and has a second coefficient of thermal expansion at 20 ° C of 0.54 x 10 ^-6 / K.

The first coefficient of thermal expansion is thus significantly lower than the second coefficient of thermal expansion. The first layer 202 serves to reduce the temperature gradients due to the first material used low coefficient of thermal expansion. In the second shift 203 thanks to the cooling device 206 achieved a greater reduction in the temperature gradient by up to two orders of magnitude.

Due to the greater reduction in the temperature gradient by the cooling device 206 can below the cooling device 206 a second material can be used, which has a higher coefficient of thermal expansion than the first material, without having negative effects on the optical aberration. Materials with higher coefficients of thermal expansion are cheaper than materials with lower coefficients of thermal expansion, so that the second material is inexpensive relative to the first material. Overall, this makes a cheaper mirror 200 manufactured.

4 shows a further sectional view of the optical element 200 according to the first embodiment. When viewing the 4 is a cut of the mirror 200 the 2 along the curved surface along which the interface is located 205 extends.

In the 4 can be seen how the cooling channels 207 the cooling device 206 inside the mirror 200 run. The cooling channels 207 extend parallel to each other along the Z axis and open laterally in side channels 214 , The cooling water K is through a coolant inlet 208 in the cooling device 206 in and through a coolant outlet 209 from the cooling device 206 led out.

The 5 shows a simulated temperature profile in a known optical element 240 without cooling device. The optical element 240 is a mirror according to the state of the art, which is made exclusively from ULE® material and not a cooling device 206 having. In the 5 designate T1 - T9 temperature ranges, whose temperature limits in the right part of the 5 are shown.

In the depth of the mirror 240 (along the Y axis) the temperature drops to approximately 22.75 ° C to 22.5 ° C.

6 shows a simulated temperature profile in the mirror 200 according to the first embodiment, which is based on the 2 to 4 has been described and two layers 202 . 203 made of materials with different coefficients of thermal expansion and the cooling device 206 having. In the 6 T1 - T9 denote the same temperature ranges as in 5 ,

Like in the 6 visible, temperatures of ~ 22.5 ° C occur directly below the cooling channels. In the depth of the mirror 200 (along the Y axis) the temperature drops to around 22 ° C. With the mirror 200 can one opposite the mirror 240 state of the art increased temperature reduction can be achieved.

7 shows a method for manufacturing an optical element 200 , That in the 7 The method described is used, for example, to manufacture the mirror 200 from the 2 to 4 ,

In one step S1 becomes the first layer 202 provided. In one step S4 becomes the first layer 202 edited by cooling duct sections 210 (hereinafter also referred to as “grooves”) along the surface 215 that of the optical surface 201 is turned away. This is in the upper part of the 8th shown.

In one step S2 becomes the second layer 203 provided. In one step S4 becomes the second layer 203 edited by cooling duct sections 210 along the surface 216 be milled. This is in the lower part of the 8th shown.

Like in the 8th can be seen, the same number of grooves 210 in the first and in the second layer 202 . 203 milled. The grooves 210 each have a semicircular cross-section and are arranged at equal distances from each other. The grooves 210 are positioned so that the grooves 210 the first layer 202 and the grooves 210 the second layer 203 each other when joining the two layers 202 . 203 compared to lie.

In one step S3 ( 7 ) become the two layers 202 . 203 composed. This is done by starting. The two faces 215 and 216 cleaned and pressed together at room temperature. For better strength, the cracking or joining can also take place at an elevated temperature at which the boundary material is easily melted.

As a result, the mirror 200 to 9 get the same properties as the mirror 200 the 2 - 4 has (including the curvature, which is used to simplify the drawings in the 8th and 9 is not visible).

The 10 shows a side view of an optical element 220 according to a second embodiment. The optical element 220 is also a mirror for the lithography system 100A . 100B , The mirror 220 differs only in the position of the cooling channels 207 the cooling device 206 from the mirror 200 according to the first embodiment. The cooling ducts are actually located 207 in the mirror 220 according to the second embodiment along the Y direction above the interface 205 , The distance between the optical surface 201 and the cooling device 206 here is 9 mm (D1 still being 12 mm).

The cooling channels 207 are completely in the first shift 202 embedded. To make the mirror 220 first be the two layers 202 . 203 composed. Then the cooling channels are formed 207 Holes through the first layer 202 drilled. Compared to the manufacturing process of 7 becomes the step S4 only after assembling S3 carried out.

The 11 shows a side view of an optical element 230 according to a third embodiment. The optical element 230 is also a mirror for the lithography system 100A . 100B , The mirror 230 differs only in the position of the cooling channels 207 the cooling device 206 from the mirror 200 according to the first embodiment. The cooling ducts are actually located 207 in the mirror 230 according to the third embodiment along the Y direction below the interface 205 , The distance between the optical surface 201 and the cooling device 206 here is 15 mm (D1 still being 12 mm).

The cooling channels 207 are completely in the second layer 203 embedded. To make the mirror 230 first be the two layers 202 . 203 composed. Then the cooling channels are formed 207 Holes through the second layer 203 drilled. Compared to the manufacturing process of 7 becomes the step S4 only after assembling S3 carried out.

Although the present invention has been described on the basis of exemplary embodiments, it can be modified in many ways. For example, other materials can be used to make the first and second layers 202 . 203 be used as long as their thermal expansion coefficients meet the requirements described. Furthermore, the number of cooling channels 207 be changed in the cooling device and in particular with regard to the diameter of the cooling channels 207 vary. The distances between the cooling channels 207 , the thickness of the layers 202 . 203 and the depth of the cooler 206 under the optical surface 201 can be changed within the scope of the disclosure.

LIST OF REFERENCE NUMBERS

100A

EUV lithography system

100B

DUV lithography system

102

Beam shaping and lighting system

104

projection system

106A

EUV-light source

106B

DUV light source

108A

EUV radiation

108B

DUV radiation

110

mirror

112

mirror

114

mirror

116

mirror

118

mirror

120

photomask

122

mirror

124

wafer

126

optical axis

128

lens

130

mirror

132

medium

200

optical element

201

optical surface

202

first layer

203

second layer

205

interface

206

cooling device

207

cooling channel

208

Coolant inlet

209

coolant outlet

210

groove

211

fastener

212

body structure

213

coating

214

side channel

215,216

surface

220

optical element

230

optical element

240

optical element

D1

Thickness of the first layer

D2

Thickness of the second layer

M1

mirror

M2

mirror

M3

mirror

M4

mirror

M5

mirror

M6

mirror

K

coolant

S1 - S4

steps

T1-T9

temperature

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 102018208783 A1 [0006]

Claims (14)

Optical element (200, 220, 230) for a lithography system (100A, 100B), comprising: an optical surface (201); a first layer (202) of a first material with a first coefficient of thermal expansion; a second layer (203) made of a second material with a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion, the first and second layers (202, 203) being assembled along an interface (205) and the first layer ( 202) is arranged between the optical surface (201) and the interface (205); and a cooling device (206) which runs in the region of the interface (205) and is designed to cool the optical element (200, 220, 230); in which the first coefficient of thermal expansion is at least ten times, in particular at least eighty times, less than the second coefficient of thermal expansion. Optical element after Claim 1 , which is a mirror and wherein the optical surface (201) is a mirror surface. Optical element after Claim 1 or 2 , wherein the cooling device (206) comprises at least one cooling channel (207) through which a coolant can flow. Optical element after Claim 2 , wherein the coolant comprises water, air, hydrogen, nitrogen, helium and / or carbon dioxide. Optical element according to one of the Claims 1 to 4 , wherein the first material is an Ultra Low Expansion Material (ULE®), which has a first thermal expansion coefficient between 5 ° C and 35 ° C of a maximum of 0 ± 30 × 10 ^-9 / K or wherein the first material is a Zerodur® Material that has a first coefficient of thermal expansion between 0 ° C and 50 ° C of a maximum of 0 ± 0.100 × 10 ^-6 / K. Optical element according to one of the Claims 1 to 5 , wherein a thickness (D1) of the first layer (202) is less than a thickness (D2) of the second layer (203). Optical element according to one of the Claims 1 to 6 , wherein a distance between the optical surface and the interface is less than 100 mm, preferably less than 50 mm, further preferably less than 20 mm. Optical element according to one of the Claims 1 to 7 , wherein a temperature change with the same surface radiation in the first material is two to five times greater than a temperature change in the second material. Optical element according to one of the Claims 1 to 8th , wherein the interface (205) runs essentially parallel to the optical surface (201). Optical element according to one of the Claims 1 to 9 , wherein the lithography system (100A) is an EUV lithography system, in particular an EUV lithography system for wavelengths below 120 nm. Method for producing an optical element (200, 220, 230) for a lithography system (100A, 100B) according to one of the Claims 1 to 10 , wherein the optical element (200, 220, 230) has an optical surface (201), comprising: providing (S1) a first layer (202) made of a first material with a first coefficient of thermal expansion; Providing (S2) a second layer (203) of a second material with a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion; Assembling (S3) the first and second layers (202, 203) along an interface (205) so that the first layer (202) is arranged between the optical surface (201) and the interface (205), and so that a Cooling device (206) runs in the area of the interface (205), which is set up to cool the optical element (200, 220, 230); wherein the first coefficient of thermal expansion is at least ten times, in particular at least eighty times less than the second coefficient of thermal expansion. Procedure according to Claim 11 , comprising: incorporating (S4) a cooling channel (207) and / or a cooling channel section (210) into a surface (215, 216) of the first and / or the second layer (202, 203); and then assembling (S3) the first and second layers (202, 203) along the interface (205) so that the incorporated cooling duct (207) and / or cooling duct section (210) forms the cooling device (206) by the assembling. Procedure according to Claim 12 , wherein the assembly (S3) comprises joining and / or wringing the first and second layers (202, 203). Lithography system with an optical element (200, 220, 230) according to one of the Claims 1 to 10 ,

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