DE102019205265A1 - Method for producing a glass body with cooling channels - Google Patents

Abstract

The invention relates to a method for producing a glass body (1) with at least one cooling channel, preferably with a plurality of cooling channels (2). In one aspect, the method comprises: providing a first partial body (3a) and a second partial body (3b) of the glass body (1), forming at least one cooling channel (2) by in particular mechanical processing of the glass material (4) on a surface (5a) of the first part body (3a) and / or the second part body (3b), as well as production of the glass body (1) by connecting the first part body (3a) to the second part body (3b) on the processed surface (5a) by high temperature bonding. In a second aspect, the method comprises: embedding at least one placeholder (9a-e) made of a temperature-resistant material (10) in the glass material (4) of the glass body (1) during the manufacture of the glass body (1) to form the at least one cooling channel ( 2) in the glass body (1). The invention also relates to a reflective optical element, in particular an EUV mirror, which has a substrate with at least one cooling channel (2) made from such a glass body (1) and an optical arrangement, in particular an EUV lithography system at least one such reflective optical element.

Description

Background of the invention

The invention relates to two methods for producing a glass body which has at least one cooling channel, preferably a plurality of cooling channels. The invention also relates to a reflective optical element, in particular for reflecting EUV radiation, which has a substrate with at least one cooling channel, and an optical arrangement, in particular an EUV lithography system, which comprises at least one such reflective optical element.

In an EUV lithography system, reflective optical elements in the form of mirrors, in particular in the form of mirrors of a projection system, are exposed to a high radiation power, which leads to heating of the mirror or the mirror substrate. The heating of the mirror substrate leads to deformations of the mirror surface, which impair the image quality of the projection system. To counter this problem, substrates made of materials are typically used that have a low coefficient of thermal expansion.

In order to reduce the temperature of the mirrors, it is known to introduce cooling channels into the mirror substrate through which a cooling fluid flows. The production of the cooling channels requires the installation or the introduction of tubes or through channels with a geometry that is dependent on the respective mirror in the substrate. During the processing of the substrate, stresses can occur in the glass material, which can also have an unfavorable effect, since these are caused by the shaping of the mirror, e.g. when milling the mirror surface, can lead to unexpected changes in shape.

In the DE 102017221388 A1 describes a method for producing a component for a lithography system through which a cooling fluid can flow, comprising the steps of: surrounding a tube section that is arranged within a capsule and through which the cooling fluid can flow with a powdery filler material, at least one end of the tube section protruding from the capsule, and manufacturing of the component by hot isostatic pressing of the powdery filler material arranged in the capsule.

In the WO 2012/126830 A1 describes an optical element for a projection exposure system in semiconductor lithography, which has an optically active surface and at least one cooling component for cooling the optical element. The cooling component is connected to at least two separate cooling circuits and is designed in such a way that the optically active surface can be more strongly cooled in at least one sub-area than in a further sub-area.

From the US 7,591,561 B2 a liquid-cooled mirror for EUV lithography has become known in which at least one microchannel is arranged below an optical surface. In one example, a base body is provided in which a microchannel is formed. The base body is coupled or connected to an attachment on a surface on which the microchannel is formed in order to close the microchannel along its circumference.

Object of the invention

The object of the invention is to provide a method for producing a glass body in which the glass material is influenced as little as possible by the introduction of a cooling channel, in particular using a placeholder introduced into the cooling channel.

Subject of the invention

According to a first aspect, this object is achieved by a method of the type mentioned at the outset, comprising: providing a first part body and a second part body of the glass body, forming at least one cooling channel by in particular mechanical processing of the glass material on a surface of the first part body and / or the second Partial body, as well as producing the glass body by connecting the first partial body to the second partial body on the processed surface by high-temperature bonding.

In this aspect of the invention, it is proposed that at least one, usually a plurality of cooling channels be formed in at least one of the two partial bodies, which are subsequently joined together to form the glass body, by mechanical processing, typically by milling. When the two part bodies are connected along the machined surface, the cooling channels are closed along their circumference. When connecting by high-temperature bonding (direct bonding), the two part-bodies are typically heated to a temperature of more than approx. 1000 ° C, usually between approx. 1300 ° C-2000 ° C, so that the part-bodies or the respective surface is melted and the two part bodies connect to one another along the machined surface without the use of a joining agent. The cooling channels can only be formed in the first, lower of the two partial bodies, but it is also possible to form the cooling channels - or a part of the cross section of the cooling channels - in the second, upper partial body or in both partial bodies. When connecting By high-temperature bonding, the second part body is usually placed on the first part body with a surface whose geometry corresponds to that of the machined surface.

In the variants described below, it is assumed that the cooling channels are free of placeholders, tubular bodies, etc. when the glass body is produced by connecting the two part bodies by high-temperature bonding.

In a variant, cooling channels separated from one another by webs are formed during machining, with a web width A in the lateral direction at least 10 times, preferably at least 20 times, particularly preferably at least 50 times, in particular at least 100 times the width B. of a respective cooling channel. The web width A typically corresponds to the lateral or lateral distance A between adjacent cooling channels in a direction transverse to a main direction of the cooling channels, along which the cooling channels extend through the glass material. As a rule, the cooling channels are spaced at a constant distance A, i.e. with constant web width A, introduced into the glass material, but this is not absolutely necessary. The ratio between the web width A and the width B of the cooling channels should be comparatively large in order to avoid that the webs formed between the cooling channels in the glass material widen or tip over during high temperature bonding under the influence of gravity. The width B of the cooling channels should preferably be between approx. 0.5 mm and approx. 3 mm.

In a further variant, the cooling channels are formed during machining with a depth C which is between 2 times and 10 times the width B of a respective cooling channel. This is particularly favorable if the ratio between the web width A and the width B of the cooling channels is comparatively large in order to ensure a sufficient flow of a cooling liquid through the cooling channels.

In a further variant, at least two channel-free areas are formed on the surface during machining, which have a width D in the lateral direction that is at least three times the depth of the cooling channels (D> 3 C) and / or at least five times the web width A of the webs (D> 5 A). In particular in the event that the channel portion is comparatively large, i.e. the ratio between the web width A and the width B of a respective cooling channel is comparatively small (A / B <20) and / or the cooling channels are very deep, so that the ratio between the width B and the depth C of the cooling channels is comparatively small ( B / C <5) it has proven to be advantageous to form at least two channel-free areas which have the width indicated above. The channel-free areas can in particular be formed adjacent to the lateral edges of the surface of the respective partial body, but this is not absolutely necessary.

In a further variant, providing includes dividing the glass body into the first part body and into the second part body along an in particular curved surface. The glass body can be divided up by sawing along a desired, possibly curved, contour. It is possible, for example, by means of ball cutting, to create a curved surface when dividing the glass body. This is particularly advantageous if the glass body is used to produce a mirror substrate, the mirror surface of which is itself curved. In the event that the curvature of the surface produced during dividing essentially corresponds to the curvature of the mirror surface, the cooling channels, which are preferably attached in the vicinity of the mirror surface, can be formed in the glass body at an approximately constant distance from the mirror surface.

In a further variant, a placeholder made of a temperature-resistant material is introduced into a respective cooling channel before the two partial bodies are connected. The use of placeholders is beneficial in order to prevent the webs formed between the cooling channels from widening or tipping over during high-temperature bonding (see above). When using placeholders, it is generally not necessary to adhere to the conditions described above for the web width or the ratio between the web width and the width of the cooling channels, etc., even if this is possible in principle. The placeholder (s) can be removed from the cooling channels after the high-temperature bonding or - in the case of a tubular configuration - can be provided to remain in the glass body or in the respective cooling channel.

Another aspect of the invention relates to a method for producing a glass body with at least one cooling channel, preferably with a plurality of cooling channels, comprising: embedding at least one placeholder made of a temperature-resistant material in the glass material of the glass body during the production of the glass body to form the at least one cooling channel in the vitreous. In this aspect of the invention, it is proposed that the placeholders be embedded in the glass material when the glass body is produced. The prerequisite for this is that the placeholders have a certain robustness. This is usually the case guaranteed if the placeholders consist of a metal or a largely densely sintered ceramic.

In one variant, the method comprises: providing a first part body and a second part body of the glass body, as well as producing the glass body by connecting the first part body to the second part body by high-temperature bonding with the at least one placeholder being embedded between the two part bodies. As in the first aspect, the first and second partial bodies can be provided by dividing the glass body. In contrast to the first aspect, however, in the present case the partial bodies are not or are not mechanically processed in order to introduce or mill in cooling channels, rather the placeholders are introduced or inserted between the two partial bodies prior to the high-temperature bonding. In this case, the placeholders embed themselves in the glass material during high-temperature bonding, although there may be increased bubble formation in the area of the former interface between the part-bodies.

In an alternative variant, the method comprises: depositing glass material on a carrier, embedding the placeholder in the deposited glass material, and cooling the glass material to produce the glass body. In the case of a direct deposition of the glass material, as for example in the US 5,970,751 f For a SiO ₂ -TiO ₂ glass material is described, the titanium-doped glass material is usually deposited in a container or on a carrier, for example in the form of a turntable, of a refractory furnace. With the exception of a few millimeters, the deposited glass material solidifies directly below the hot surface on which it is deposited. If necessary, the placeholders can be placed directly in the container of the refractory furnace if the deposition process is stopped after a certain period of time. In this case, a network of placeholders, for example mechanically stabilized by cross connectors, can be placed on the already solidified glass material and the deposition process can then be continued, so that the placeholders are embedded in the glass material. Alternatively, the placeholder can optionally be introduced before or during the filling of liquid glass material into a container, particularly if the glass material is quartz glass or a glass ceramic, for example Zerodur®. If necessary, the placeholders can be introduced into the container before the glass material is deposited and fixed there in a suitable manner.

In a variant, the placeholder is tubular and remains in the cooling channel after the glass body has been produced. In this case, the cooling liquid is not guided directly through the cooling channel formed in the glass material, but rather through the cavity formed in the tubular placeholder.

In an alternative variant, the placeholder is removed from the glass body after the glass body has been produced in order to form the cooling channel. In this case, the placeholder does not remain in the cooling channel. The cooling liquid is passed directly through the cooling channel and is in contact with the glass material. There are various options for removing the placeholder, several of which are described in detail below.

Most temperature-resistant materials or solid bodies have a higher thermal expansion than the glass material, so that the material of a respective placeholder contracts more than the glass material when it cools. Therefore, the placeholders typically detach themselves from the glass material in an uncontrolled manner over large parts of their circumference during cooling. This is basically favorable for the easier removal of the placeholders. Even before the placeholders are detached, however, local tensile stresses are exerted by the placeholders on the glass material, some of which may no longer be able to relax before complete solidification and are frozen. Such mechanical stresses are unfavorable because when changing the mirror shape, e.g. milling the mirror surface can lead to unexpected changes in shape. Also, due to the uncontrolled detachment of the placeholders from the glass material, the heat transfer and thus the cooling rate are inhomogeneous, which can lead to poorly controlled changes in the homogeneity of the thermal expansion coefficient, because the thermal expansion coefficient depends on the cooling rate, especially in the temperature range between approx. 1300 ° C and 800 ° C dependent. Several possibilities are described below how the introduction of mechanical stresses into the glass material when the placeholders are detached can be avoided or at least reduced. In the event that the cooling channels are introduced into the glass material by milling, the placeholders can optionally be designed to be slightly smaller than the cross section of a respective cooling channel. Suitable dimensions of the cross section of the placeholders can be calculated, for example, by finite element methods.

In one variant, the placeholder has an in particular solid base body, on the circumference of which there are formed lamellae that run in the longitudinal direction and are separated from one another by gaps. In this case, millings running in the longitudinal direction are typically made in a massive placeholder, which are used to form, for example, L- shaped or T-shaped slats. The lamellas can remain connected to the glass material over a large part of their surface by exerting a slight tensile force and only detach via their web or their web-shaped connection to the solid base body. The width of a respective gap between the lamellas can for example be between approx. 0.5 mm and approx. 3 mm.

In a variant, the placeholder is tubular and either has slots spaced from one another or is designed as a spiral tube. In the former case, the slots can for example be designed as longitudinal slots which, however, typically do not extend continuously along almost the entire length of the tubular placeholder, but are arranged offset to one another and only have a comparatively short length so that the tubular placeholder has a maximum maintains tangential cohesion. To avoid the build-up of stresses along the tubular placeholder, the slots can also be slightly coiled. The use of a spiral tube as a tubular placeholder is also possible in principle, but generally leads to increased radial stresses when the placeholder is detached from the glass material.

In a further variant, the placeholder has an in particular massive or largely massive base body that is embedded in a layer that is more flexible or that generates less mechanical stress than the base body when detached, so that the layer can introduce mechanical stresses when the glass material cools down. The layer in which the base body is embedded can be formed, for example, from granules / sand and / or from a solid foam.

In a further variant, the temperature-resistant material of the placeholder has a melting point of more than 1500 ° C., preferably more than 2000 ° C., in particular more than 3000 ° C., and is preferably formed from a metallic material or a semi-metal. As described above, the high-temperature bonding is usually carried out at temperatures of more than 1000 ° C, usually between approx. 1300 ° C or 1500 ° C and 2000 ° C. The production of the glass body by direct deposition is also carried out at correspondingly high temperatures. It is therefore necessary that the temperature-resistant material of the placeholder withstand temperatures of approx. 1300 ° C. to 2000 ° C. and can either serve as a tube itself and remain in the cooling channel, or can be removed from the glass body without damaging the glass material. In addition, only the lowest possible stresses (<2 MPa) should be introduced into the glass material by the placeholder when it cools.

In a further variant, the temperature-resistant material of the placeholder is selected from the group comprising: Ti, Pa, Pt, Zr, Cr, V, Rh, Hf, Tc, Ru, B, Ir, Nb, Mo, Ta, Os, Re, W, C. All these materials have a melting point of more than 1500 ° C: titanium: 1660 ° C, protactinium: 1750 ° C, platinum: 1772 ° C, zirconium 1852 ° C, chromium 1857 ° C, vanadium: 1890 ° C, rhodium: 1966 ° C, hafnium: 2150 ° C, technetium: 2200 ° C, ruthenium: 2250 ° C, boron: 2300 ° C, iridium: 2410 ° C, nobium: 2468 ° C, molybdenum: 2617 ° C, Tantalum: 2996 ° C, osmium: 3045 ° C, rhenium: 3180 ° C, tungsten: 3410 ° C, carbon: 3500 ° C. Most of the above-mentioned materials have in common that they can be used at elevated temperatures, e.g. occur during high-temperature bonding, oxidize or burn.

In a further variant, the production of the glass body, i. the high temperature bonding or the deposition of the glass material, under protective gas, e.g. in a nitrogen atmosphere. As a rule, these processes are not carried out in a protective gas atmosphere. However, these processes must be carried out under protective gas if there is a risk that the material of the placeholder will burn off during the high-temperature bonding or during the deposition of the glass material.

In a further variant, the placeholder contains a non-combustible material, preferably an oxide, in particular an oxide ceramic, or a nitride, or the placeholder is formed from the non-combustible material, preferably an oxide, in particular an oxide ceramic, or a nitride. Most oxide ceramics or nitrides are chemically very stable. Boron nitride or titanium nitride, for example, are suitable for the present application. For example, MgO or CaO are suitable as oxides, the latter in particular also having a high temperature resistance (melting point 2580 ° C.). When using a placeholder made of a material that is non-flammable even at temperatures of more than approx. 1300 ° C, it is generally possible to dispense with the bonding or deposition process in a protective gas atmosphere.

In a further variant, a coating which is inert to oxidation is applied to the (usually combustible) placeholder. The application of a thin surface coating made of a material inert to oxidation, for example platinum or osmium, on a tubular or essentially solid placeholder made of metals other than those mentioned or made of graphite enables the bonding or deposition process to be carried out without protective gas. The coating is usually limited to the circumference of the placeholder, but can also be applied to the end faces at the free ends of the placeholder and - in the case of a tubular placeholder - on its inside.

In a further variant, a coating that is inert to a reaction with the glass material of the glass body is applied to the placeholder or to the wall (s) of the cooling channel. Such a (thin) surface coating is particularly useful in the event that the tubular or essentially solid placeholder is formed from a material that reacts with the glass material of the glass body, for example an oxide ceramic, e.g. CaO or MgO. In the case of calcium oxide ceramics or magnesium oxide ceramics that can be easily removed from the cooling duct with water, there is a risk that they will be incorporated into the glass material without such a coating, since CaO and MgO are components of classic soda-lime glasses. Osmium or platinum, for example, can be used as materials for the coating, which is inert to a reaction with the glass material of the glass body. Platinum wets the glass surface and prevents further reactions, does not react with atmospheric oxygen even at elevated temperatures and is therefore also suitable for preventing oxidation of the material of the placeholder. When using a tubular placeholder, it is sufficient if the coating, which is inert to the reaction with the glass material, is applied only along the outer circumference of the placeholder, since the placeholder only comes into contact with the glass material along its outer circumference. In the event that the cooling channels are mechanically processed, e.g. be introduced into the glass material by milling, the inert coating can also be applied to the wall (s) of the cooling channel.

In a further variant, the placeholder is a pressed or sintered body or a body formed from a mixture connected with a binding agent. A dimensionally stable, porous or pressed or (as a rule roughly or incompletely) sintered body can serve as a placeholder. The use of a body formed from sand or from granules and a binding agent as a placeholder is also possible. Such a body will quickly tear along a roughly tangential line when it cools and therefore cannot exert any major tensile stresses on the glass material when it cools. The removal of such a body is also made easier by the circumferential crack. The bodies described above preferably contain an oxide ceramic or a nitride. For example, the body can be formed from a mixture of a sand of aluminum oxide or of boron nitride with some CaO and / or MgO as a binder.

In a further variant, the placeholder is formed by a granulate or a possibly graded sand made of temperature-resistant material, for example an oxide ceramic or a nitride, which is pressed into the milled cooling channels. Such a placeholder made of sand or granulate that is not too tightly compressed is generally not dimensionally stable and can be easily removed from the cooling channel after the glass material has cooled, for example using a water jet nozzle and / or a mechanical tool, e.g. of a wire.

The placeholders described above in the form of pressed or coarsely sintered bodies or in the form of a mixture connected by means of a binding agent can typically be washed out by a water jet or the like, removed from the cooling channels by ultrasound and / or by using a suitable mechanical tool . When using CaO as a temperature-resistant material, however, it should be noted that CaO reacts strongly exothermically with water, so that the supply of water should be limited when removing the CaO material. In this regard, it is advantageous if CaO is used as a binder in a mixture with a sand, e.g. made of aluminum oxide and / or boron nitride is used. With such a mixture, the CaO content is greatly reduced, so that the development of heat can be controlled and the remaining sand can be rinsed out without any problems. In contrast to CaO, MgO hardly reacts with water, i.e. the shelf life of MgO is greater. The risk of the placeholder reacting with the glass material during bonding is also reduced. However, the comparatively weak reaction of MgO with water is typically sufficient to sufficiently reduce the strength of a body made of a lightly bound mixture so that it can be flushed out of the cooling duct with the aid of a water jet nozzle.

• Bei einer Variante erfolgt das Entfernen des Platzhalters durch Abbrennen des Platzhalters unter Zuführung eines oxidierenden Gases, insbesondere von Sauerstoff. Das Abbrennen ist bei den meisten der weiter oben beschriebenen Platzhalter aus metallischen oder halbmetallischen Materialien möglich und bietet sich insbesondere bei Kohlenstoff als temperaturbeständigem Material an. Das Glasmaterial sollte beim Abbrennen des Platzhalters nicht auf Temperaturen von mehr als ca. 600°C erwärmt werden. Dies kann durch die Begrenzung der Sauerstoff-Zufuhr und ggf. lokale Zufuhr von Sauerstoff über eine Sonde erreicht werden.

In the case of placeholders, where the temperature-resistant material is not granular but massive, there are also various options for removing them from the cooling channels:

• In a variant, the placeholder is removed by burning off the placeholder while supplying an oxidizing gas, in particular oxygen. Burning off is possible with most of the above-described placeholders made of metallic or semi-metallic materials and is particularly suitable for carbon as a temperature-resistant material. The glass material should not open when the placeholder burns down Temperatures of more than approx. 600 ° C are heated. This can be achieved by limiting the oxygen supply and, if necessary, local supply of oxygen via a probe.

In a further variant, the preferably metallic placeholder is removed by electrochemical removal and / or by an etching treatment using an etchant. During electrochemical ablation, the usually metallic placeholder is polarized as the anode and the tool as the cathode. In the etching treatment, the etchant is selected depending on the type of temperature-resistant material. For example, tungsten can be dissolved in a mixture of sodium nitrate and sodium carbonate or similar alkali metal salts heated to approx. 400 ° C-600 ° C. Titanium can e.g. be dissolved in concentrated sulfuric acid, which does not attack the glass material.

In a further variant, the glass material of the glass body is formed from quartz glass, preferably from titanium-doped quartz glass, or from a glass ceramic, for example from Zerodur®. Titanium-doped quartz glass, which is sold, for example, by the Corning company under the trade name ULE®, and certain glass ceramics, for example Zerodur®, have a particularly low coefficient of thermal expansion and are therefore particularly suitable for the production of substrates for EUV mirrors. In the so-called direct deposition of titanium-doped quartz glass (SiO ₂ -TiO ₂ glass), the glass material is usually deposited on a carrier of a refractory furnace, as is the case, for example, in FIG U.S. 5,970,751 is described. In the event that the cooling channels are to be embedded when the glass material is deposited, the deposition process can be stopped and the spacers can, if necessary, be placed directly on the glass material that has already solidified. The deposition process is then continued in order to embed the placeholders in the glass material. Alternatively, the quartz glass material or the glass ceramic produced by direct deposition or in a soot process can be divided into two or possibly more sub-bodies in order to form the cooling channels in or between the sub-bodies, which are subsequently (re) joined or respectively by means of high-temperature bonding be connected to each other.

In a further variant, the method additionally comprises: producing a substrate for an optical element by, in particular, mechanical processing of the glass body. As a rule, the glass body is mechanically (finished) processed in order to produce the desired shape of the substrate. For example, the substrate can be cut from the glass body by severing an edge region of the glass body, e.g. is cut off or milled off. The area in which a reflective coating is to be applied to the substrate is usually polished before the coating is applied in order to produce a low surface roughness.

Another aspect of the invention relates to a reflective optical element, in particular for reflecting EUV radiation, comprising: a substrate which has at least one cooling channel and which is produced according to the method described above, and a reflective coating applied to the substrate. The reflective coating can in particular be designed to reflect EUV radiation at a wavelength between approx. 5 nm and approx. 30 nm. The specific design of such a reflective coating is familiar to the person skilled in the art, so that it is not described in more detail in the present application. In such an optical element, in which the cooling channel was produced using a placeholder, small remnants of the spacer and / or an impression of the spacer typically remain in the respective cooling channel, which allow conclusions to be drawn about the manufacture of the optical element or the respective placeholder used . The same applies to the mechanical processing, e.g. by milling, introduced cooling channels, as well as for bonding planes, which are also detectable on the substrate or the optical element.

Another aspect of the invention relates to an optical arrangement, in particular an EUV lithography system, comprising: at least one reflective optical element, which is designed as described above, and a cooling device, which is designed to allow a cooling liquid to flow through the at least one cooling channel. The EUV lithography system can be an EUV lithography system for exposing a wafer or another optical arrangement that uses EUV radiation, for example an EUV inspection system, e.g. for the inspection of masks, wafers or the like used in EUV lithography. The reflective optical element can in particular be a mirror of a projection system of an EUV lithography system. The cooling device can be designed, for example, to allow a cooling liquid in the form of cooling water or the like to flow through the through channel. For this purpose, the cooling device can optionally have a pump and suitable supply and discharge lines.

It goes without saying that the glass body can in principle also be used for purposes other than producing a (reflective) optical element. In this case, too, the cooling channel or channels can be used to cool the glass body can be used if a cooling fluid, for example cooling water, flows through it.

Further features and advantages of the invention emerge from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing which show details essential to the invention, and from the claims. The individual features can each be implemented individually or collectively in any combination in a variant of the invention.

Figure list

• 1a,b schematische Darstellungen eines ersten Teilkörpers eines Glaskörpers, in den Kühlkanäle eingefräst sind, und eines zweiten Teilkörpers des Glaskörpers,
• 2a,b schematische Darstellungen analog zu 1a,b, bei denen drei unterschiedliche Arten von Platzhaltern in die Kühlkanäle eingebracht sind,
• 3a,b Darstellungen analog zu 1a,b, bei denen die Platzhalter beim Hochtemperatur-Bonden zwischen die beiden Teilkörper eingebettet werden,
• 4a,b zwei Darstellungen eines Trägers, auf den ein Glasmaterial abgeschieden wird, beim Einlegen von Platzhaltern sowie beim Einbetten der Platzhalter in das Glasmaterial,
• 5a-c Darstellungen eines Platzhalters mit einem massiven Grundkörper, an dessen Umfang Lamellen gebildet sind bzw. der in eine Schicht aus einem Granulat eingebettet ist, sowie
• 6a-d Darstellungen eines rohrförmigen Platzhalters, an dessen Umfang voneinander beabstandete Schlitze gebildet sind bzw. der als Spiralrohr ausgebildet ist.

Exemplary embodiments are shown in the schematic drawing and are explained in the following description. It shows

• 1a, b schematic representations of a first part of a glass body in which cooling channels are milled, and of a second part of the glass body,
• 2a, b schematic representations analogous to 1a, b , in which three different types of placeholders are inserted in the cooling channels,
• 3a, b Representations analogous to 1a, b , in which the placeholders are embedded between the two partial bodies during high-temperature bonding,
• 4a, b two representations of a carrier on which a glass material is deposited, when inserting placeholders and when embedding the placeholders in the glass material,
• 5a-c Representations of a placeholder with a solid base body, on the circumference of which lamellae are formed or which is embedded in a layer of granules, and
• 6a-d Representations of a tubular placeholder, on the circumference of which slots spaced apart from one another are formed or which is designed as a spiral tube.

In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

1 a, b show an example of a method for manufacturing a glass body 1 , of a plurality of cooling channels 2 having. In the process, a first, lower part of the body 3a and a second, upper part of the body 3b one in 1b illustrated, substantially cylindrical glass body 1 provided. In the example shown, the lower part of the body 3a of the vitreous 1 , more precisely its glass material 4th mechanically on a surface 5a machined by putting in the glass material 4th a plurality of cooling channels 2 is milled.

The two part bodies 3a , b will be on the machined surface 5a connected to one another by the second partial body 3b with a non-machined surface 5b on the first part of the body 3a is placed and both part of the body 3a , b are jointly subjected to a high-temperature bonding process. In the case of high-temperature bonding, the two part bodies are 3a , b heated to temperatures of over 1000 ° C, usually between approx. 1300 ° C or 1500 ° C and 2000 ° C, the two surfaces in contact with one another 5a , b are usually fused to one another, so that there is a permanent connection between the two partial bodies 3a , b trains.

The two part bodies 3a , b are provided by the massive glass body 1 (without cooling channels) is sawed along a curved parting surface in the example shown by means of spherical cutting loops, with the surfaces, which are also curved 5a , b train. The two surfaces 5a , b, on which the partial bodies 3a , b are connected to one another, are therefore precisely matched to one another. Sawing open the glass body 1 along a curved separation surface is advantageous to a constant distance between the cooling channels 2 and a likewise curved optical surface or mirror surface 6th to generate the in 1a is shown in dashed lines. The mirror surface 6th is produced by mechanical processing, for example by milling or the like, in which the glass body 1 a mirror substrate is produced with a desired geometry. During the mechanical processing to manufacture the mirror substrate, the glass body 1 usually also trimmed at the edges.

To produce a reflective optical element, the mirror surface is applied 6th the substrate or the mechanically processed glass body 1 is applied a reflective coating. In the example shown, where the glass body 1 is used to produce an EUV mirror, the reflective coating is designed to reflect EUV radiation at an operating wavelength in the EUV wavelength range between approx. 5 nm and approx. 30 nm and for this purpose has a plurality of alternating layers from a high refractive and a low refractive material.

To ensure sufficient dimensional stability of the glass body 1 and unwanted geometry deviations from the glass body 1 To ensure produced mirror substrate, it is necessary that in particular that with the cooling channels 2 provided lower body parts 3a during the High temperature bonding remains dimensionally stable. To achieve this without placing placeholders in the cooling channels for the high-temperature bonding 2 are introduced, compliance with specified geometry parameters is favorable or necessary, as below with reference to 1a is described.

The in 1a The example shown are the cooling channels 2 introduced parallel to each other along an X direction of an XYZ coordinate system, which is the main direction or the longitudinal direction of the cooling channels 2 forms. The cooling channels 2 each have a width B in the range between approx. 0.5 mm and 3.0 mm in the example shown. As in 1a can also be seen, during mechanical processing between two adjacent cooling channels 2 Bridges 7th in the glass material 4th of the lower part of the body 3a educated. The web width A of the webs 7th in the Y direction, which corresponds to the distance A between two adjacent cooling channels 2 in the Y-direction is more than 10 times, possibly more than 20 times, more than 50 times or even more than 100 times the width B of a respective cooling channel 2 , ie the following applies: A / B> 10 or>20,> 50 or> 100. It should be noted that 1a is not to scale to simplify the illustration.

The relatively small proportion of the width B of the cooling channels 2 along the entire width of the vitreous 2 in the Y-direction ensures that the webs 7th stop during bonding and do not bend or tip over under the influence of gravity. To ensure a sufficient flow of cooling liquid through the cooling channels despite the large A / B ratio 2 to ensure it is favorable if the depth C of the cooling channels 2 is chosen to be comparatively large in the Z direction. For the depth C of the cooling channels 2 should apply: 20 B>C> 2 B.

In particular in the event that the channel portion is comparatively large, ie in the event that A / B <20, or in the event that the cooling channels are comparatively high (B / C <5), it can be advantageous to have at least two channel-free areas in the lower part of the body 3a train, for whose width D applies: D> 3 C and / or D> 5 A. In 1a are examples of two channel-free areas 8a , b shown, which on the two side edges of the lower part of the body 3a are formed.

In 2a, b is an example of the manufacture of a glass body 1 analogous to the in 1a, b shown example, in which before connecting the two part bodies 3a , b a placeholder in each case through high-temperature bonding 9a-c in a respective cooling channel 2 is introduced. In 2a, b are three examples of different placeholders to simplify the illustration 9a-c shown, each in a cooling channel 2 are arranged. Usually used in the manufacture of a vitreous 1 just a single type of placeholder 9a-c used.

In 2a on the left is a placeholder 9a formed from a granulate or from a granular material that is not dimensionally stable. The granulate is a sand, optionally graded in grain size, made of a temperature-resistant material, for example an oxide ceramic or a nitride, which is fed into the milled-out cooling channel 2 was pressed. In the in 2a cooling channel shown in the middle 2 is a massive, wire-like placeholder 9b introduced, while in the in 2a cooling channel shown on the right 2 a tubular placeholder 9c is introduced.

So that the respective placeholder 9a-c when high-temperature bonding maintains its dimensional stability, it is necessary that the temperature-resistant material of the placeholder 9a-c has a comparatively high melting point of more than approx. 1500 ° C, of more than approx. 2000 ° C, ideally of more than approx. 3000 ° C. The temperature-resistant material can be formed from different materials, for example from metals or semi-metals, from carbon, .... Materials that have a melting point of more than approx. 1500 ° C. and which are therefore suitable as temperature-resistant materials for the placeholder are, for example, Ti, Pa, Pt, Zr, Cr, V, Rh, Hf, Tc, Ru, B , Ir, Nb, Mo, Ta, Os, Re, W, C.

As in 2 B can be seen, the in 2a Placeholders shown on the left and in the middle 9a , b after connecting the two partial bodies 3a , b from the respective cooling channel 2 removed, while the tubular placeholder shown on the right 9c after manufacturing the vitreous 1 in the cooling channel 2 remains. The in 2 B cooling channel shown on the right 2 the cooling liquid will therefore pass through the cavity in the tubular placeholder 9c guided. The in 2a The placeholder shown on the left is made from the granulate after the glass body has cooled down 1 by means of a water jet nozzle and possibly using a wire from the cooling duct 2 away. The in 2a massive placeholders shown in the middle 9b becomes from the cooling duct 2 away. The massive placeholder 9b is made of a temperature-resistant but flammable material, more precisely carbon, and can therefore be burned off with the supply of an oxidizing gas in the form of oxygen from the cooling channel 2 removed. In order to avoid that the glass material 4th Heated locally to more than 600 ° C, the supply of oxygen in the cooling channel 2 by inserting a probe indicated by dashed lines 11 limited. In addition to carbon, most of the materials listed above are also flammable and can, if necessary, be removed from the respective cooling duct by means of controlled burning. To avoid burning off the not refractory placeholder 9b occurs in an uncontrolled manner during the high-temperature bonding, the high-temperature bonding is carried out under protective gas or in a protective gas atmosphere.

3a, b show two partial bodies 3a , b made of glass material 4th that like in 1a, b be connected to each other by high temperature bonding. For this purpose, as in 1a, b the upper part of the body 3b on the lower part of the body 3a hung up. Unlike in 1a, b become the cooling channels 2 but not by milling one or both part bodies 3a , b manufactured. Rather, there will be a plurality of placeholders 9d on top 5a of the lower part of the body 3a placed in the glass material during high-temperature bonding 4th of the vitreous 1 be embedded. This in 3a, b The procedure shown is particularly favorable in the event that the placeholders 9b have a certain robustness because they are formed from a metal, for example. As described above, most metallic materials have the problem that they burn at high temperatures in contact with oxygen from the environment.

In order not to have to carry out the high-temperature bonding under a protective gas atmosphere, the in 3a, b shown placeholder 9 made of a solid, flammable material, for example tungsten or graphite, an inert, fire-resistant coating 12 applied from platinum. Other non-flammable materials, for example osmium, are also suitable as materials for a (fire-resistant) coating that is inert to oxidation.

In the event that as in 3a, b a massive and not a tubular placeholder 9d is used, it must be used to form the cooling channels from the glass material 4th of the vitreous 1 removed. The metallic material or graphite can be removed by burning off, as described above. Alternatively, it is when using a placeholder 9d from a metallic material possible to remove this electrochemically. Chemical removal of the material by an etching treatment is also possible, the type of etchant depending on the type of metallic material. For example, tungsten can be dissolved in a mixture of sodium nitrate and sodium carbonate or similar alkali salts heated to a temperature of approx. 400 ° C-600 ° C. A placeholder 9d For example, titanium can be dissolved in concentrated sulfuric acid, which is the glass material 4th does not attack.

4a, b show another way of embedding placeholders 9e into the glass material 4th of the vitreous 1 in which the embedding during the deposition of glass material 4th takes place on a carrier, which is designed in the form of a container in the example shown, but which can also be designed as a turntable or the like. In the example shown, it is the glass material 4th titanium-doped quartz glass (ULE®), which is produced by direct deposition, as is the case, for example, in the U.S. 5,970,751 is described. The glass material is on the carrier 13 deposited until this has reached a predetermined height. In a subsequent step, the placeholders 9e on the already deposited, solidified glass material 4th placed, these possibly being stabilized by means of a network of cross-connectors, not shown in the figure.

The following is the deposition of the quartz glass material 4th continued until the desired height of the vitreous 1 is achieved. After the vitreous 1 has cooled below its solidification temperature in its entire volume, this is typically removed from the carrier for further processing 13 or removed from the container. Instead of the procedure described here, in which to insert the placeholder 9e the deposition process has to be interrupted, it is alternatively possible to use the placeholders 9e suitable to fix in the container before the start of the deposition process. In this way, the process of depositing the glass material 4th can be carried out without interruption.

The in 4a, b The example shown is the placeholder 9e around a body 14th from a mixture containing sand held together with a binding agent. Alternatively, it can be the placeholder 9e around a porous or granular body 14th act from a roughly sintered or pressed material. For making such a body 14th In particular, non-combustible materials such as oxides, especially oxide ceramics, or nitrides, such as boron nitride or titanium nitride, are suitable. In the case of such materials, the application of a refractory coating can be dispensed with.

Used as a placeholder 9e a body 14th If a CaO or MgO ceramic is used, there is the problem that these materials may be mixed with the glass material 4th of the vitreous 1 react so that this undesirable way in the glass material 4th be integrated. To prevent this, the in 4a, b example shown on the body 14th one against a reaction with the glass material 4th of the vitreous 1 inert coating 15th upset. The coating 15th is made of platinum in the example shown, which wets the glass surface and prevents further reactions. As described above, platinum does not react with atmospheric oxygen even at high temperatures and is therefore also suitable as a refractory coating 12 .

Are nitrides, e.g. boron nitride or titanium nitride, used to make the placeholder 9e or the body 14th Used can usually be due to the application of a counteracting reaction with the glass material 4th inert coating can be dispensed with, since these materials are already chemically inert to such a reaction. In the event that as in 1a, b the cooling channels are shown 2 by mechanical processing into the glass material 4th can be introduced against the reaction with the glass material 4th inert coating 15th on the wall of the cooling channel 2 be applied.

The porous or pressed bodies described above 14th can usually be dissolved by a water jet or by an ultrasound treatment and so out of the cooling channels 2 removed. CaO as oxide ceramic has the advantage that it has a high melting temperature of approx. 2580 ° C, but CaO reacts strongly exothermically with water. Hence, it is beneficial to keep the CaO level in the body 14th not too big to choose. This is possible, for example, when the body 14th as described above, a mixture of sand, for example aluminum oxide or boron nitride, is formed with CaO as a binder. Such a body 14th can by adding water or a water jet from the glass body 1 be removed, as the heat development can be controlled. For making such a body 14th another type of binder, e.g. MgO, can also be used. MgO reacts only comparatively weakly with water. However, this reaction can be sufficient to reduce the strength of a comparatively weakly bound mixture to such an extent that it can easily be removed from the glass body 1 can be removed.

Most of the temperature-resistant materials described above have a higher thermal expansion than the glass material 4th of the vitreous 1 . When cooling the vitreous 1 after that in connection with 1a, b and 3a, b described bonding process or after in connection with 4a, b described glass deposition process pull the placeholders 9a-e therefore typically stronger together than the glass material 1 and in the process detach themselves from the glass material over large parts of their circumference in an uncontrolled manner 1 from. In principle, this simplifies the removal of the placeholders 9a-e after cooling, before peeling off, practice the placeholders 9a-e however, tensile stresses on the glass material 4th some of which can no longer relax before solidifying and are frozen. The following are several examples of placeholders 9b , 9c described, which allow the tensile stresses to be reduced when the glass body cools down.

In the 5a-c shown placeholder 9b each have a massive body 16 which is formed in the example shown from a metallic material. The in 5a shown placeholder 9b is a number of four T-shaped slats 17th along the perimeter 16a of the placeholder 9b distributed. The slats 17th are each by column 18th separated from each other, which have a gap width s in the circumferential direction between approximately 0.5 mm and 3.0 mm. The slats 17th remain with the exertion of a low tensile force on a large part of their surface with the glass material 4th remain connected and only loosen via their web-shaped connection to the solid base body 16 from. 5b shows a placeholder 9b with a massive body 16 analogous to 5a , along its perimeter 16a a number of eight L-shaped slats 17th is formed. The slats 17th are made by inserting into the base body 16 Millings can be made with the desired geometry.

The in 5c The example shown is the massive body 16 of the placeholder 9b in one shift 19th embedded when contracting the placeholder 9b lower tensile stress on the glass material during cooling 4th exercises than the massive base body 16 . The layer 19th into which the base body 16 is embedded, can for example be formed from granules / sand, which is optionally connected with a binding agent, or from a solid foam.

6a-d show examples of tubular placeholders 9c , which also apply to the glass material when it cools down 4th applied tensile stress can be reduced. In the in 6a, b tubular placeholder shown 9c are longitudinal slots 20th introduced, which are arranged offset to one another in the circumferential direction. As in 6a can be seen are the slots 20th preferably uniformly in the circumferential direction along the placeholder 9c arranged distributed. To avoid tension in the longitudinal direction of the placeholder 9c build up are the slots 20th at the in 6c shown example slightly coiled. 6d shows a placeholder 9c that is in the form of a spiral tube 21st is trained.

When introducing placeholders 9a-c into the cooling channels formed by mechanical processing 2 from 2a, b the problem is that the placeholders 9a-c in the case of high-temperature bonding, they usually expand more than the glass material 4th of the vitreous 1 . About the introduction of stresses into the glass material 4th to avoid when heating, the in 2a, b placeholders shown in the middle 9b possibly dimensioned smaller than the corresponding cooling channel 2

As described above, the one with cooling channels 2 provided glass body 1 a mechanical finishing carried out to to manufacture or shape a substrate for a reflective optical element. During the mechanical processing to produce the substrate, a peripheral edge of the glass body is typically used 1 cut off as well as the in 1a optical surface shown in dashed lines 6th educated. In addition, the (in 1a concave curved) surface 6th , to which a reflective coating is applied, polished to reduce surface roughness. The reflective coating can be designed, for example, to reflect radiation at an operating wavelength in the EUV wavelength range between approx. 5 nm and approx. 30 nm.

Such a reflective optical element or such a mirror for reflecting EUV radiation can be arranged in an EUV lithography system, for example in an EUV lithography system. Such an EUV lithography system in this case has a cooling device which makes it possible to use the at least one cooling channel 2 to flow through in the substrate with a cooling fluid, in particular with cooling water. The cooling device can have corresponding connections and lines for supplying or discharging the cooling fluid into or from the respective cooling channels 2 exhibit. The cooling device can have a pump or the like in order to circulate the cooling fluid. However, it is also possible for the cooling device to be connected to a cooling water supply via a cooling water connection. It goes without saying that the use of the glass body 1 with the cooling channels 2 is not limited to EUV lithography, but that of the glass body 1 or a substrate formed from this can also be used in other optical arrangements.

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102017221388 A1 [0004]
• WO 2012/126830 A1 [0005]
• US 7591561 B2 [0006]
• US 5970751 f [0018]
• US 5970751 [0036, 0059]

Claims (27)

A method for producing a glass body (1) with at least one cooling channel, preferably with a plurality of cooling channels (2), comprising: Providing a first part-body (3a) and a second part-body (3b) of the glass body (1), Forming at least one cooling channel (2) by in particular mechanical processing of the glass material (4) on a surface (5a) of the first part body (3a) and / or the second part body (3b), and Manufacture of the glass body (1) by connecting the first part body (3a) to the second part body (3b) on the machined surface (5a) by high temperature bonding. Procedure according to Claim 1 , in which cooling channels (2) separated from one another by webs (7) are formed during processing of the glass material (4), the web width A of which in the lateral direction (Y) is at least 10 times, preferably at least 20 times, particularly preferably at least 50 times, in particular at least 100 times the width B of a respective cooling channel (2). Procedure according to Claim 1 or 2 , in which the cooling channels (2) are formed with a depth C which is between 2 times and 20 times the width B of a respective cooling channel (2) during machining. Method according to one of the preceding claims, in which the provision comprises dividing the glass body (1) into the first part body (3a) and into the second part body (3b) along an in particular curved surface (5a, b). Method according to one of the preceding claims, in which a placeholder (9a-e) made of a temperature-resistant material (10) is introduced into the cooling channel (2) before the two partial bodies (3a, b) are connected. A method for producing a glass body (1) with at least one cooling channel, preferably with a plurality of cooling channels (2), comprising: Embed at least one placeholder (9a-e) made of a temperature-resistant material (10) in the glass material (4) of the glass body (1) during the manufacture of the glass body (1) to form the at least one cooling channel (2) in the glass body (1) . Procedure according to Claim 6 , further comprising: providing a first part body (3a) and a second part body (3b) of the glass body (1), as well as producing the glass body (1) by connecting the first part body (3a) to the second part body (3b) by high-temperature bonding while embedding the at least one placeholder (9d) between the two partial bodies (3a, b). Procedure according to Claim 6 , further comprising: depositing glass material (4) on a carrier (13), embedding the placeholder (9e) in the deposited glass material (4), and cooling the glass material (4) to produce the glass body (1). Method according to one of the Claims 5 to 8th , in which the placeholder (9c) is tubular and remains in the cooling channel (2) after the glass body (1) has been produced. Method according to one of the Claims 5 to 9 , in which the placeholder (9a, b; 9d, 9e) is removed from the glass body (1) after the production of the glass body (1) to form the cooling channel (2). Procedure according to Claim 10 , in which the placeholder (9b) has a base body (16) on the circumference of which there are formed lamellae (17) which run in the longitudinal direction and are separated from one another by gaps (18). Procedure according to Claim 10 , in which the placeholder (9c) is tubular and either has slots (20) spaced from one another or is designed as a spiral tube (21). Procedure according to Claim 10 , in which the placeholder (9b) has a base body (16) which is embedded in a layer (19) made of granules and / or of a solid foam. Method according to one of the Claims 5 to 13 , in which the temperature-resistant material (10) of the placeholder (9a-e) has a melting point of more than 1500 ° C, preferably more than 2000 ° C, in particular more than 3000 ° C and preferably made of a metallic material or a semi-metal is formed. Method according to one of the Claims 5 to 14th , in which the temperature-resistant material of the placeholder (9a-e) is selected from the group comprising: Ti, Pa, Pt, Zr, Cr, V, Rh, Hf, Tc, Ru, B, Ir, Nb, Mo, Ta, Os, Re, W, C. Method according to one of the Claims 5 to 15th , during the manufacture of the glass body (1) takes place under protective gas. Method according to one of the Claims 5 to 16 , in which the placeholder (9e) contains a non-combustible material, preferably an oxide, in particular an oxide ceramic, or a nitride, or in which the placeholder (9e) is formed from the non-combustible material. Method according to one of the Claims 5 to 17th , in which a coating (12) inert to oxidation is applied to the placeholder (9d). Method according to one of the Claims 5 to 18th In which a coating (15) which is inert to a reaction with the glass material (4) of the glass body (1) is applied to the placeholder (9e) or to a wall of the cooling channel (2). Method according to one of the Claims 5 to 8th or 10 to 19th , in which the placeholder (9e) is a pressed or sintered body (14) or a body (14) formed from a mixture connected with a binding agent. Method according to one of the Claims 5 to 19th in which the placeholder (9a) is formed from granules. Method according to one of the Claims 10 to 20th , in which the removal of the placeholder (9b) takes place by burning off the placeholder (9b) while supplying an oxidizing gas. Method according to one of the Claims 10 to 21st , in which the preferably metallic placeholder (9d) is removed by electrochemical removal and / or by an etching treatment. Method according to one of the preceding claims, in which the glass material (4) of the glass body (1) is formed from quartz glass, preferably from titanium-doped quartz glass. A method according to any one of the preceding claims, further comprising: Production of a substrate for an optical element by, in particular, mechanical processing of the glass body (1). Reflective optical element, in particular for reflecting EUV radiation, comprising: a substrate which has at least one cooling channel (2) and according to the method according to Claim 25 is produced, as well as a reflective coating applied to the substrate. Optical arrangement, in particular EUV lithography system, comprising: at least one optical element according to Claim 26 , as well as a cooling device which is designed for a cooling liquid to flow through the at least one cooling channel (2).

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