DE102008011354B3 - Method for joining two components to a composite structure by "fusion bonding" and composite structure, optical element, holding device, projection lens and projection exposure apparatus produced thereby - Google Patents

Abstract

The invention relates to a method for joining at least one first and one second component (1, 2) to a composite structure (6) by fusion bonding, comprising the steps of: a) applying at least one layer (3, 4) of porous structure b) roughening the at least one applied layer (3, 4), c) merging the surface (1a) of the first component (1) with a surface (2a) the second component (2); and d) bonding the components (1, 2) to the composite structure (6) by fusion bonding. The invention further relates to a composite structure (6), an optical element and a holding device for a wafer, which are manufactured from such a composite structure, as well as a projection objective and a projection exposure apparatus with such an optical element.

Description

State of the art

The The invention relates to a method for connecting at least one first and a second component to a composite structure by "fusion bonding", a Composite structure, an optical element and a holding device for one Wafers, which are made of such a composite structure, as well as a projection lens and a projection exposure system with such an optical element.

at the production of optical elements, eg. As lenses or phase shifters, and in the manufacture of mechanical elements such as wafer holding devices it is often desirable Components with possibly different optical or mechanical Properties to connect to a composite structure. This is It is known to use so-called bonding methods, such as Example low temperature ("low temperature ") - bonding, usually at Room temperature or slightly higher Temperature performed is and in which between the components to be assembled in the Usually liquid joining means is introduced, which is subsequently cured. Next to it will be too the so-called direct bonding ("fusion bonding ") used in which the materials of the components are compressed and typically heated to just below the transition temperature be around this at a joint to connect with each other, without this being an additional joining means requirement. The composite structure is subsequently usually mechanical edited to obtain an optical element with the desired shape. At the End of this process, chew an item out of a material, that does not occur in nature.

An example of such an optical element is the terminating lens of a projection lens for microlithography, which is z. B. from several lens shells of a crystalline material, for. B. Lutetium aluminum garnet (LuAG, Lu ₃ Al ₅ O ₁₂ ), which are each arranged at a predetermined angle to each other twisted to compensate for the natural birefringence in the material.

In addition, it is z. B. from the WO 2006/061225 A1 bekamt used to use polycrystalline materials having a grain size above the wavelength of the radiation used as a final element of a projection lens. In some of the materials described there such. B. polycrystalline spinel (MgAl ₂ O ₄ ), the problem arises that can be made of these materials components only up to a maximum thickness of about 40 mm. Since the terminating lens is usually much thicker, several such spinel components must be arranged one above the other and preferably joined together by means of "fusion bonding".

In microlithography, in addition to holding a wafer, mechanical devices (wafer chuck, wafer stage, wafer table) are required which, although partly monolithically realizable, are generally relatively heavy due to the required sizes. In such applications, therefore, a composite structure is often desired in which voids are formed to reduce the weight between the assembled components. Furthermore, it may be necessary to use in one part of the holding device a material with high hardness and thus high density, the use of which is not required in another part of the composite structure, so that there can be used for weight reduction, a lower density material, if the Holding device is realized as a composite structure. In general, in this case materials are connected to each other, which have a similar coefficient of thermal expansion (CTE), as in the WO 2008/17449 A2 the applicant, which is incorporated by reference in its entirety to the content of this application.

For "fusion bonding", the surfaces to be joined together are usually prepared by peeling them together. Wringing is a combination of two materials in which surfaces are held only by molecular attractive forces, ie it is a "releasable" compound which can be partially or completely dissolved (under the influence of moisture or wedge action). For wringing, however, the components to be joined must be free of particles, which is achieved by surface cleaning, and polished to a near perfect surface flatness. In the case of the above-described optical element as for the holding device usually required diameters of about 200 mm, corresponding to an area of about 400 cm ² , but the problem arises that conventional cleaning methods such as cleaning with acetone or rubbing with deerskin although they can be carried out, yet the surfaces do not adhere to each other, since the adhesion depends on the absolute number of contaminant particles present on the surfaces, which increases with the size of the surface, even when cleaning is performed. Without such a cleaning step, however, large-area wringing is generally not possible, which is why "fusion bonding" did not occur on large surfaces or only with poor results.

From the US 2005/0215028 A1 is a procedure ren known in which an amorphous and non-hydrogenated intermediate layer applied to one of two components to be joined and the two components are arranged spaced apart by the intermediate layer. One or both components are heated before they are brought into contact with each other. Subsequently, a voltage is applied to maintain a permanent connection between the two components.

The US 2003/0211705 A1 describes a low-temperature bonding method in which the surfaces of the components to be joined are made of materials such as silicon, silicon nitride or silicon oxide before bonding at room temperature, ie pretreated by cleaning or etching. For this purpose, so-called "very slight etch" methods can be used in which the microroughness of the surfaces is largely retained, or reactive ion etching or plasma etching can be used.

Under the web address "www.heise.de/newsticker/meldung/76740" is a so-called Velcro closure to produce a detachable connection of Semiconductor chips have become known in which the surface of a Silicon device z. B. roughened by ion bombardment and thereby a fine structure of silicon needles is generated. Through the velcro intended to heat the components to produce a solid Connection can be dispensed with.

Other records of direct bonding are known from DE 38 29 906 A1 . WO 03/02597 A1 and US 2009/0035443 A1 ,

Object of the invention

task It is the object of the invention to provide a method for connecting two components, which direct bonding ("fusion bonding ") also great zusammenzufügender surface areas allows one Composite structure, an optical element and a support structure for one Wafer made of the composite structure, a projection lens and a projection exposure apparatus with such an optical Provide element.

Subject of the invention

These Task is done according to a solved first aspect of the invention by a method of the type mentioned above, comprising the steps: a) applying at least one layer of porous structure to a surface of each b) roughening the at least one applied layer, c) Merge the surface the first component having a surface of the second component, and d) joining the components to the composite structure by fusion bonding ". The inventors have recognized that the usual way of "fusion bonding "preliminary Wringing can be replaced by two surfaces facing each other be laid, of which at least one is roughened, which also leads to a fixation of the two surfaces relative to each other (see Velcro), so that in a subsequent step, the "fusion bonding" can be performed.

in this connection is added to the material of the first component an additional, usually polycrystalline layer applied, which is a porous structure has, so that it can be easily roughened. usual The way to the other components to be connected also such a layer applied to a good fixation of the surfaces together to enable. However, it is alternatively possible, if possible, only the first component to be provided with such a layer.

Preferably, materials having the same chemical composition are selected for the component and the layer applied thereto. Materials with the same chemical composition are materials whose structure (geometric structure) may be different, but whose chemical structural formula is identical. In particular, z. Example, a layer on a component of spinel (MgAl ₂ O ₄ ) by co-coating of MgO and Al ₂ O ₃ in the ratio 1: 1 are generated. In this case, the geometric structure of the layer differs from the spinel structure, but the material of the layer and the component have the same chemical structural formula, yet a good adhesion of the layer to the component is ensured.

at an advantageous embodiment is for the components to be connected selected the same material. This Material preferably matches the material of the layer (s). In the above example, after the fusion bonding of the spinel layer with two components of spinel a composite structure of one single material, which is essentially optically homogeneous, because the "fusion bonding "the porous Layer converted into a compact spinel layer.

In a preferred variant, the material is selected from the group comprising: spinel (MgAl ₂ O ₄ ), alumina (Al ₂ O ₃ ) and LuAG (Lu ₃ Al ₅ O ₁₂ ), cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ) , Silicon carbide (SiC), (quartz) glass and glass ceramic, in particular Zerodur, ULE or Clearceram. In particular, spinel and alumina, in addition to LuAG due to their high refractive index suitable materials for a final element of a projection lens for Microlithography. Due to the size of the terminating lens - depending on the selected material - this may not be made from a single component. When bonding the in such a closure element usually large-scale surfaces to be joined, the problem arises that they can not be cleaned sufficiently well to allow wringing. It goes without saying that, in addition to the abovementioned materials which are transparent to UV radiation, it is also possible to use other materials which are transparent to UV radiation, in particular when used as the terminating element of a projection objective for microlithography at a wavelength of 193 nm should have a refractive index greater than quartz glass. However, non-transparent materials such as cordierite or silicon carbide are also suitable materials for the components of the composite structure, in particular if this is to be used as a holding device for a wafer.

at In a further variant, the layer is applied by means of a Method selected from the group comprising: Physical Vapor Deposition (PVD, physical Vapor deposition), in particular thermal evaporation, electron beam evaporation, Sputtering (Cathodic Sputtering), Ionized Cluster Beam Deposition (ICVD, Cluster Beam Technology) and Chemical Vapor Deposition (CVD, chemical vapor deposition). The mentioned Methods relate to techniques for coating substrates by Vapor deposition, wherein between physical vapor deposition, in which no chemical reaction takes place during vapor deposition, and chemical vapor deposition with such a chemical reaction a distinction is made. It is understood that also variants of said methods can be used z. B. magnetron sputtering, in which a low-temperature plasma in a Noble gas (usually argon) is used to remove a target material and on one opposite deposition of substrate or ion beam sputtering for which purpose an ion beam is used. The coating must be different than usual not necessarily done under vacuum, since the layer should be porous. to Production of such a porous Layer is particularly suitable for atmospheric pressure CVD.

at In a particularly advantageous variant, the application of the layer at a coating temperature of less than 1000 ° C, preferably from less than 300 ° C carried out. In this way it can be achieved that porous, polycrystalline layers arise, what for the later one Roughing is beneficial.

at In a particularly advantageous variant, the surfaces of the Components for applying the layer with a surface roughness of 1.0 nm rms or less and preferably a surface flatness of less than λ, in particular less than λ / 2 at λ = 632 now provided. As a result, the subsequent application the layer are facilitated. If the composite structure as optical Element is to be used, it is particularly advantageous if the surface roughness at λ or below where λ is the Measuring wavelength of 632 nm (He-Ne laser).

at In another preferred variant, the surface is present the coating is cleaned and degreased, thereby applying a layer with for the bonding particularly advantageous properties are facilitated can.

Prefers the coating is applied by co-coating at least two constituents of the material. As already mentioned above with the example of Spinel, can / can the layer (s) are applied by two or more their constituents are vaporized in such a ratio that the chemical composition of the desired layer material sets.

In In an advantageous variant, the layer with a thickness of 500 nm or less, preferably 100 nm or less. By applying a thin This layer can be relatively efficient in subsequent annealing during fusion bonding be converted into a compact material layer, so that the process can be carried out at low process duration.

Prefers roughening is carried out by means of a procedure that selected is from the group comprising: dry etching, wet etching and Ion beam bombardment. The surfaces are roughened in all processes only so far that they themselves during the subsequent "fusion bonding "not can move relative to each other. By roughening this is a layer with a columnar, the above mentioned Velcro generated related structure.

In a particularly advantageous variant, the surfaces after merging fixed at a static pressure of more than 1 bar, which is for the subsequent "fusion bonding "is favorable.

Advantageously, the fusion bonding takes place at a temperature of at most 2100 ° C., preferably 1500 ° C., more preferably of at most 1300 ° C. By not too high a temperature during the bonding can be achieved that deformations by the increase of the viscosity in the proximity of the Transition temperature as low as possible. The temperature during bonding can be chosen so high; that a melting of the surfaces takes place, ie it can, for. In the case of spinel, for example, a temperature of about 2100 ° C. or, in the case of aluminum oxide, a temperature of about 2000 ° C. can be achieved. The "fusion bonding" is in this case preferably under a process gas such. As argon or oxygen carried out.

In In an advantageous variant, the fusion bonding takes place in one Temperature of 70% or less, preferably 60% or less the melting temperature of the layer. In this case, the "fusion bonding "through hidden diffusion or migration, so that no melting of the to be joined surfaces necessary is.

Around but to create the hidden diffusion usually has one Temperature can be achieved, at least at more than 50% of the melting temperature the layer lies. It is understood that when connecting two Layers of different layer materials the melting temperature the layer with the higher Melting point is the relevant melting temperature.

One second aspect of the invention is realized in a composite structure, in particular produced according to the method as described above, with at least a first and second component of the same Material attached to two surfaces connected to each other, wherein between the surfaces of a Intermediate layer is introduced, which by "fusion bonding" of the components with at least one applied to a surface of each of the components, roughened layer with porous structure is formed. Here are the component and the on this applied layer preferably of materials with the same chemical Composition. In particular, the components also consist of the same material, so in the case of transparent to UV radiation Components are obtained an optically homogeneous composite structure came.

A Composite structure in which multiple components to those described above Way over each other can be arranged to form an optical element, for. B. a final element of a projection lens for microlithography used become. Alternatively, from such a composite structure and a Holding device for a wafer, in particular a wafer chuck or a wafer table, getting produced.

In a particularly advantageous embodiment, the intermediate layer extends over an area of at least 100 cm ² , preferably of at least 400 cm ² . Such large areas are very difficult to connect to each other by wringing, so that the connection in the manner described above is the only way to produce such a composite structure.

In an advantageous variant, the material of the components is polycrystalline. Polycrystalline materials can be used to fabricate optical elements in microlithography as described in the opening paragraph WO 2006/061225 A1 is shown in detail, which is made by reference to the content of this application. In particular, polycrystalline spinel or polycrystalline aluminum oxide can be used for this purpose.

One Another aspect of the invention is realized in an optical Element which is made of a composite structure as above described. The optical element is typically through mechanical processing from the z. B. cylindrical composite structure cut, to the desired Form for to get the particular application.

One Aspect of the invention is realized in a holding device for one Wafer, in particular a wafer chuck or wafer table, made of the composite structure described above is made. In such composed of a plurality of components holding devices can on particularly simple way cavities be formed. Furthermore, can different areas of the holding devices from different, Material types adapted to the requirements of the respective area getting produced.

Yet Another aspect of the invention is realized in a projection lens for the Microlithography for imaging a structure onto a photosensitive Substrate with at least one such optical element, which preferably represents a closure element of the projection lens. such End elements have in particular projection lenses for the Immersion lithography a big one Thickness on to the radiation of the projection lens into the immersion liquid couple. End elements made of materials that are not in the one for this required thickness are available, such as As spinel or alumina, can on the above described Way can be generated from a composite structure.

One aspect of the invention is realized in a projection exposure apparatus for immersion lithography with a projection lens as described above, in which the optical element is disposed opposite to the photosensitive substrate, wherein an immersion liquid is introduced between the photosensitive substrate and the optical element. Like him already In this case, the optical element has a particularly large thickness, so that this is advantageously made of a composite structure.

Further Features and advantages of the invention will become apparent from the following Description of exemplary embodiments the invention, with reference to the figures of the drawing, the invention essential Details show, and from the claims. The individual characteristics can each individually for one or more in any combination in a variant be realized the invention.

drawing

embodiments are shown in the schematic drawing and are in the explained below description. Show it:

1a D is a schematic representation of a plurality of method steps of a variant of the method according to the invention for producing a composite structure,

2 1 is a schematic representation of a projection exposure apparatus with an optical element made of such a composite structure;

3 a schematic representation of a composite structure, which is designed as a wafer chuck (wafer clamping device), and a vacuum source for generating a negative pressure, and

4 a schematic representation of a wafer table as a composite structure with a plurality of interconnected components.

In 1a -D is a schematic of a method for connecting two components 1 . 2 made of polycrystalline material, for. Example of spinel (MgAl ₂ O ₄ ) shown, each having a thickness of about 40 mm. The surfaces 1a . 2a of the components 1 . 2 be at the beginning of the process by means of a suitable smoothing process, for. B. polishing, brought to a surface roughness of less than 1.0 nm rms and a surface flatness of less than λ and degreased and cleaned. On the pretreated surface 1a the first component 1 is in a first step (see. 1a ) by thermal evaporation under vacuum, a layer 3 applied with a thickness of about 100 nm, which also consists of spinel. It is self-evident that other thin-layer methods which are based in particular on the principle of physical or chemical vapor deposition can also be used for coating. Furthermore, instead of spinel as the coating material, it is also possible to use magnesium oxide MgO and aluminum oxide Al ₂ O ₃ , which in a co-coating in a ratio of 1: 1 to the surface 1a be applied. In both cases it forms on the surface 1a a layer 3 from, their chemical composition with that of the component 1 matches. In this case, a coating temperature T _{B is} selected which is less than 300 ° C to a highly porous, polycrystalline structure of the layer 3 to reach.

The porous structure of the layer 3 is in a subsequent step (see. 1b ) exploited these in a simple way on their surface 3a roughen it by using an ion beam 8th is bombarded, leaving a substantially columnar or acicular surface 3a at the shift 3 formed.

The two in 1a , b shown method steps are analogous to the second component 2 performed, whereby at this one in 1c shown, also roughened layer 4 is formed. The two surfaces 1a . 2a of the components 1 . 2 then be like in 1c shown superimposed, with the two layers 3 . 4 adhere to each other, leaving a polycrystalline interlayer 5 formed. The two components 1 . 2 are subsequently subjected to a static pressure of more than 1 bar, before being placed in an in 1d shown, subsequent step by "fusion bonding" are interconnected, ie they are at temperatures of up to max. 2100 ° C under a process gas such. B. argon or oxygen annealed. During annealing, the embedded porous intermediate layer changes 5 from spinel into a compact spinel layer around which the two surfaces 1a . 2a of the components 1 . 2 connects together, leaving a composite structure 6 arises. After cooling the composite structure 6 at room temperature, the connection process is completed. As an alternative to "fusion bonding" by melting, the "fusion bonding" can also be carried out at lower temperatures, typically at about 60% to 70% of the melting temperature of the layers 3 . 4 or the components 1 . 2 in this case, the compound comes about through hidden diffusion.

It is understood that by repeating the method steps described above, several components can be stacked on top of each other so that composite structures of almost any height can be created. Furthermore, the joint, ie the intermediate layer 5 be executed over a large area and in particular cover an area of more than 100 cm ² or 400 cm ² .

In addition to the example shown above, in the spinel as a material of the composite structure 6 or the components 1 . 2 this is the choice Methods are also applied to other materials, eg. Alumina (Al ₂ O ₃ ) or LuAG (Lu ₃ Al ₅ O ₁₂ ), in which case alumina (Al ₂ O ₃ ) or LuAG (Lu ₃ Al ₅ O ₁₂ ) can also be selected as the layer material, to obtain an optically homogeneous composite structure.

The composite structure prepared in the manner described above 6 is particularly suitable in the case that a high refractive index material with a refractive index above quartz glass is selected at a wavelength of 193, for producing an optical element 7 for immersion lithography, as in 2 in a projection exposure machine 10 is shown for the immersion lithography in the form of a wafer scanner for the production of highly integrated semiconductor devices, whose operation is explained below.

The projection exposure machine 10 comprises as light source an excimer laser 11 with a working wavelength of 193 mn, although other working wavelengths, for example 248 nm, are possible. A downstream lighting system 12 produces in its exit plane a large, sharply delimited, very homogeneously illuminated and to the telecentricity requirements of a downstream projection objective 13 adjusted image field.

Behind the lighting system 12 is a facility 14 for holding and manipulating a photomask (not shown) so as to be in the object plane 15 of the projection lens 13 lies and in this plane to scan operation in a by an arrow 16 indicated departure direction is movable.

Behind the level also called mask layer 15 follows the projection lens 13 to form an image of the reduced scale photomask, for example, on a 1: 4 or 1: 5 or 1:10 scale, on a wafer coated with a photoresist layer 17 maps. The serving as a photosensitive substrate wafer 17 is arranged so that the flat substrate surface 18 with the photoresist layer substantially at the image plane 19 of the projection lens 13 coincides. The wafer 17 is through a facility 20 moves, which includes a scanner drive to the wafer 17 synchronously to the photomask and usually in opposite directions to move. The device 20 also includes manipulators to move the wafer both in the z-direction parallel to an optical axis 21 of the projection lens, as well as to move in the x and y direction perpendicular to this axis.

The optical element 7 serves in the projection lens 13 as a final element and is designed as a transparent plano-convex lens, which has a conical lens portion whose end face the last optical surface of the projection lens 13 forms and which at a working distance above the substrate surface 18 is arranged. Between the front and the substrate surface 18 is as immersion liquid 22 Water is arranged, which covers the area between the optical element 7 and the wafer 17 flows through. By means of the immersion liquid, the image of structures on the photomask can be made with a higher resolution and depth of focus than is possible when the space between the optical element 7 and the wafer 17 with a medium having a lower refractive index, z. B. air, is filled.

The optical element 7 allows due to its high refractive index, a particularly good coupling of the radiation in the immersion liquid 22 , Because the optical element 7 has a radius of up to 100 mm and a nearly comparable height and can produce spinel disks only up to a height of about 40 mm, the optical element 7 can not be made from a single spinel blank, but must be made by mechanical machining of a composite structure. Due to the large diameter of the optical element 7 This composite structure can not be produced here or only with great effort by a conventional "fusion bonding" method in which the components are blasted together, so that the above in connection with 1 described method can be advantageously applied. The optical element 7 can in this case as in the above-cited WO 2006/061225 A1 the applicant (see there 5 ), which is incorporated herein by reference in its entirety.

In addition to the production of composite structures of UV-transparent materials, the method described above can also be used for the production of composite structures that are not or only partially transparent to UV radiation. In particular, this is possible with holding devices for a wafer whose components typically consist of cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ), silicon carbide (SiC), glass or glass ceramic, in particular Zerodur, ULE or Clearceram. Two examples of such holding devices are described below with reference to 3 and 4 shown.

In 3 is one as a wafer chuck 25 trained holding device shown. This consists in the simplistic representation of 3 only from the composite structure 6 on which the wafer 17 is to be held, as well as from a vacuum pump 29 , With the vacuum pump 29 is between the wafer 17 and the composite structure 6 creates a vacuum that the wafer 17 to the composite structure 6 sucks, as in 3 indicated by an arrow. The composite structure 6 has a first, upper plate 26 and a second, lower plate 27 which agree in shape and size. Between the plates 26 . 27 is arranged a plurality of support elements, which has a rib structure 28 (Lattice) with a honeycomb structure forming perpendicular to the plates 26 . 27 runs. Through the honeycomb of the grid 28 as well as in the plates 26 . 27 provided openings, the vacuum suction can take place. Furthermore, by the honeycomb-like structure, the composite structure 6 very light and can z. B. less than about 30% by weight, which when using a solid cordierite component as a wafer chuck 25 would arise. The upper and lower plate 26 . 27 as well as the rib structure 28 are each interconnected by the above-described "fusion bonding" method.

It is understood that the composite structure 6 may also be part of a wafer chuck that operates by means of electrostatic attraction and in which a high voltage source for generating an electric field between the composite structure 6 and the wafer 17 is provided. Such a wafer chuck is also suitable for vacuum applications.

4 shows a wafer table 30 , which is for storage of the wafer 17 during the exposure process in a projection exposure apparatus (not shown) for microlithography. The wafer table 30 is in a recording 31 sunk, which is formed such that its upper edge with the wafer 21 flush. The wafer table 30 consists of a first, lower component 32a made of cordierite, which with a second, upper component 32b made of cordierite by means of the "fusion bonding" process described above, both components 32a . 32b together the bulk of the wafer table 30 form. Alternatively, the two components 32a . 32b be made of other materials, preferably from Zerodur.

The two components 32a . 32b of the main body have mutually opposite recesses, resulting in between the connected components 32a . 32b several cavities 33 form. The cavities 33 serve as cooling channels for passing a cooling liquid to dissipate the heat by absorbing the radiation in the components 32a . 32b amplified occurs at the high beam intensities in microlithography. It is understood that in the wafer table 30 more cavities, z. B. for receiving built-in parts or heating elements, can be provided and that this may also be provided with a grid structure as described above, to achieve an additional weight reduction.

On the upper component 32b the wafer table 30 are several equidistant support structures 34 ("Pimple") to support the wafer 17 arranged. These each have a lower component 32c made of cordierite, with an upper component 32d of silicon carbide is also connected by "fusion bonding".

On the two a basic body of the support structure 34 forming components 32c . 32d is another component 32c made of silicon carbide, which for point storage of the wafer 17 has a reduced diameter. The upper component 32d and the other component 32e the support structure 34 are also connected by "fusion bonding", in which case, due to the small surfaces to be bonded, a "fusion bonding" process with wipes can also be used. It is understood that the components 32c -E the support structure 34 may also consist entirely of silicon carbide or another, preferably particularly hard material.

The wafer table thus formed 30 can withstand the high accelerations in microlithography, the type of components chosen realizing a lightweight structure while ensuring good heat dissipation and low thermal expansion, the high bond strength of the compounds ensuring high mechanical stability. It is understood that not necessarily all connections between the components 32a -E of the wafer table 30 must be formed by "fusion bonding", but one or more compounds in other ways, in particular as in the PCT / EP2007 / 006963 the applicant described be prepared.

It is only by means of the method described above that it becomes possible to connect components to one another by large areas of approximately 400 cm ² and more by fusion bonding. It is understood that the method described above or the composite structure can be used advantageously not only in microlithography, but also in other areas, for. B. in the X-ray telescope or in laser processing systems.

Claims (23)

Method for connecting at least one first and one second component ( 1 . 2 ; 26 to 28 ; 32a -E) to a composite structure ( 6 . 30 ) by "fusion bonding", comprising the steps of: a) applying at least one layer ( 3 . 4 ) with a porous structure on a surface ( 1a . 2a ) each of the components ( 1 . 2 b) Rooting the at least one applied Layer ( 3 . 4 ), c) merging the surface ( 1a ) of the first component ( 1 ) with a surface ( 2a ) of the second component ( 2 ), and d) connecting the components ( 1 . 2 ) to the composite structure ( 6 ) by "fusion bonding". Method according to claim 1, wherein for the component ( 1 . 2 ) and the layer applied thereto ( 3 . 4 ) Materials with the same chemical composition are chosen. Method according to Claim 1 or 2, in which, for the components to be joined ( 1 . 2 ) the same material is selected. Method according to one of the preceding claims, in which the material of the components ( 1 . 2 ) is selected from the group comprising: spinel (MgAl ₂ O ₄ ), alumina (Al ₂ O ₃ ), LuAG (Lu ₃ Al ₅ O ₁₂ ), cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ), silicon carbide (SiC) , Glass and glass ceramic, in particular Zerodur, ULE or Clearceram. Method according to one of the preceding claims, in which the layer ( 3 . 4 ) is applied by a process selected from the group comprising: physical vapor deposition, in particular thermal evaporation, electron beam evaporation, sputtering or cluster beam deposition, and chemical vapor deposition. Method according to one of the preceding claims, in which the application of the layer ( 3 . 4 ) at a coating temperature (T _B ) of less than 1000 ° C, preferably less than 300 ° C is performed. Method according to one of the preceding claims, in which the surface ( 1a . 2a ) of the component ( 1 . 2 ) for applying the layer ( 3 . 4 ) having a surface roughness of less than 1.0 nm rms and preferably a surface flatness of less than λ, in particular less than λ / 2, at λ 632 nm. Method according to one of the preceding claims, in which the surface ( 1a . 2a ) is cleaned and degreased before coating. Method according to one of the preceding claims, in which the layer ( 3 . 4 ) by co-coating two or more constituents of the material of the layer ( 3 . 4 ) is applied. Method according to one of the preceding claims, in which the layer ( 3 . 4 ) is applied to a thickness of 500 nm or less, preferably 100 nm or less. Method according to one of the preceding claims, in the roughening is carried out by means of a procedure that selected is from the group comprising: dry etching, wet etching and Ion beam bombardment. Method according to one of the preceding claims, in which the surfaces ( 1a . 2a ) are fixed after being brought together at a static pressure of more than 1 bar. Method according to one of the preceding claims, in the "fusion bonding "at a maximum temperature of 2100 ° C, preferably not more than 1500 ° C, in particular of a maximum of 1300 ° C he follows. Method according to one of the preceding claims, wherein the "fusion bonding" at a temperature of 70% or less, preferably of 60% or less of the melting temperature of the layer ( 3 . 4 ) he follows. Composite structure ( 6 . 30 ), in particular produced by the process according to one of claims 1 to 14, with at least one first and second component ( 1 . 2 ; 26 to 28 ; 32a -E) attached to two surfaces ( 1a . 2a ), whereby between the surfaces ( 1a . 2a ) an intermediate layer ( 5 ) introduced by "fusion bonding" of the components ( 1 . 2 ) with at least one on a surface ( 1a . 2a ) each of the components ( 1 . 2 ) applied, roughened layer ( 3 . 4 ) is formed with a porous structure. A composite structure according to claim 15, wherein the component ( 1 . 2 ) and the layer applied thereto ( 3 . 4 ) consist of materials with the same chemical composition. Composite structure according to Claim 15 or 16, in which the components to be joined ( 1 . 2 ) consist of the same material. Composite structure according to one of Claims 15 to 17, in which the intermediate layer ( 5 ) extends over an area of at least 100 cm ² , preferably of at least 200 cm ² . A composite structure according to any one of claims 15 to 18, wherein the material of the components ( 1 . 2 ) is polycrystalline. Optical element ( 7 ) made of a composite structure according to any one of claims 15 to 19. Holding device for a wafer ( 17 ), in particular wafer chuck ( 25 ) or wafer table ( 30 ), made of a composite structure ( 6 . 30 ) after one of claims 15 to 19. Projection lens ( 13 ) for microlithography for imaging a structure on a photosensitive substrate ( 17 ) with at least one optical element ( 7 ) according to claim 20. Projection exposure apparatus ( 10 ) for immersion lithography with a projection objective ( 13 ) according to claim 22, in which the optical element ( 7 ) the photosensitive substrate ( 17 ) is arranged opposite, wherein between the photosensitive substrate ( 17 ) and the optical element ( 7 ) an immersion liquid ( 22 ) is introduced.