EP2231544A1

EP2231544A1 - Low-temperature method for joining glass and the like for optics and precision mechanics

Info

Publication number: EP2231544A1
Application number: EP08862790A
Authority: EP
Inventors: Manfred Krauss; Gudrun Leopoldsberger; Gerhard Kalkowski; Ramona Eberhardt; Andreas Tuennermann; Charlotte Jahnke; Simone Fabian
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2007-12-17
Filing date: 2008-12-12
Publication date: 2010-09-29
Also published as: US20100288422A1; DE102007060784A1; WO2009077458A1

Abstract

The present invention relates to a method for joining two or more components made of glass, ceramic, and/or glass ceramic, using a soluble glass joining solution having sodium, potassium, and/or lithium ions and/or a silica sol, the joining solution being applied to joint surfaces between the components to be joined and solidified at mild temperatures, the method being either characterized in that the joining solution comprises an additive selected among boric acid, boron compounds from which boric acid can result by hydrolysis, aluminum acetates, aluminum silicate/NH3 /H2O titanium compounds forming titanium hydroxy cations, water-soluble zinc compounds, water-soluble zircon compounds, and water-soluble yttrium compounds, wherein said additive is added in an amount that reduces the pH value of the underlying soluble glass, and/or characterized in that, after the joining solution is applied and the components to be joined are brought together and fixed, the joined components are dried by removing water at room temperature, wherein, after drying, the joined components are tempered in vacuum at a temperature in the range of up to 200°C above room temperature.

Description

Low-temperature method for joining glass and the like for optics and precision mechanics

The joining of at least two components made of glass, ceramic and / or glass ceramic in optical production by inorganic bonding at low temperatures is known. According to the invention, it takes place with high precision and long-term stability mechanically fixed by inorganic solutions based on sodium, potassium or lithium water glass solutions or silica sols, with which a longer adjustment time is possible. For this purpose, the respective base solution additionally contains, individually or in combination, special inorganic and / or organic compounds of the following elements: Ti, B, Al, Y, Zr or Zn. The corresponding solutions are made of the same and / or different materials between the surfaces to be joined of the components reacted. On the one hand, the additives can be used to optimize the reaction time needed to adjust the components; On the other hand, it has been found that compounds with high strengths are realized with the inventive ironing solutions, the materials do not change and there are few limits to potential applications at elevated temperatures, moisture fluctuations and under vacuum.

The production of precision optical and mechanical systems in optics and microelectronics requires the exact assembly of two or more glass and / or glass ceramic parts to ensure a long-term stable position of the components. Conventional joining methods at high temperature can lead to changes in the parts to be joined, stresses due to differential thermal expansion or destruction. For new optical systems, eg. As ultra-light levels in telescopes, beam splitters in projectors, micro-optical systems or glass-ceramic components for lithography tools, assembly and connection techniques for optical components made of very different materials are needed. A wide range of high or low refractive optical glasses and glass ceramics z. T. with very low thermal expansion coefficients are available or are being developed for new applications. However, the current connection technology places potential applications in many cases procedural limits.

Low temperature bonding, also known as "low-temperature bonding" (LTB), is a technique of joining two bodies by applying a suitable bonding solution between the surfaces of the parts to be joined, thereby creating a chemical reaction between the surfaces and components of the bridging solution at low temperatures a solid compound For the purposes of the invention, these mean compounds which are typically prepared in the range from room temperature to about 100 ^° C. Methods for joining workpieces at low temperatures through the use of solder glasses are known in the art. However, the necessary temperatures are above 150 ⁰ C. The use of inorganic and inorganic-organic networks, eg. T. prepared via the sol-gel process, the compounds of components is listed for example in the document EP 0414001 A2.

Also known in the art are compounds of inorganic silicon-containing components (e.g., Si wafers) by means of silicate solutions, usually sodium silicate. The connection between the components is realized by the formation of silicon-oxygen compounds in the course of the reaction between the surfaces to be joined. In U.S. Patents 6,284,085 B1 and 6,548,176 B1, bonding of two materials by hydroxide catalyzed hydration / dehydration is involved

Room temperature after formation of hydroxide ions on the two surfaces to be joined described. If necessary, powder of a silicate or silicate-containing material is used as filling material.

Joining tests carried out by the inventors with pure potassium hydroxide KOH or

Caustic soda NaOH as a foaming solution were not successful (turbidity of the joint surface, corrosion phenomena). This also applies to the etching of the joining surfaces with hydrofluoric acid HF (eg 20% strength) and subsequent joining without and with ironing solutions.

In addition to the joining of phosphate glasses, the production of glass-ceramic composites (see, for example, US Pat. No. 6,699,341 B2) for optical and optoelectronic components is also described in the prior art. In this case, phosphoric acid or siliceous solutions are placed between the parts to be joined. After dehydration at low temperatures (20 to 100 ⁰ C) and a relatively long time (6 hours to one week) very strong composite structures. Without an embodiment of this would be specified, it is mentioned in this document that the addition of Al ₂ O ₃ in an amount of up to 10 wt .-% to the ironing solution of lithium, potassium, magnesium, calcium or barium silicate or Mixtures of these can improve the chemical durability of a compound of Zerodur substrates, based on the chemical similarity between substrate and Fügelösung (Zerodur is a lithium-aluminum-silicate glass-ceramic). A special solution for low-temperature joining of alumina-containing bodies, eg. B. sapphire single crystals, using an aluminate-containing solution is described in the German application 10 2005 000 865 A1. The aluminate-containing solution is stabilized by a base. At least one of the surfaces intended for assembly must be treated with the chemically aggressive peroxomonosulphuric acid. At least one of the bodies to be joined must be an alumina-containing body.

It is desirable to have a joining technology for glass and glass-ceramic optical components that offers advantages in terms of at least one of the parameters accuracy, stability and lightweight for many applications and that overcomes current procedural limitations in optical production.

Two or more components of the same and different classes of materials, chemical composition, structure and / or properties (glass, glass ceramic, possibly also ceramic) according to the invention by inorganic low-temperature joining for optics and precision mechanics at low temperatures (<150 ⁰ C) are produced mechanically precisely, so that mechanically very strong connections arise and / or only small optical losses occur in the transition zone. Preferably, one of these materials to be joined is a material with extremely low thermal expansion (so-called zero-expansion material).

The surfaces to be joined are usually to be cleaned before joining, which should be done in the simplest possible way and without special chemicals. In addition or additionally, they should be treated in such a way that a favorable contact angle with the joining solutions is created. This contact angle should in many cases be small (i.e., less than 45 °) so that good wetting of the joining surfaces occurs. However, the contact angle must not be too low, so that the joining process is technically feasible, the joining and adjustment times can be made variable and no air is trapped between the joining surfaces. In special cases, however, the contact angle should be relatively large (50 ° up to about 75 °, in extreme cases even 90 °).

The object of the invention is to control the speed of the chemical reaction of the joining process and to make it variable according to the complexity of the joints. So can the process of curing the

Delays Niedertemperaturfügung and thus a prolonged period for the fine adjustment of the components to be joined are made possible. Alternatively, the process should also be able to be accelerated. In addition to the variation of the joining process (bonding surfaces, temperature, time, coating weights, atmosphere, vacuum), which may possibly contribute a part, the variation of the properties of the jointing solution and thus of the resulting joint is of decisive importance.

It has surprisingly been found that the joining time, i. the period in which a shift or (re) adjustment of the components to each other is possible, can be changed by a change in the pH, in a simple manner by the addition of Ti, B, AI, Y -, Zr or Zn-containing inorganic or organometallic solutions to Fügelösungen from conventional - usually commercial - water glasses or silica sols can be achieved.

For example, Nathum silicate solutions (sodium water glass, eg Na2SisO ₇ from Riedel-de Haen), lithium silicate solutions (lithium water glass, eg Betol Li22 from Woellner), potassium silicate solutions can be used as base fuser solution

(Potassium waterglass, eg K 42 from Woellner) or silica sols (eg LEVASIL® 300/30%, 200A / 40% from Bayer). These are solidified with said additives at joining temperatures of preferably <150 ⁰ C to mechanically stable and temperature-stable joints of two or more components. The forming networks between the joining surfaces are each composed of silicon, oxygen and the cation (s) added to the waterglass solution or the silica sol prior to the addition.

With the help of the additives, the reaction time of the solution needed for the adjustment of the components can be optimized; On the other hand, it has been found that with the padding solutions according to the invention often only small optical losses occur and compounds with increased strengths are realized. The latter can be observed in particular in such Fügelösungen containing silicon in addition to the same cation species that are also found in the parts to be joined.

By means of the invention, the speed of the chemical reaction of the joining process can be controlled by varying the composition of the bridging solution by means of suitable additives containing the ions to be used according to the invention, so that e.g. the necessary longer adjustment times (usually significantly more than 1 min) can be achieved when assembling complex components with optical and mechanical functions.

It is true that in some cases a prolongation of the filling time can also be achieved by simply diluting the ironing solutions with water; however, through this Measure extends the drying time. In addition, it is then often difficult to obtain a defect-free joint gap during drying, especially for larger joint surfaces with larger distances to the edge of the joint, because the water is difficult to remove from the gap. There are blisters and other irregularities.

Before joining, the material surfaces to be joined are preferably provided with high quality "optical polish" by grinding and polishing.

The geometric requirements on the surfaces are generally such that a high surface quality, the lowest possible joint gap and the most homogeneous possible layer thickness can be achieved. The aim is to achieve joint gaps of <2 μm, preferably <160 nm. The peak-to-valley (PV) should be less than 160 nm, i. better than λ / 4 (for wavelength λ = 633 nm) and the roughness should be <30 nm (RMS = root-mean-square), preferably <3 nm. This applies in particular to optical precision instruments. To add two thick and stiff planar substrates, the flatnesses in the initial state should be adjusted accordingly by pre-processing accordingly. For flat and flexible substrates, larger flatness deviations are permissible if the desired joint gap can be achieved by appropriate pressing of the parts together. But even non-planar substrates can be joined, z. B. two spherical shells or aspheric surfaces that fit well together.

In practice, in round blanks with a diameter of 25 mm, z. B. from BK7 or ULE typically reaches a flatness of λ / 4 to λ / 10 (about 160 nm to 60 nm) and roughness of 5 nm to 1 nm. The high demands on the geometry of the joining surfaces must be met in order to achieve a sufficient approximation of the contact surfaces. The commercial slides used for comparative purposes made of conventional soda-lime silicate glass, despite being produced via the float process, only have flatnesses of 1 to 2 μm.

Typical materials that can be added at low temperatures are listed in Table 1. These are glasses (flat glasses, silica glasses, optical glasses) and a glass ceramic (Zerodur). Of course, the materials given in the table are pure examples to which the invention is not limited. Table 1 . Add materials

Typical properties of the materials to be joined are summarized in Table 2.

Table 2. Properties of the joining materials

If necessary, a suitable cleaning of the materials to be joined takes place before the low-temperature joining. This is especially the RCA hot cleaning (basic standard cleaning method for silicon wafers, 1960, W. Kern, Radio Corporation of America) of the two surfaces to be joined (clean, hydrophilic, activation of the joining surfaces, approaches to reduce the defects, water, Acids / alkalis, cleaning agents, ultrasound) in question. In this case, organic and metallic impurities are removed from the surfaces to be joined (complexing of, for example, Cu, Ag, Au, Zn, Cd, Ni, Co, Cr by NH ₃ , formation of insoluble hydroxides and / or oxides or soluble chlorides, eg B. with the ions Al ³⁺ , Fe ³⁺ ). The contact angle between Joining surfaces and joint solution is by this method less than 45 °, preferably between 1 ° and 20 °. As an alternative to RCA hot cleaning, the so-called "bath cleaning" is carried out, in which special surfactants (eg Optimal 9.9 and GS10 from Olschner / Gottmardingen) and with ultrasound support are used to clean Zerodur specimens can not be removed without corrosion

Clean joining surfaces by RCA process. The cleaning of the Zerodur samples is therefore preferably carried out with a modified RCA method (without the HF HF cleaning step) or by bath cleaning.

Optionally, the joining surfaces are additionally activated. This is done for example with a nitric acid treatment, for example, 30 min treatment in 10% HNO ₃ , rinsing with deionized water, dripping times 1, 5 to 2 h. In terms of increasing the adjustment and hardening time of the joints and a silanization of the joining surfaces is possible to achieve a hydrophobic contact angle (about 50 to 75 °) between the joining surface and joint solution. As silanes, for example, fluorosilanes (eg, perfluorododecyl-thethoxysilane), organically crosslinkable alkoxysilanes such as MEMO (3-methacryloxy-propyltrimethoxysilane) or amino-modified alkoxysilanes such as AMO (amino-propyltrimethoxysilane) can be used.

Depending on the respective joining task, the contact angle should therefore be small (for a good, even distribution of the jointing solution on the joining surface in the case of rapid hardening) or large (the latter preferably by silanization, which means a "push-on", ie a mutual movement) Joining materials, allowing longer, while slow hardening causes long adjustment times).

A comparison of the measures taken for RCA cleaning and bath cleaning is shown in FIG.

Since all material classes to be joined according to the invention contain SiO 2 as the main constituent, basic silicates are alkali silicate solutions (water glasses) of different composition (Na, K, Li) and concentration (1 to 30% by weight) or silica sols of different solids contents (eg 300/30 %, 200A / 40%, wherein the first number indicates the specific surface area of the SiO ₂ and the second number indicates the SiO ₂ content, based on 100 parts of silica sol) with additions of inorganic and organometallic compounds of the cations according to the invention. Silica sols are aqueous, colloidally disperse solutions of amorphous silica in water. The soluble alkali metal silicates hydrolyze in water as silica is a weak acid. They tend to condensation in solution. The way mentioned soda or soda water glasses contain as main constituents SiO ₂ and Na ₂ θ. They are the water glasses of greater technical importance. The ratio of SiO 2: Na 2 O varies from 3.9 to 4.1 for water-based glasses containing siliceous acid, from 3.3 to 3.5 for neutral soda water glass, and from 2.0 to 2.2 for alkaline water glass. In potassium water glasses, the SiO ₂ : K ₂ O ratios are between 1: 1 and 3.9: 1. In lithium silicate solutions, the molar ratio SiO ₂ : Li ₂ O is between 2.5 and 4.5.

Very stable low-temperature bonds (strength, long-term stability) are obtained when using neutral to slightly basic sodium silicate with a

Molar ratio SiO ₂ : Na ₂ O of 3.5 (solids content about 39%), with potassium waterglass having a molar ratio SiO ₂ : K ₂ O of 2.9 (solids content about 40%) and in the case of lithium waterglass with a molar ratio SiO ₂ : Li ₂ O of 2.5 (solids content about 27.2%) found as a base material for the joint solution. The pH values of the alkaline alkaline water glasses are between 11, 8 and 12.8 (see Table 5, below).

Monomolecular silica is only present in high dilution. If the OH concentration is reduced, more or less rapidly (depending on concentration and pH) higher condensed silicic acids are formed, which become more and more difficult to solubilize as the degree of condensation increases, ultimately resulting in a fixed addition at low temperatures. Silica sols have a pH of about 10 (Table 4). Very good (solid) compounds were obtained with silica sols with a specific surface area of SiO ₂ and with SiO ₂ contents (based on 100 parts of silica sol) of 100/45%, 300/30% and 200A / 40% (A denotes the particular low alkali content of silica sol).

The joining or adjustment times should be greater than 1 min and should preferably be at least 3 min, so that even complicated components can be joined with high precision.

Exemplary base waterglass solutions are shown in Table 3. The basic Fügelösungen be changed by the additives of the invention so that an extension of the setting and hardening times of the joints occurs and thus the time available for fine adjustment to the necessary level (greater 1 to 5 min) is extended. Examples of water glass or silica sol solutions (sodium water glass (Na ₂ Si ₃ O ₇ ; M = 242.23 g / mol; SiO ₂ : Na ₂ O = 3.48, solids content 39%) and hardness ( pot) times

The inventors have surprisingly found that the duration of addition of each system increases with decreasing pH. The constituents to be added according to the invention to the base materials each lower their pH. Conversely, can be shortened by increasing the pH by correspondingly more basic additives, the setting and curing time, which can be advantageous for simple geometries of the components to be joined in some situations. The materials do this in different ways and, by the way, fulfill other, different tasks, which will be explained in more detail below.

A. Silicon compounds

The formation of higher condensed silicas (isopoly acids) is a slow process. By inventive addition of acidic solutions with cations of the elements Ti, B, Al, Y, Zr or Zn, such as boric acid, saturated B ₂ O ₃ suspension, titanium sulfate hydrate, ytthoacetate, aluminum acetate, titanium chloride to a waterglass solution, the monomolecularly distributed silica is liberated: [H ₂ SiO ₄ ] ^{2 "} + 2 H ⁺ → H ₄ SiO ₄

It initially remains in solution as such. However, even before the addition of acidic components, water glass contains proportions of aggregated silica, so that low-temperature additions can occur directly with waterglass without acidification. Water glass acts as a binder. The setting mechanism is based on neutralization (by CO _{2 of} the air), dehydration and cooling. According to the invention, the removal of water by increasing the temperature (up to 200 ⁰ C, preferably below 100 ⁰ C), vacuum or dehydrating chemical substances (eg silica gel) provoked. In aqueous silica sols, the amorphous silica is stabilized with minor additions of NaOH. If the OH concentration is reduced by the addition of acidic additives, more or less rapidly condensed silicic acids (isopoly acids) are formed, which become increasingly less soluble with increasing degree of condensation (see above).

As mentioned above, solutions of chemical compounds are added to the respective base bridging solution, singly or in combination (concentrations 1 to 50% by weight, preferably 1 to 35% by weight). These have an influence both on the properties of the jointing solution and on the subsequently formed solid compounds or the joined components. In the following, the additions to the basic solutions are listed and their effects on the bridging solution are shown:

B. boron compounds

For joining boron-containing materials (BK7, Borofloat) are:

a) boric acid H ₃ BO ₃ . It is light in water when heated, sparingly soluble in the cold and is a weak acid. It serves to neutralize the basic water glass solution or slightly basic silica sols, delays their chemical reactions with the joining surfaces and the CO _{2 of} the air and the formation of water-insoluble boro-silicate bonds Si-OB from water-soluble alkali borates. This lengthens the joining and adjustment times. Additional stabilization and reinforcement of the joint is carried out by dehydration and transition into metaboric [Bθ2] _n at 70 ⁰ C. Trimethyl borate B (OCH ₃₎ ₃ is hydrolyzed by water to form boric acid and methanol, resulting in the extension of the joining times as boric acid is formed during the joining process. b) B2O3. This compound dissolves in water exothermically to orthoboric acid H3BO3 (up to 5% by volume) c) trimethyl borate B (OCH ₃ ) 3 C. Aluminum compounds

Aluminum diacetate HOAI (OOCCH ₃ ) ₂ (acetic alumina) and aluminum thacatate AI (OOCCH ₃ ) ₃ react basicly in aqueous solution and catalytically delay the solidification of the alkali metal silicate solutions. In alkaline solutions, Al (OH) _{3 can be} formed, which aggregates to higher molecular weight particles, eventually leading to colloidal distribution, forming "Al (OH) ₃ -GeIe" by dewatering to increase the stability of the Si addition -O-Al and to slow down the chemical hardening reaction Suitable for the present invention are:

a) Basic aluminum thiocyanate AI (OOCCH ₃ ) ₃ b) Basic aluminum diacetate HOAI (OOCCH ₃ ) ₂ c) Aluminum silicate, each in the presence of NH ₃ H ₂ O.

When heated, dehydration occurs under oxide formation. This leads to an increase in the stability of the Si-O-Al addition. By adding ammoniacal solution (NH ₃ H ₂ O) to one of the abovementioned aluminum-containing solution, the intermediately formed Al (OH) ₃ can be dissolved in water with complex formation: Al (OH) ₃ + OH ^" → [Al (OH) ₄ ] ^" , this solution acts as well as aluminum acetate itself as a chemical buffer solution (salt of weak acid and strong base). Buffer solutions reduce the OH ^"ion concentration of the water glass or silica sol solutions and prolong curing times, eg .: [AI (OH) _4] -. → Al (OH) ₃ + ^OH" NH ^{4 +} + OH ^"→ NH ₄ OH → NH ₃ T + H ₂ O

Aqueous weakly basic ammonia solution NH ₃ H ₂ O is generally added as an additive to the cationic solutions used in order to prevent the formation of hydroxide precipitates by formation of soluble complex compounds (eg [Al (OH) ₄ ] ^" , [Zn (NH ₃ ) ₄ ] ²⁺ ] in the pad solutions (not for Ti, Zr-Y containing solutions).

D. titanium compounds

For joining titanium-containing material (eg ULE): Ti ⁴⁺ ions do not occur in aqueous solution, there are always hydroxocations such as [Ti (OH) ₃ (H ₂ O) ₃ ] ^" or [Ti (OH) ₂ (H ₂ O) ₄ ] ²⁺ whose composition is strongly dependent on the pH, titanium oxide hydrate is an amphoteric compound which reacts only weakly basic, with removal of water form -O-Ti-O-Ti-O-chains, with dissolved Si species of the alkali silicates in the Fügelösungen to longer curing times and solid compound or solid compounds -O-Si-O-Ti-O- to lead. Titanium oxide hydrate is poorly soluble in the aged state after the low-temperature joining in acids and alkalis. Especially suitable for the present invention are:

a) Titanium sulfate hydrate TiSO ₄ × H ₂ O b) TiO ₂ in H ₂ O, 1% by weight c) Tetraethyl orthotitanate d) Tertaisopropyl orthotitanate (titanium IV isopropylate) e) Titanium (IV) ethylate f) Titanium ( IV) butyl ortho-titanate g) titanium acetylacetonate

Freshly precipitated TiO ₂ H ₂ O in the bridging solutions readily dissolves upon addition of NH ₃ and Na ₂ CO (intermediate formation of (NH ₄ ) ₂ CO) (see notes under C).

E. Zinc compounds

The slightly soluble acetates, nitrates and sulfates of zinc form zinc hydroxide in alkaline solutions. Zn (OH) ₂ is amphoteric and tends to complex (e.g., with

Tartaric acid), in excess of alkali, zinc hydroxide formed in the meantime dissolves, forming a zincate Na [Zn (OH) ₃ ]; Zinc compounds improve the chemical resistance of the jointing solution and retard hardening. According to the invention can be used in particular:

a) zinc acetate b) zinc nitrate Zn (NOs) ₂ c) zinc sulfate 7-hydrate

F. zirconium compounds

Zirconium compounds serve to improve the chemical resistance of the jointing solution and to delay the curing. Particularly suitable are: a) zirconium sulfate Zr (SO ₄ ) ₂ b) zirconium (IV) isopropoxide-isopropanol complex c) zirconium propylate 77% in n-propanol d) zirconium-2,4-pentanedionate e) zirconium-n- propylate f) zirconium (IV) acetonate 98% g) zirconium (IV) oxide in water 1% h) zirconium ethoxide i) zirconium nitrate Zr (NOs) ₄ k) zirconium (IV) oxide chloride 8-hydrate.

G. Yttrium compounds

Yttrium compounds serve to improve the chemical resistance of the

Joint solution and the delay of curing. According to the invention are particularly suitable:

a) Yttrium chloride hexahydrate b) Yttrium acetate hydrate 1% c) Yttrium nitrate Y (NOs) ₃ . 6H ₂ O.

Dilution and additions to the slip-base solutions result in a reduction of the pH (Table 4), which in turn leads to retardation of the cure. The attack of the less basic Fischenösungen on the surfaces of the glassy or glass-ceramic joining components delays the diffusion of the ingredients in the surfaces of the adherends, the neutralization of the Fügelösung (preferably by the CO _{2 of} the surrounding air), the dehydration and the transition solution sol-gel - Solid colloidal glass layer and thus the formation of new Si-O-Si bonds between the components.

In the case of solutions containing Zr or Y, precipitation as hydroxide in the bridging solutions can be prevented by formation of complexes of different stability by addition of tartaric acid or citric acid.

Table 4. pH values of different solutions

The components of the Fügelösungen form and stabilize after chemical reaction with each other and with the components of the surfaces of the parts to be joined the network of the joint connection and meet different requirements. Table 5. Effect of components of the ironing solutions on the formed solid joint

Continuation Table 5

The sequence of the joining process will be explained in detail below.

The process preferably begins with a cleaning of the parts (bath cleaning or RCA cleaning) as described above by a pretreatment of the

Joining surfaces (eg with alkalis, acids, silanization). This is followed by the application of the Fügelösung (eg with metered pipette / syringe / dispensing needle by drop application and spin if necessary [spin coating]), wherein the typical amount of applied Fügelösung greater than or equal to 0.8 ul / cm ² joining surface. Thereafter, the joining is effected by placing a joining body on the other from above or pushing a joining body from the side. This is done, for example, by placing a drop on the lower sample and immersing the upper sample at the edge of the drop and then sliding it over the drop. The joining surface between the samples fills by capillary action. Within the period that is available for the adjustment, there is then possibly a movement and alignment of the joining body against each other. Thereafter, the joining partners are fixed (preferably under slight pressure, for example about 10 ⁴ N / m ² ) for about 15 minutes to about 12 hours at room temperature. The subsequent rest periods are about 0.5 to 4 hours, in air or in a desiccator. The short times are particularly suitable for small joining surfaces (a few cm ² ), the long ones for rather larger areas (50-100 cm ² ). For this purpose, a careful and possibly vibration-free introduction of the bonded parts in a vacuum chamber or a drying oven is required. The solvent water is slowly removed by a drying process. In the process, a chemical compound of the joining surfaces builds up. This structure is preferably supported by vacuum (rough vacuum about 1 mbar is sufficient) at room temperature for about 3-10 days with or without the application of weights. Finally, a heat treatment in the oven (preferably in a vacuum, normal atmosphere) preferably at about 80 ⁰ C, a maximum of 200 ⁰ C follows. It takes a few minutes to two weeks.

Drying in vacuo has the advantage over normal atmosphere with usually about 50% relative humidity that the outside area around the joint surface is completely free of water vapor and a back reaction in which moisture / water diffuses into the joint surface from the outside is excluded. The increased moisture gradient between joining surface and outer space drives the desiccation of the joining surface very efficiently and thus ensures good dehydration and high solidification in a short time. Also during the joining process dissolved, adsorbed or reactively formed gases that are mobile and reach the edge of the joining surface via diffusion processes, are sucked out there by vacuum drying. This contributes to an increased quality of the connection and guarantees a trouble-free later Application of the bonded components in a vacuum (eg in space). During the joining process, components of the jointing solution diffuse into the surfaces to be joined (see illustration in FIG. 2). Via covalent Si-O bonds and other bonding mechanisms (single and multiple bonds, hydrogen bonding, bonding of alkali ions with non-bridged oxygen, Si-O-Si network bonding), a network is created that connects the components to be joined at the atomic level ,

The diffusion and reaction processes in the joining zone can be effectively supported in the drying phase by infrared radiation. The

Dehydration of the joining zone naturally becomes more difficult, the greater the extent or the distance to the edge. It has been shown that infrared radiation acting at room temperature during vacuum drying leads to improved bonding results, in particular in the case of relatively extended joining zones, and reduces the occurrence of visually visible defects.

Above all, approximately "black radiators" with a temperature of 250-500 centigrade are suitable as beam sources The radiation is preferably directed to the center of the joining surface, and the power density is preferably set so that the samples do not substantially heat up on vacuum drying, ie the

Temperature preferably does not rise above 30 Celsius, but in no case above 50 Celsius.

The layer thicknesses of the joints, depending on the jointing solution, the application method and quantity and the weight distribution, can generally be between 10 nm and 2 μm with a focus at about 150 to 500 nm.

Climatic tests (based on DIN ISO 9022-2) show that such joints are long-term stable even under changing environmental conditions. In additions of so-called "NuH" expansion matehals (eg ULE, Zerodur), even low-temperature tests were carried out in which the connected parts were immersed in liquid nitrogen (ie cooled to about 80 Kelvin) and then returned to room temperature in air This is evidenced by the excellent long-term stability of the joints according to the invention The first successful joints have been stable since January 2006 (as of September 2007) and thus more than 20 months so far.

The process according to the invention is particularly suitable for the following applications:

Fiber Bonding Fiber bonding consists mostly of SiO ₂ glass fibers, which are extremely stable in "V-shaped" grooves with extremely low tolerances to be embedded. Often, these V-grooves are made by anisotropic etching of silicon. The natural (or artificial) oxidation of silicon at the surface provides an excellent bond surface for silicate bonding and the relative "low viscosity" bonding solution results in very good wetting of the fiber.

Nut pressed and held until the solution is introduced, dried and the bonding process is completed.

Fiber to ferrule bonding. Similarly, when bonding "fiber to ferrule", ie fiber into fiber connectors, the fiber connector can be in the form of two half-shells or as a hollow cylinder into which the fiber is inserted before the bonding solution is applied and the composite is dried low viscosity of the Fügelösung very tailor-fit pairings are possible, which allow a small layer thickness of the bond and a good heat dissipation from the fiber to the ferrule and - compared to polymers - allow elevated temperatures.This example, for fiber lasers in high performance advantageous, where often large power losses to the The bonding layer to the ferrule can also be made "cloudy" by suitable solutions and can scatter or absorb parasitic radiation and dissipate the heat loss to the (possibly water-cooled) ferrule.

Stable precision connection.

Temperature-resistant, ultra-thin connection with good heat transfer (for cooling).

Sensor applications (see, e.g., Smart Mater, Struct. 8 (1999) 175-181).

Prism bonding (connection of 2 prisms to one another, "prism_to_phsm", connection of a prism to a support, "phsm_to_plane", shown in Figures 3a and 3b).

Optical platforms (stable precision connections).

Transparent compounds of non-linear optical crystals (LiNiO3, BaTiO3 or similar) with prisms or glass lenses for optical modulators.

Disk laser (stable precision connections). FIGS. 4a and 4b each show a laser crystal without or with an intermediate piece bonded to a heat sink. (The adapter is used "mechanically" for thermal adaptation at different coefficients of expansion of the heat sink and laser crystal or "functionally" for the so-called "Q-switching" of the laser, for example in the form of a SESAM = Semiconductor Saturable Absorber Mirror). In the second case, the silicate bonding layer can comprise both the bonding of the laser crystal to the intermediate piece and the bonding of the intermediate piece to the heat sink. Of course, the material properties of the heat sink and adapter must be taken into account. Optionally, thin SiO ₂ layers (about 100 nm) may be applied by sputtering or similar thin-film techniques prior to the silicate bonding.

10

Stable compounds of laser crystals (Yb: YAG, Nd: YVO ₄ or similar) with support materials such as sapphire or Si (or superficially oxidized Si) for stable support and heat dissipation in disk lasers.

i5 - Creep-resistant connections of opt. Elements with ceramic, also connection of piezo ceramic with optical components or non-linear opt. Crystals, for changing optical properties via electrical control.

In the following, the invention will be explained with reference to exemplary embodiments. It should be clear that the features of different embodiments can be combined with each other. The glass or glass ceramic surfaces to be joined are chemically activated by an inorganic aqueous solution or suspension with additives and firmly attached at low temperatures. All experiments take place in the clean room. The components can u. a. from Zerodur from Schott, ULE from Corning, 25 silica glass (eg Lithosil) from Schott), BK7 or Borofloat glass from Schott. Typically, blanks of these materials were used with the following characteristics: diameter 25 mm, height 10 to 11 mm, polished on both sides and numbered consecutively by engraving.

To clean and activate the surfaces of the components to be joined, at least one of the following methods is used for the purification of silicon wafers in accordance with the RCA standard method (see Table 3) (see FIG. 1):

35 1. Commercial glass cleaner

2. Analog "RCA standard cleaning"

In some cases, the joining surfaces are additionally activated (30 min treatment in 10% HNO ₃ , rinsing with DI water, dripping times 1, 5 to 2 h). The period between cleaning / activation and joining should not be longer than 6 days, preferably <1 day.

During contacting, new chemical bonds are formed. Upon evaporation 5 of the water from the bridging solution by low temperature treatment, a solid, ultrathin intermediate layer forms. The joining process was divided into three main steps (see above):

• Cleaning, activation of the surfaces to be joined (basic, acidic, hydrophilic, possibly silanization) lo • Application of the bonding solution and contacting of the parts, adjustment

• Rest periods, weighting with weights

• Water removal / drying and chemical bonding of parts (hardening).

The ironing solution can be applied manually by means of a syringe, pipette, dispensing needle, but also e.g. by spin-coating or similar Procedure done. If necessary, drying can be carried out after application. This makes it possible to adjust the two parts to be joined "dry" and then in a moist environment (eg in water vapor) first to activate the solution and to react with the substrates, and then again a water removal / drying process. Process 20 as described below.

The joining of the parts to be joined is done by hanging up or pushing from the side. Anschießend the joining parts are adjusted against each other. The joint cures to solid connection.

25

The water removal / drying can be done first at room temperature in air and / or in vacuum with or without weight. Preferably, a period of about 3 hours to about 6 days is suitable. This is followed by a thermal treatment in the oven at temperatures of about 60 to 110 ⁰ C to stabilize the compound. 30 This can also be done in air or in a vacuum.

After the individual process steps, the properties of the activated glass and glass ceramic surfaces, the intermediate layer and the joint are characterized as follows:

35

1. Optical assessment of the joined samples and light microscopy

The samples were assessed visually immediately after the drying process using a grading scale of 1 to 5 with the size and number of Defects, bubbles and interference were defined. In addition, the location and intensity of cloudiness were also described. Grade 1: no visible defects Grade 2: smallest defects such as bubbles Grade 3 several small defects, visually clearly visible Grade 4: clearly visible defects Grade 5: 50% of the area with defects

Subsequently, the microscope was followed by the exact inspection of the samples with subsequent documentation with images. Procedure: Lens used: 2.5x, height adjustment on a defined test round with visible defects, on the test round slowly scan the surfaces for defects, bubbles and opacities, documentation of defects with drawing and image (Analysis).

2nd layer thickness

To further characterize the layer formed during bonding, an analysis of the layer thickness was carried out with a length measuring instrument "TESA-μhite PIM100", whereby the weight was varied, which during bonding, in addition to the upper round blank, stresses the joining surface.

Break test (three-point bending tests)

In order to be able to determine the mechanical load-bearing capacity of the bonded round blanks, bending round bars were cut from the glass round blanks which had optically good quality, which have the joined area in the middle of the end faces. Bending fracture bars were measured which have a square base area with an edge length of b = h = 6 cm. The length varied depending on the material used. The sawed bending bars were tested with the 3-point bending test on a tension-compression machine "Instron 4464"

Bending tension applied to the joined surface and loaded until breakage. In order to ensure a tilting of the plane-parallel top and bottom, the samples were provided in the measuring device with a degree of freedom, so that the samples could align parallel to the punch. Good results were obtained for the mechanical loadability of bonded surfaces (30 to 60 MPa). Solid glass in comparison has typical strengths of 60 MPa. Only Borofloat proved to be very poorly available because the breaking stresses were much worse than with the other materials. A renewed tempering after sawing does not improve the joining surface. Exemplary Embodiment 1 (Comparative Example) Low-temperature Bonding of Two ULE Circles

Cleaning: RCA cleaning

Fusing solution: ISC 1 (Na water glass solution)

Joining process: central dripping of the joint solution with a pipette, adjustment time 1 min,

Weight rest (400 g) for 60 min, then 48 h temperature treatment in

Drying cabinet at 80 ⁰ C and normal atmosphere Result: adjusting time 1 min, stable addition, optically clear and transparent joining surface

Optical rating: Grade 1 Three point bending strength: 55 MPa Layer thickness: 0.9 μm

Exemplary embodiment 2 Low-temperature bonding of two BK7 blanks

Cleaning: RCA cleaning Joint solution: ISC 5 (sodium water glass + boric acid, saturated solution)

Joining process: centrifuge dropping of the bridging solution with a pipette, adjustment time 3 min, then 25 min with 400g weighted at room temperature and normal atmosphere, drying in air 20 min at room temperature, drying oven 8 h at 80 ⁰ C, normal atmosphere. Result: Extension of the adjustment time by addition of B2O3 and reduction of the pH to 11, 9 to 3 min, boric acid H3BO3 is in water at

Warming light, sparingly soluble in the cold, it is a weak acid and serves to neutralize the basic waterglass solution, delays their chemical reactions with the joining surfaces and the CO _{2 of} the air and the formation of water-insoluble boro-silicate bonds Si-OB made of water-soluble alkali borates, thus extending the joining and adjustment times, fixed joint, joint surface optically clear and transparent.

Optical assessment: grade 1

Embodiment 3

Low-temperature bonding of two ULE blanks

Cleaning: RCA cleaning Fusing solution: Silica sol Levasil 300/30% + 1% by volume tetraethyl orthotitanate (3%

Mass content) + 2% by volume NH ₃ - Na ₂ CO ₃ (10% ml NH _{3 aq} 24% in water + 10 g

Na ₂ CO ₃ ).

Joining process: centrifuge dropping of the bridging solution with a pipette, adjustment time 4 min, weight (100 g) for 5 min, drying in air for 20 min at room temperature and normal atmosphere, then 8 h heat treatment in a drying oven at 80 ⁰ C and normal atmosphere. Result: Adjustment time up to 4 min using a base solution of silica sol (pH 10.1) and addition of a titanium-containing compound as well as stabilization of the bridging solution with (NH ₄ ) ₂ CO ₃ . The pH of the resulting bridging solution is 9.8. In addition, since ULE is composed of SiO ₂ and TiO ₂ , the titanium-containing compound results in higher joining strength (40 MPa instead of 30 MPa compared to a silica sol solution without Ti compound). This gives a stable joint with optically clear and transparent joining surface.

Optical assessment: grade 1

Embodiment 4

Low-temperature fusion of two Zerodur blanks

Cleaning: RCA cleaning

Fung solution: lithium-waterglass solution + aluminum silicate solution (volume ratio 9: 1) + 5% by volume of ammoniacal solution (NH ₃ H ₂ O, 24% in water, company Fluka), pH of the bridging solution 11, 6. Joining process: central dripping of the joint solution with a glass rod, adjustment time 4 min, weight (400 g) for 60 min, drying in air at room temperature and normal atmosphere for 20 min, then 8 h heat treatment in a drying oven at 80 ^° C. and normal atmosphere. Result: Adjustment time up to 4 min by addition of aluminum silicate solution and ammoniacal solution (NH ₃ H ₂ O) to the lithium water glass, ammoniacal solution (NH ₃ H ₂ O) dissolves in the basic lithium silicate solution in the meantime formed aluminum hydroxide to complex, this Solution acts as a buffer solution. This gives a stable joint, but no optically clear and transparent, but a uniformly milky joint surface. The method is therefore suitable for joints in which no optical passage through the joining surfaces is needed.

Visual assessment: grade 4 Embodiment 5

Low-temperature fusion of two Zerodur blanks

Cleaning: RCA cleaning Masterbatch solution: 90% by mass Lithium-water glass solution (ISC 1) + 10% by mass Zinc acetate (pH of the bonding solution 11, 4)

Joining process: centrifuge dropping of the bridging solution with a pipette, adjustment time 5 min, weight (100 g) for 5 min, drying in air for 20 min at room temperature and normal atmosphere, then 8 h heat treatment in a drying oven at 80 ⁰ C and normal atmosphere. Result: Adjustment time up to 5 min by addition of zinc acetate to sodium waterglass solution, zinc acetate reacts with the strongly basic sodium silicate solution to zinc hydroxide. Zn (OH) ₂ is amphoteric and tends to complex formation in excess liquor, goes into solution and leads to a moderate reduction in the pH of the joint solution. This gives a stable joint, but no optically clear and transparent, but a partially milky joint surface. The method is suitable for joints in which no optical passage through the joining surfaces is needed.

Visual assessment: grade 4

Embodiment 6

Low-temperature insertion of a ULE blank and a BK7 blank

Cleaning: Bath cleaning Fung solution: 95% by volume ISC 3 (Na water glass: water = 1: 2), 5% by volume trimethyl borate (purum> 99.0%, Fluka)

Joining process: Joining by pushing in the parts to be joined, adjustment time 4 min, weight bearing (500 g) for 15 min in air at room temperature, then 72 h curing under vacuum (5 mbar) at room temperature, followed by heat treatment in a vacuum oven (5 mbar, 70 ^° C.). Heating rate 20 K / h, 24 h). Result: The adjustment time was increased by dilution to 4 min, giving a firm joining with an optically clear and transparent joining surface, only occasional bubbles.

Visual assessment: grade 2

Three-point bending strength: 53 MPa Layer thickness: 0.7 μm Embodiment 7

Low temperature insertion of a ULE blank and a Lithosil blank

Cleaning: RCA cleaning

Bonding solution: 90% by volume of ISC 3 (Na water glass: water = 1: 2), 8% by volume of TiO ₂ in water

(1% by mass), stabilized by 2% by volume of (NH ₄ ) ₂ CO ₃ (100 ml NH _{3 aq} 24% in

Water + 1 O g Na ₂ CO ₃ ), pH of the fusing solution 11, 5

Joining process: Joining by pushing in the parts to be joined, adjustment time 4 min, weight bearing (400 g) for 15 min in air at room temperature, then 72 h

Curing in air at room temperature, followed by heat treatment in

Drying cabinet (80 ⁰ C, 24 h).

Result: Adjustment time increased to 4 min, fixed joint, optically clear and transparent

Joining surface.

Visual evaluation: Grade 1 Three-point bending strength: 50 MPa Layer thickness: 0.7 μm

Claims

claims

1. A method for joining two or more components made of glass, ceramic and / or glass ceramic with the aid of a waterglass fusing solution with sodium, potassium and / or lithium ions and / or a silica sol, in which the fusing solution or the silica sol on joining surfaces is brought between the components to be joined and solidified at mild temperatures, characterized in that the fusing solution contains at least one additive selected from boric acid, boron compounds from which boric acid can be formed by hydrolysis, aluminum acetates, aluminum silicates, titanium compounds which are soluble in aqueous solution of titanium. Forming hydroxocations, water-soluble zinc compounds, water-soluble zirconium compounds and water-soluble yttrium compounds, which additive is added in an amount which reduces the pH of the underlying water glass fuser solution or the underlying silica sol.

2. A method for joining two or more components made of glass, ceramic and / or glass ceramic with the aid of a water glass-fusing solution with sodium, potassium and / or lithium ions and / or a silica sol, in which the fusing solution or the silica sol on joining surfaces placed between the components to be joined and solidified at mild temperatures, preferably according to claim 1, wherein after applying the Fügelösung and joining the components to be joined and their fixation drying of the joined components by removing water at room temperature, characterized in that the drying of a heat treatment of the joined components in a vacuum at a temperature ranging from above room temperature up to 200 ⁰ C.

3. The method of claim 1 or 2, wherein the components are cleaned prior to joining with an RCA cleaning process or a bath cleaning.

4. The method according to any one of claims 1 to 3, wherein the joining surfaces of the components before the joining with a basic medium, preferably NaOH and / or KOH, or an acidic medium, preferably HF, are pretreated.

5. The method according to any one of the preceding claims, wherein the joining surfaces of the components are silanized before joining, preferably using fluorosilanes, in particular perfluorododecyl-triethoxysilane, organically crosslinkable alkoxysilanes, in particular 3-methacryloxy-propyltrimethoxysilane and / or amino-modified alkoxysilanes, in particular Amino- propyltrimethoxysilane, such that a hydrophobic contact angle in the range of 50 ° to 75 ° is formed.

6. The method according to any one of the preceding claims, wherein the components to be joined are provided before the low-temperature joining via a PVD process, in particular by sputtering, with a thin SiO ₂ layer.

7. The method according to any one of the preceding claims, wherein the foaming solution is based on a water glass solution of Na2Si3θ ₇ , K ₂ SJsO ₇ , Li ₂ SIsO ₇ and / or a silica sol with 100 m ² / g SiO ₂ /45% SiO ₂ / 100 parts of silica sol, 200 m ² / g SiO ₂ MO% _SiO2 / 100 parts silica sol or 300 m ² / g SiO _2/30% _SiO2 / 100 parts silica sol contains water in a concentration of 10 to 99 vol .-% , and in particular neutral to slightly basic sodium silicate with a molar ratio SiO ₂ : Na ₂ O of 3.5 (solids content about 39%), potassium water glass with a molar ratio SiO ₂ : K ₂ O of 2.9 (solids content about 40%) or lithium water glass with a molar ratio SiO ₂ : Li ₂ O 2.5 (solids content about 27.2%).

A process according to any one of the preceding claims wherein the bridging solution contains up to 50% by volume of an ammoniacal solution in water, preferably 24% NH ₃ in water.

A process according to any one of the preceding claims wherein the bridging solution contains up to 50% by mass of one or more of the following compounds: B ₂ O ₃ in the form of a saturated suspension in water in a proportion of up to 5% by volume),

Boric acid H3BO3,

Trimethyl borate B (OCH ₃ ) ₃ ,

aluminum silicate,

AI (OOCCHS) ₃ ,

HOAI (OOCCHS) ₂ ,

Tetraisopropyl orthotitanate (titanium IV isopropylate), titanium (IV) ethylate,

titanium acetylacetonate,

Titanium Hydrate TiSO ₄ x H ₂ O,

TiO ₂ in H ₂ O in an amount of up to 1% by mass,

zinc acetate,

Zinc sulfate-7-hydrate,

Zinc nitrate,

Zirconium sulfate Zr (SO ₄ ) ₂ ,

Zirconium (IV) isopropoxide-isopropanol complex,

Zirconium propylate 77% in n-propanol,

Zirconium 2,4 pentanedionate,

Zirconium nitrate (Zr (NOs) ₄ ),

Zirconium n-propylate,

Zirconium (IV) oxide in water in an amount of up to 1% by mass),

Zirconium ethoxide,

Zirconium (IV) oxychloride 8-hydrate,

Yttrium nitrate Y (NOs) ₃ × 6 H ₂ O,

Yttrium chloride hexahydrate,

Yttrium acetate hydrate in an amount of up to 1% by volume.

A process according to any one of the preceding claims, wherein the pH of the bridging solution is between 9 and 13 and preferably between 10 and 12.6.

11. The method according to any one of the preceding claims, wherein the joining temperature below 100 ⁰ C, and preferably between 50 and 80 ⁰ C.

12. The method according to any one of the preceding claims, wherein after the application of the Fügelösung a period of 3 to 6 minutes remains to adjust the components to each other.

13. The method according to any one of the preceding claims, wherein after applying the Fügelösung and an adjustment of the components to each other, a drying of the joined components at room temperature in air in a dehydrating environment, such as a desiccator, or in the dry N ₂ gas stream.

14. The method according to claim 13, wherein the duration of the drying is 2 minutes to 8 days, preferably 5 to 60 minutes and particularly preferably 5 to 15 minutes.

15. The method according to any one of claims 13 or 14, wherein the drying is carried out at room temperature in vacuo with a pressure of <10 mbar and preferably at 0.1 mbar to 2 mbar.

16. The method of claim 15, wherein the drying in vacuum is supported by infrared radiation and the temperature in the joining zone does not rise above 50 degrees Celsius and preferably does not rise above 30 Celsius.

17. The method according to any one of claims 13 to 16, wherein the drying is carried out in vacuo, preferably at a pressure of <10 mbar, more preferably at about 0.5 to 2 mbar and particularly preferably at about 1 mbar.

18. The method according to any one of claims 13 to 17, characterized in that after drying a tempering of the joined components takes place in a vacuum.

19. The method according to claim 18, characterized in that the heat treatment at a pressure of less than 10 mbar and preferably at 0.1 mbar to 2 mbar and / or at a temperature in the range between 50 ⁰ C and 150 ⁰ C, preferably between 70 ° C and 120 ⁰ C.

20. The method according to any one of claims 18 or 19, wherein the annealing for a period of 2 minutes to two weeks, preferably from 1/2 day to 1 week, more preferably from 8h to 72 h, and most preferably from

8 to 24 h is performed.

21. The method according to any one of claims 13 to 20, wherein the drying and / or tempering is carried out under the application of a weight by which a pressure of 1000 to 100000 N / m ² , preferably from about 10000 N / m ² on the bonding surface of Parts acts.

22. The method according to any one of the preceding claims, wherein the components to be joined made of glass, in particular of soda lime silicate, Borkronglas, Borofloatglas, silica glass or doped silica glass, or of glass ceramic, in particular Zerodur exist.

23. The method according to any one of the preceding claims, wherein the gap between the components to be joined has a thickness of <2 microns, preferably <160 nm and wherein the surfaces of the components to be joined at the joining surfaces a flatness deviation (PV = peak-to-valley ) of less than 160 nm and a roughness (RMS = root-mean-square) of less than 30 nm, preferably less than 3 nm, and most preferably less than 1 nm.

24. The method according to any one of the preceding claims, wherein the components to be joined are optical components, micromechanical components or materials which preferably do not expand when temperature changes.